Physiological rates in different classes of sizes of Perna perna (Linnaeus, 1758) submitted to experimental laboratory conditions.

Physiological studies of the mussel Perna perna in Brazil are almost 30 years behind those of other, more exhaustively investigated species, such as Mytilus edulis. Little is known about the variations in physiological rates due to size and the consequences of maintaining P. perna in laboratory conditions. This work investigated the variations in respiration, clearance, excretion and absorption efficiency rates of P. perna, classified by size and acclimatized in a laboratory, monitoring the mussels respiration rates and biometry over a period of 30 days, in laboratory conditions. The respiration, clearance and excretion rates presented an allometric relation with the dry weight of the organisms, with b values of 0.66, 0.48 and 0.91 respectively. On the other hand, these same rates, when considered by weight (specific rates) showed a relationship that was inverse to the size of the organisms. Only the absorption efficiency was independent of the weight of the mussel. In terms of acclimatization, it was observed that it takes 10 days for the respiration rate of the mussel P. perna to stabilize in laboratory conditions, after which it follows a routine metabolism.

Physiological rates in different classes of sizes of Perna perna (Linnaeus, 1758) submmited to experimental loboratory conditions

O estudo da fisiologia dos mexilhões Perna perna no Brasil apresenta uma defasagem de aproximadamente 30 anos em relação a outras espécies mais exaustivamente investigadas como Mytilus edulis. O conhecimento acerca das variações das taxas fisiológicas em função do tamanho e as conseqüências da manutenção de P. perna em laboratório foram pouco estudadas. Neste trabalho, investigaram-se as variações das taxas de respiração, clareamento, excreção e a eficiência de absorção de P. perna aclimatados em laboratório em diferentes classes de tamanho, assim como foi realizado um acompanhamento de suas taxas respiratórias e de sua biometria ao longo de 30 dias de manutenção em condições laboratoriais. As taxas de respiração, clareamento e excreção apresentaram uma relação alométrica com o peso seco dos organismos, obtendo-se como valores de b de 0,66, 0,48 e 0,91 respectivamente. Por outro lado, estas mesmas taxas quando ponderadas pelo peso (taxas específicas) mostraram uma relação inversa com o tamanho dos organismos. A eficiência de absorção foi à única taxa que mostrou independência com o peso do mexilhão. Em termos de aclimatação, observou-se que o mexilhão P. perna leva 10 dias para estabilizar a sua taxa de respiração em laboratório, entrando em metabolismo de rotina.

Skin secretion of Siphonops paulensis (Gymnophiona, Amphibia) forms voltage-dependent ionic channels in lipid membranes

The effect of the skin secretion of the amphibian Siphonops paulensis was investigated by monitoring the changes in conductance of an artificial planar lipid bilayer. Skin secretion was obtained by exposure of the animals to ether-saturated air, and then rinsing the animals with distilled water. Artificial lipid bilayers were obtained by spreading a solution of azolectin over an aperture of a Delrin cup inserted into a cut-away polyvinyl chloride block. In 9 of 12 experiments, the addition of the skin secretion to lipid bilayers displayed voltage-dependent channels with average unitary conductance of 258 ± 41.67 pS, rather than nonspecific changes in bilayer conductance. These channels were not sensitive to 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid or tetraethylammonium ion, but the experimental protocol used does not permit us to specify their characteristics

Skin secretion of Siphonops paulensis (Gymnophiona, Amphibia) forms voltage-dependent ionic channels in lipid membranes.

The effect of the skin secretion of the amphibian Siphonops paulensis was investigated by monitoring the changes in conductance of an artificial planar lipid bilayer. Skin secretion was obtained by exposure of the animals to ether-saturated air, and then rinsing the animals with distilled water. Artificial lipid bilayers were obtained by spreading a solution of azolectin over an aperture of a Delrin cup inserted into a cut-away polyvinyl chloride block. In 9 of 12 experiments, the addition of the skin secretion to lipid bilayers displayed voltage-dependent channels with average unitary conductance of 258 +/- 41.67 pS, rather than nonspecific changes in bilayer conductance. These channels were not sensitive to 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid or tetraethylammonium ion, but the experimental protocol used does not permit us to specify their characteristics.

Variability of filtration and food assimilation rates, respiratory activity and multixenobiotic resistance (MXR) mechanism in the mussel Perna perna under lead influence.

