Structure, function, and chemical synthesis of Vaejovis mexicanus peptide 24: a novel potent blocker of Kv1.3 potassium channels of human T lymphocytes.

Animal venoms are rich sources of ligands for studying ion channels and other pharmacological targets. Proteomic analyses of the soluble venom from the Mexican scorpion Vaejovis mexicanus smithi showed that it contains more than 200 different components. Among them, a 36-residue peptide with a molecular mass of 3864 Da (named Vm24) was shown to be a potent blocker of Kv1.3 of human lymphocytes (K(d) ∼ 3 pM). The three-dimensional solution structure of Vm24 was determined by nuclear magnetic resonance, showing the peptide folds into a distorted cystine-stabilized α/ß motif consisting of a single-turn α-helix and a three-stranded antiparallel ß-sheet, stabilized by four disulfide bridges. The disulfide pairs are formed between Cys6 and Cys26, Cys12 and Cys31, Cys16 and Cys33, and Cys21 and Cys36. Sequence analyses identified Vm24 as the first example of a new subfamily of α-type K(+) channel blockers (systematic number α-KTx 23.1). Comparison with other Kv1.3 blockers isolated from scorpions suggests a number of structural features that could explain the remarkable affinity and specificity of Vm24 toward Kv1.3 channels of lymphocytes.

Estudios bioecológicos de Aedes (St.) aegypti en un área urbana de Camagüey con baja densidad del vector / Bioecological studies of Aedes (St.) aegypti in an urban area with low vector density in Camagüey province

INTRODUCCION: el control de los sitios de cría de mosquitos de relevancia médica es esencial en los programas de lucha antivectorial, sin embargo, los esfuerzos ejecutados hasta la actualidad no han sido suficientes por el aumento paulatino de casos confirmados de fiebre de dengue. OBJETIVO: informar sobre los principales sitios de cría de Aedes aegypti, en un ambiente urbano de Camagüey con baja densidad del vector. MÉTODOS: el universo urbano se inspeccionó en su totalidad entre enero y diciembre de 2007. En los depósitos positivos la colecta fue según metodología del Programa Nacional de Control de Vectores. Cada depósito fue caracterizado mediante una planilla de investigación de manzana positiva implementada al efecto. Se determinó el porcentaje de representatividad de cada depósito positivo, así como la proporción de larvas por cada depósito. RESULTADOS: Aedes aegypti colonizó 44 depósitos diferentes con destaque para artificiales (97,73 por ciento). La mayoría fueron permanentes, útiles y no modificables. Siguiendo el criterio de la población la combinación permanentes + útiles se cumple en 17 tipos de depósitos que representan 38,63 por ciento, y aportan un total de 180 recipientes positivos para 81,08 por ciento. Los tanques bajos contribuyeron a 36,03 por ciento de la positividad. CONCLUSIONES: la elevada positividad en depósitos que pudieron ser evitados por la población obliga a elevar la responsabilidad individual en el mejoramiento del saneamiento doméstico y, con ello, la concientización cívica para alcanzar una activa participación comunitaria en este sentido. Esto junto al fortalecimiento de la transectorialidad, permitirá impactar en la eliminación y disposición final de todo material inservible y que pueda servir de criadero a los mosquitos.

INTRODUCTION: the control of the breeding sites of mosquitoes of medical importance is essential for the anti-vector fighting programs; however, the efforts made so far have not great enough since the confirmed dengue fever cases gradually increase. OBJECTIVE: to provide information on the main breeding sites of Aedes aegypti in an urban area with low vector density in Camagüey province. METHODS: the urban universe was fully surveyed from January to December 2007. The collection procedure in the positive containers followed the National Vector Control program methodology. The characteristics of each container were written in a customized study form of positive blocks. The representative percentage of each positive container, as well as the proportion of larvae per container were determined. RESULTS: Aedes aegypti formed colonies in 44 different containers, being the artificial reservoirs the predominant ones (97.73 percent). The majority were permanent, useful and unchangeable. Following the population's criteria, the combination of permanent plus useful is valid in 17 types of containers accounting for 38.36 percent and contributing 180 positive containers for 81.08 percent of the total number. The tanks placed on the ground reached 36.03 percent positivity. CONCLUSIONS: the high number of mosquito-positive tanks demands greater individual responsibility in improving domestic sanitation and thus, the increase of awareness in order to achieve more active community involvement in this regard. The latter together with the strengthening of transectoriality will allow having an impact on the elimination and final disposal of all the useless materials that may serve as possible breeding sites of mosquitoes.

[Bioecological studies of Aedes (St) aegypti in an urban area with low vector density in Camagüey province]. / Estudios bioecológicos de Aedes (St.) aegypti en un area urbana de Camagüey con baja densidad del vector.

INTRODUCTION: The control of the breeding sites of mosquitoes of medical importance is essential for the anti-vector fighting programs; however, the efforts made so far have not great enough since the confirmed dengue fever cases gradually increase. OBJECTIVE: To provide information on the main breeding sites of Aedes aegypti in an urban area with low vector density in Camagüey province. METHODS: The urban universe was fully surveyed from January to December 2007. The collection procedure in the positive containers followed the National Vector Control program methodology. The characteristics of each container were written in a customized study form of positive blocks. The representative percentage of each positive container, as well as the proportion of larvae per container were determined. RESULTS: Aedes aegypti formed colonies in 44 different containers, being the artificial reservoirs the predominant ones (97.73%). The majority were permanent, useful and unchangeable. Following the population's criteria, the combination of permanent plus useful is valid in 17 types of containers accounting for 38.36% and contributing 180 positive containers for 81.08% of the total number. The tanks placed on the ground reached 36.03% positivity. CONCLUSIONS: The high number of mosquito-positive tanks demands greater individual responsibility in improving domestic sanitation and thus, the increase of awareness in order to achieve more active community involvement in this regard. The latter together with the strengthening of transectoriality will allow having an impact on the elimination and final disposal of all the useless materials that may serve as possible breeding sites of mosquitoes.

Aedes (St.) aegypti en tanques bajos y sus implicaciones para el control del dengue en Camagüey / Presence of Aedes (St.) aegypti in water tanks on the ground and the implications for dengue control in Camagüey province

INTRODUCCION: los tanques bajos son un importante reservorio doméstico de agua potable, que Aedes aegypti está colonizando con notable frecuencia en el ambiente urbano en un área de salud de la provincia de Camagüey, Cuba. OBJETIVO: determinar el aporte entomológico que brindan los tanques bajos, un depósito artificial de amplia distribución al nivel comunitario, a la infestación por Aedes aegypti que se reporta en un área de salud urbana de la provincia de Camagüey. MÉTODOS: del total general de depósitos positivos se cuantificaron los tanques bajos, para determinar el índice recipiente específico (IRe) junto al promedio de pupas/tanque bajo positivo; estos tanques fueron caracterizados durante la investigación de la vivienda mediante una planilla implementada al efecto. Se determinó igualmente el total de horas promedio que durante el día permanecen destapados. RESULTADOS: los tanques bajos aportaron 36,03 por ciento de positividad en relación con el total general, recibían mayormente agua del acueducto público en el exterior de las viviendas, con un IRe= 2,69. Más de 97 por ciento está sin la debida hermeticidad de su tapa; 92,5 por ciento se mantenían destapados cerca de 6 a 7 h durante el día. En 17 tanques positivos se colectaron 41 pupas para promediar 2,41 pupas/tanques bajos. CONCLUSIONES: el aporte de los tanques bajos a la positividad del área, obliga a priorizar su inspección y cuidado por parte de la población y el personal especializado, puesto que la distribución de tapas no será una solución definitiva si no se modifica la conducta del morador. Ello requiere mejorar la información que se le brinda a la población, para contribuir a modificar la percepción de riesgo y elevar el nivel de conocimientos sobre el tema. De esta forma se logrará contribuir a propiciar una incorporación más activa y consciente de la comunidad al proceso, como elemento fundamental para hacerlo realmente sostenible.

INTRODUCTION: water tanks placed on the ground are an important drinking water container at home; however, Aedes aegypti is very frequently colonizing this kind of reservoirs in an urban health area of Camaguey province, Cuba. OBJECTIVES: to determine the entomological contribution of these water tanks widely distributed containers at community setting- to infestation by Aedes aegypti in an urban health area of Camaguey province. METHODS: out of the total number of containers positive to Aedes aegypty, the amount of water tanks involved was estimated, in order to determine the specific container rate (sCR) together with the average of pupas per positive water tank on the ground. These tanks were characterized during the study of the house using an application form prepared to this end. Similarly, the average total number of hours that the tanks remained uncovered was estimated. RESULTS: it was found that 36.03 percent of all positive containers were water tanks on the ground, which were mostly filled with water from the aqueduct outdoors; being the sCR=2.69. Over 97 percent of them had faulty covers whereas 92.5 percent remained uncovered for 6 or 7 hours a day. Seventeen positive tanks sheltered 41 pupas for an average of 2,41 pupas per tank. CONCLUSIONS: the contribution of water tanks on the ground to the presence of Aedes aegypti pupas in the area makes it necessary to give priority to the inspection and surveillance of such containers on the part of the population and the expert staff. The supply of new covers will not represent the final solution to this problem if the behaviour of the dwellers in a house does not change. It is required to improve the information to be provided to the population so that the risk perception is changed and the level of knowledge on this topic is raised. In this way, it will be possible to involve the community more actively in this process as a key element to make it really sustainable.

[Presence of Aedes aegypti in water tanks on the ground and the implications for dengue control in Camagüey province]. / Aedes (St.) aegypti en tanques bajos y sus implicaciones para el control del dengue en Camagüey.

INTRODUCTION: Water tanks placed on the ground are an important drinking water container at home; however, Aedes aegypti is very frequently colonizing this kind of reservoirs in an urban health area of Camagüey province, Cuba. OBJECTIVES: to determine the entomological contribution of these water tanks -widely distributed containers at community setting- to infestation by Aedes aegypti in an urban health area of Camagüey province. METHODS: Out of the total number of containers positive to Aedes aegypty, the amount of water tanks involved was estimated, in order to determine the specific container rate (sCR) together with the average of pupas per positive water tank on the ground. These tanks were characterized during the study of the house using an application form prepared to this end. Similarly, the average total number of hours that the tanks remained uncovered was estimated. RESULTS: It was found that 36.03 % of all positive containers were water tanks on the ground, which were mostly filled with water from the aqueduct outdoors; being the sCR = 2,69. Over 97% of them had faulty covers whereas 92.5% remained uncovered for 6 or 7 hours a day. Seventeen positive tanks sheltered 41 pupas for an average of 2.41 pupas per tank. CONCLUSIONS: The contribution of water tanks on the ground to the presence of Aedes aegypti pupas in the area makes it necessary to give priority to the inspection and surveillance of such containers on the part of the population and the expert staff The supply of new covers will not represent the final solution to this problem if the behaviour of the dwellers in a house does not change. It is required to improve the information to be provided to the population so that the risk perception is changed and the level of knowledge on this topic is raised. In this way, it will be possible to involve the community more actively in this process as a key element to make it really sustainable.

Infestación de Aedes (St) aegypti en bebederos de animales en un área de salud / Aedes (St) aegypti infestation of troughs for animals in a health area

Aedes aegypti, importante vector del dengue/dengue hemorrágico, tiene al ambiente urbano como sitio preferencial para su desarrollo, el cual es muy inestable y le brinda numerosos recursos para su superviviencia. Evaluar el aporte entomoepidemiológico que brindan los bebederos de animales, en la infestación de Ae. aegypti en un área de salud urbana de la provincia de Camagüey. Se determinó el total de bebederos positivos desglosado según el tipo de animal que lo utiliza, así como el porcentaje de bebederos positivos indicado como índice recipiente específico (IRe). Se determinó además el total de bebederos con presencia de pupas, así como el total de estas por tipo de depósito, cada uno fue caracterizado. Se apreció que los bebederos aportaron 4,62 por ciento de positividad, con un índice recipiente específico equivalente a 0,74 por ciento, de ellos 6 eran utilizados por gallinas, 5 por conejos y 1 por monos y perros, respectivamente. Fueron detectadas 6 pupas (0,46 pupa/bebedero). Estos receptáculos que se caracterizaron por encontrarse ubicados en el exterior de las viviendas, y la mayoría a la sombra, a pesar de no aportar un número importante de focos deben tenerse en cuenta para el diseño de las estrategias de control, lo que contribuirá a garantizar la no existencia de huevos residuales del vector en las viviendas.

Aedes aegypti, important vector of dengue/hemorrhagic dengue, prefer the urban environment for its very unstable development since it provides it with a number of possibilities for its survival. To evaluate the entomological and epidemiological contributions of troughs for animals to Ae aegyti infestation in an urban health area in Camagüey province, Cuba. The total number of troughs positive to the mosquito, broken down by type of animal using it, as well as the percentage of positive troughs taken as specific reservoir index were estimated. Also, all the troughs containing pupas and the total number of pupas per type of trough were determined; each of them was characterized. It was observed that troughs represented 4.62 percent of positive sites, with a specific reservoir index equals to 0.74 percent; 6 troughs were used by chicken, 5 by rabbits and one by monkeys and the other by dogs. Six pupas were detected (0.46 pupa/trough). These reservoirs that are mainly placed outdoors in shady areas, though they did not give rise to a substantial number of foci, one must be taken it into account to designing new control strategies, which will help in assuring the non-existence of residual eggs in dwellings.

A selective blocker of Kv1.2 and Kv1.3 potassium channels from the venom of the scorpion Centruroides suffusus suffusus.

A novel potassium channel blocker peptide was purified from the venom of the scorpion Centruroides suffusus suffusus by high-performance liquid chromatography and its amino acid sequence was completed by Edman degradation and mass spectrometry analysis. It contains 38 amino acid residues with a molecular weight of 4000.3Da, tightly folded by three disulfide bridges. This peptide, named Css20, was shown to block preferentially the currents of the voltage-dependent K+-channels Kv1.2 and Kv1.3. It did not affect several other ion channels tested at 10 nM concentration. Concentration-response curves of Css20 yielded an IC50 of 1.3 and 7.2 nM for Kv1.2- and Kv1.3-channels, respectively. Interestingly, despite the similar affinities for the two channels the association and dissociation rates of the toxin were much slower for Kv1.2, implying that different interactions may be involved in binding to the two channel types; an implication further supported by in silico docking analyses. Based on the primary structure of Css20, the systematic nomenclature proposed for this toxin is alpha-KTx 2.13.

Proteomic analysis of the venom from the fish eating coral snake Micrurus surinamensis: novel toxins, their function and phylogeny.

The protein composition of the soluble venom from the South American fish-eating coral snake Micrurus surinamensis surinamensis, here abbreviated M. surinamensis, was separated by RP-HPLC and 2-DE, and their components were analyzed by automatic Edman degradation, MALDI-TOF and ESI-MS/MS. Approximately 100 different molecules were identified. Sixty-two components possess molecular masses between 6 and 8 kDa, are basically charged molecules, among which are cytotoxins and neurotoxins lethal to fish (Brachidanios rerio). Six new toxins (abbreviated Ms1-Ms5 and Ms11) were fully sequenced. Amino acid sequences similar to the enzymes phospholipase A2 and amino acid oxidase were identified. Over 20 additional peptides were identified by sequencing minor components of the HPLC separation and from 2-DE gels. A functional assessment of the physiological activity of the six toxins was also performed by patch clamp using muscular nicotinic acetylcholine receptor assays. Variable degrees of blockade were observed, most of them reversible. The structural and functional data obtained were used for phylogenetic analysis, providing information on some evolutionary aspects of the venom components of this snake. This contribution increases by a factor of two the total number of alpha-neurotoxins sequenced from the Micrurus genus in currently available literature.

Transcriptome analysis of the venom gland of the Mexican scorpion Hadrurus gertschi (Arachnida: Scorpiones).

BACKGROUND: Scorpions like other venomous animals possess a highly specialized organ that produces, secretes and disposes the venom components. In these animals, the last postabdominal segment, named telson, contains a pair of venomous glands connected to the stinger. The isolation of numerous scorpion toxins, along with cDNA-based gene cloning and, more recently, proteomic analyses have provided us with a large collection of venom components sequences. However, all of them are secreted, or at least are predicted to be secretable gene products. Therefore very little is known about the cellular processes that normally take place inside the glands for production of the venom mixture. To gain insights into the scorpion venom gland biology, we have decided to perform a transcriptomic analysis by constructing a cDNA library and conducting a random sequencing screening of the transcripts. RESULTS: From the cDNA library prepared from a single venom gland of the scorpion Hadrurus gertschi, 160 expressed sequence tags (ESTs) were analyzed. These transcripts were further clustered into 68 unique sequences (20 contigs and 48 singlets), with an average length of 919 bp. Half of the ESTs can be confidentially assigned as homologues of annotated gene products. Annotation of these ESTs, with the aid of Gene Ontology terms and homology to eukaryotic orthologous groups, reveals some cellular processes important for venom gland function; including high protein synthesis, tuned posttranslational processing and trafficking. Nonetheless, the main group of the identified gene products includes ESTs similar to known scorpion toxins or other previously characterized scorpion venom components, which account for nearly 60% of the identified proteins. CONCLUSION: To the best of our knowledge this report contains the first transcriptome analysis of genes transcribed by the venomous gland of a scorpion. The data were obtained for the species Hadrurus gertschi, belonging to the family Caraboctonidae. One hundred and sixty ESTs were analyzed, showing enrichment in genes that encode for products similar to known venom components, but also provides the first sketch of cellular components, molecular functions, biological processes and some unique sequences of the scorpion venom gland.

Presencia y disrribución de corbicula fluminea müller, 1774) (bivalvia: corbicculidae) en camagüey, un probable competidor de moluscos de interés saiitario / Presence and distribution of Corbicula Fluminea (Müller, 1774) (Bivalvia: Corbiculidae) in Camagüey, a probable molluscs competitor of sanitary interest

Se realizaron 189 prospecciones malacológicas en igual número de cuerpos de agua de la provincia Camagüey, con el objetivo de conocer la actual actividad dispersiva de Corbicula fluminea,un bivalvo con probable utilización como biorregulador de otras especies de moluscos indeseables. Se reportó su presencia en lagunas, ríos y micropresas de los municipios de Céspedes, Florida, Vertientes y Jimaguayú (30.8 % del total de municipios), así como en el 6.3 % del total de cuerpos de agua muestreados. Jimaguayú aportó el 50 % del total espejos habitas con presencia de esta almeja dulceacuícola. La temperatura (R=0.6286, R2=0.395, b=0.629, p<0.0414), fue la única variable abiótica con importante influencia sobre la densidad del molusco. El modelo teórico para calcular la densidad resultó ser D= ­216.23+0.629 (temperatura).

One-hundred eighty-nine malacologic researches were carried out in equal number of water bodies of Camagüey province, with the objective to know the current dispersal activity of Corbicula Fluminea, a bivalve with probable utilization as bioregulating, of other undesirable molluscs species. Its presence in lagoons, rivers, and small dams of Céspedes, Florida, Vertientes and Jimaguayú municipalities was reported, (30.8% of the total of municipalities), as well as in the 6.3% of the total sampled water bodies. Jimaguayú contributed the 50% of the total habitat mirrors with presence of this clam. The temperature (R=0.6286; R2=0.395, b=0.629; p<0.0414), was the only abiotic variable with important influence on the density of the mollusc. The theoretical model to calculate the abundance turned out to be density = ¬216.23 + 0.629 (temperature).

Wide phylogenetic distribution of Scorpine and long-chain beta-KTx-like peptides in scorpion venoms: identification of "orphan" components.

Scorpine and toxins specific for potassium channels of the family beta (beta-Ktx) are two types of structurally related scorpion venom components, characterized by an unusually long extended N-terminal segment, followed by a Cys-rich domain with some resemblance to other scorpion toxins. In this communication, we report evidence supporting the ubiquitous presence of Scorpine and beta-KTx-like polypeptides and their precursors in scorpions of the genus Tityus of the family Buthidae, but also included is the first example of such peptides in scorpions from the family Iuridae. Seven new beta-KTxs or Scorpine-like peptides and precursors are reported: five from the genus Tityus (T. costatus, T. discrepans and T. trivittatus) and two from Hadrurus gertschi. The cDNA precursors for all of these peptides were obtained by molecular cloning and their presence in the venoms were confirmed for various peptides. Analysis of the sequences revealed the existence of at least three distinct groups: (1) beta-KTx-like peptides from buthids; (2) Scorpine-like peptides from scorpionid and iurid scorpions; (3) heterogeneous peptides similar to BmTXKbeta of buthids and iurids. The biological function for most of these peptides is not well known; that is why they are here considered "orphan" peptides.

Overview of scorpion toxins specific for Na+ channels and related peptides: biodiversity, structure-function relationships and evolution.

Scorpion venoms contain a large number of bioactive components. Several of the long-chain peptides were shown to be responsible for neurotoxic effects, due to their ability to recognize Na(+) channels and to cause impairment of channel functions. Here, we revisited the basic paradigms in the study of these peptides in the light of recent data concerning their structure-function relationships, their functional divergence and extant biodiversity. The reviewed topics include: the criteria for classification of long-chain peptides according to their function, and a revision of the state-of-the-art knowledge concerning the surface areas of contact of these peptides with known Na(+) channels. Additionally, we compiled a comprehensive list encompassing 191 different amino acid sequences from long-chain peptides purified from scorpion venoms. With this dataset, a phylogenetic tree was constructed and discussed taking into consideration their documented functional divergence. A critical view on problems associated with the study of these scorpion peptides is presented, drawing special attention to the points that need revision and to the subjects under intensive research at this moment, regarding scorpion toxins specific for Na(+) channels and the other related long-chain peptides recently described.

NMR solution structure of Cn12, a novel peptide from the Mexican scorpion Centruroides noxius with a typical beta-toxin sequence but with alpha-like physiological activity.

Cn12 isolated from the venom of the scorpion Centruroides noxius has 67 amino-acid residues, closely packed with four disulfide bridges. Its primary structure and disulfide bridges were determined. Cn12 is not lethal to mammals and arthropods in vivo at doses up to 100 microg per animal. Its 3D structure was determined by proton NMR using 850 distance constraints, 36 phi angles derived from 36 coupling constants obtained by two different methods, and 22 hydrogen bonds. The overall structure has a two and half turn alpha-helix (residues 24-32), three strands of antiparallel beta-sheet (residues 2-4, 37-40 and 45-48), and a type II turn (residues 41-44). The amino-acid sequence of Cn12 resembles the beta scorpion toxin class, although patch-clamp experiments showed the induction of supplementary slow inactivation of Na(+) channels in F-11 cells (mouse neuroblastoma N18TG-2 x rat DRG2), which means that it behaves more like an alpha scorpion toxin. This behaviour prompted us to analyse Na(+) channel binding sites using information from 112 Na(+) channel gene clones available in the literature, focusing on the extracytoplasmic loops of the S5-S6 transmembrane segments of domain I and the S3-S4 segments of domain IV, sites considered to be responsible for binding alpha scorpion toxins.

Current views on scorpion toxins specific for K+-channels.

Much of our knowledge on K+-channels was elucidated using specific peptide ligands isolated from a number of venomous organisms. Recently, this field received a strong support and increased interest due to the solution of the three-dimensional structure of a couple of K+-channels. At the same time, several new subfamilies of specific toxins for K+-channels were isolated from scorpion venoms, enhancing the availability and diversity of such useful molecular tools. It opened new lines of research for the better understanding of K+-channel biophysics and pharmacology. In this review, we listed 120 amino acid sequences of peptides isolated from scorpion venoms. They were demonstrated or assumed to be specific for K+-channels. These sequences were aligned and used to generate a rooted phylogenetic tree. The evolutionary tree indicates that several clusters of divergent peptides show preference for specific subtypes of channels. The three-dimensional structures of representative examples of these peptides were drawn and analysed concerning the molecular fitness of their interactions with the channel targets. Four different interacting modes were identified to exist between scorpion toxins and the various subtypes of K+-channels.

[Change of the weight/ foot area coefficient in relation to aggregation in Tarebia granifera]. / Modificación del coeficiente peso/área del pié en relación con la agregación en Tarebia granifera.

OBJECTIVE: To analyze specimens dispersion in a population of Tarebia granifera and its relationship with the change of morphometric parameters. METHODS: Two samplings by parcels including two types of substrata in opposite aggregation conditions were carried out, and the specimen abundance was compared between both samplings and substrata. The samples were stratified into classes according to shell height and for each of these the coefficient weight/foot-area was calculated and correlated with class size. It was experimentally evaluated whether specimens with a lower foot load had a better persistence in emerged substratum as well as the interaction between two class groups of shell height. RESULTS: The abundance difference between samplings was t=5.874 (p<0.001), and t=10.15 (p<0.001) between emerged rocky and sandy substrata, only under conditions of high aggregation where foot load decreases with the size for higher specimens (r=-0.98, p<0.05). Experimentally, the abundance of specimens of opposed sizes were mutually limited (r=-0.87, p<0.01), waves' height limits the abundance of smaller snails (r=-0.94, p<0.01) but it is tolerated by larger ones (r=0.72, p<0.05), and foot load diminishes with the waves' height (r=-0.93, p<0.001). CONCLUSIONS: Under high aggregation conditions larger specimens emigrate toward substratum of difficult capture by smaller ones, which are limited by the environment's mechanical influence. The decrease of foot load facilitates specimens' dispersion.

Modificación del coeficiente peso/área del pié en relación con la agregación en Tarebia granifera / Change of the weight/foot area coefficient in relation to aggregation in Tarebia granifera

OBJETIVO: Analizar la dispersión de los ejemplares de una población de Tarebia granifera y su relación con la modificación de los parámetros morfométricos. METODOS: Se colectó por parcelas incluyendo dos tipos de substratos en condiciones opuestas de agregación y se comparó la abundancia relativa tanto entre muestreos, como entre sustratos. Se delimitaron 7 clases de alto a las cuales se les determinó el coeficiente peso/área del pié, el cual se correlacionó con la talla por clase. Se evaluó experimentalmente si los individuos con menor carga del pié tienen mayor persistencia en substratos emergidos, así como la interacción entre dos grupos de clases de alto. RESULTADOS: La diferencia de la abundancia entre los muestreos fue de t=5.874 (p<0.001) y de t=10.15 (p<0.001) entre el substrato rocoso emergido y el arenoso, sólo en condiciones de alta agregación, en las que la carga del pié de los individuos más grandes se reduce con la talla (r=-0.98, p<0.05). Experimentalmente, la abundancia de los ejemplares de tallas opuestas está mutuamente limitada (r=-0.87, p<0.01), la altura del oleaje limita la abundancia de los ejemplares menores (r=-0.94, p<0.001) siendo tolerada por los mayores (r=0.72, p<0.05). La carga promedio del pie disminuye con la altura del oleaje (r=-0.93, p<0.001). CONCLUSIONES: Con elevada agregación los ejemplares mayores emigran hacia substratos de difícil conquista por los menores, que están limitados por la acción mecánica del medio. La disminución de la carga del pie facilita la dispersión de los individuos

Novel interactions between K+ channels and scorpion toxins.

K(+) channels are macromolecules embedded in biological membranes, where they play a key role in cellular excitability and signal transduction pathways. Knowledge of their structure should help improve our understanding of their function and lead to the design of therapeutic compounds. Most pharmacological and structural characteristics of these channels have been elucidated by using high-affinity channel blockers isolated from scorpion venoms. Recent data on the three-dimensional structures of K(+) channels and novel scorpion toxins suggest a variety of novel interacting modes of these channels and toxins, which should help increase our understanding of the K(+) channel structure-function relationship.

Two novel toxins from the Amazonian scorpion Tityus cambridgei that block Kv1.3 and Shaker B K(+)-channels with distinctly different affinities.

Two novel toxic peptides (Tc30 and Tc32) were isolated and characterized from the venom of the Brazilian scorpion Tityus cambridgei. The first have 37 and the second 35 amino acid residues, with molecular masses of 3,871.8 and 3,521.5, respectively. Both contain three disulfide bridges but share only 27% identity. They are relatively potent inhibitors of K(+)-currents in human T lymphocytes with K(d) values of 10 nM for Tc32 and 16 nM for Tc30, but they are less potent or quite poor blockers of Shaker B K(+)-channels, with respective K(d) values of 74 nM and 4.7 microM. Tc30 has a lysine in position 27 and a tyrosine at position 36 identical to those of charybdotoxin. These two positions conform the dyad considered essential for activity. On the contrary, Tc32 has a serine in the position equivalent to lysine 27 of charybdotoxin and does not contain any aromatic amino acid. Due to its unique primary sequence and to its distinctive preference for K(+)-channels of T lymphocytes, it was classified as the first example of a new subfamily of K(+)-channel-specific peptides (alpha-KT x 18.1). Tc30 is a member of the Tityus toxin II-9 subfamily and was given the number alpha-KT x 4.4.