The economic importance that multiculture is conquering in Santa Catarina State (South of Brazil) explains the crescent search for new coastal sites for farming. Physiological and biochemical studies of the mussel Perna perna are important to the establishment of methodologies for program assessment and environmental monitoring, allowing to infer about site quality and possible influences of xenobiotic agents on coastal areas. In order to evaluate effects caused by lead poisoning (1.21 mumol.L-1), the mussels were maintained at constant temperature (25 degrees C) and fed with Chaetoceros gracilis for 15 days. The control group was acclimatized in sea water 30@1000. At the end of this period time, physiological measurements were carried out along with statistic analysis for filtration rates, lead assimilation and overall respiratory activity. The mechanism of multixenobiotic resistance (MXR) was particularly evaluated in standardized gill fragments using rhodamine B accumulation and its quantification under fluorescence optical microscopy. Regarding the control group, results had shown that the mussels maintenance in a lead-poisoned environment caused higher filtration rates (1.04 and 2.3 and L.h-1.g-1; p < 0.05) and lower assimilation rates (71.96% and 54.1%, respectively). Also it was confirmed a lesser rhodamine B accumulation in the assays under influence of lead, suggesting that this metal induces the MXR mechanism expression in mussel P. perna. These results indicate that such physiological and biochemical alterations in the mussels can modify the energy fluxes of its metabolism, resulting in possible problems on the coastal systems used as cultivating sites.

Effects of catecholamines on the isolated aorta of the snake Bothrops jararaca

Effects of catecholamines in snakes have been examined using an aorta preparation isolated from Bothrops jararaca. Adrenaline, noradrenaline and isoprenaline produced dose-dependent contractions on this preparation. The relative potency was adrenaline > noradrenaline > isoprenaline. 2. Phentolamine displaced, to the right, the concentration-response curve of the three catecholamines tested, showing the presence of alpha-adrenoceptors in this preparation. 3. Isoprenaline has never produced a relaxation, even when the aorta was first contracted by BaCl2 and pretreated with phentolamine, indicating that beta-adrenoceptors are absent in this preparation. 4. In this Bothrops jararaca preparation, exclusively neuronal uptake was found, thus demonstrating that its existence was preserved during evolution.

Neuroendocrine regulation of osmotic and ionic concentrations in the hemolymph of the freshwater shrimp Macrobrachium olfersii (Wiegmann) (Crustacea, Decapoda).

Putative neuroendocrine mediation of osmotic and ionic responses to acute exposure to high salinity medium was investigated in the freshwater shrimp Macrobrachium olfersii (Wiegmann). Homogenates of supra-esophageal or thoracic ganglia, prepared from shrimps exposed to seawater of 21% S for 6 hr, were injected into the abdominal musculature of shrimps previously exposed to freshwater and subsequently exposed to either freshwater or seawater (21% S). Osmotic, sodium, chloride, potassium, magnesium, and calcium concentrations were determined in hemolymph samples removed by intracardiac puncture at time = 0, 1, 3, or 6 hr after homogenate application. Control shrimps were injected with filtered seawater, isosmotic to the hemolymph, and treated similarly. In control shrimps, the osmotic, Na+, Cl-, K+, Mg2+, and Ca2+ concentrations in the hemolymph increased (P less than or equal to 0.05) after 1-hr exposure to seawater. In shrimps injected with homogenates of supra-esophageal ganglion and exposed to seawater, osmotic and ionic concentrations in the hemolymph did not vary with exposure time; in injected shrimps exposed to freshwater, Na+, Cl-, K+, and Mg2+ concentrations decreased (P less than or equal to 0.05) with time. In shrimps injected with homogenates of thoracic ganglion and exposed to seawater, hemolymph osmotic, K+, and Mg2+ concentrations increased (P less than or equal to 0.05); Na+, Cl-, and Ca2+ concentrations remained unchanged. In injected shrimps exposed to freshwater, hemolymph osmotic concentration alone increased (P less than or equal to 0.05) after 1 hr, all other ionic concentrations remaining unchanged. These data suggest that neurofactors apparently located within the ganglia of the central nervous system of M. olfersii may alter the apparent ionic permeabilities of this shrimp, depending on the salinity characteristics of the external medium. The data support the notion that invasion of the freshwater biotope by estuarine crustaceans has necessitated the evolution of specific physiological mechanisms capable of compensating for the osmotic dilution and ion loss typically encountered by such organisms.

Lack of osmoregulation in Aplysia brasiliana: correlation with response of neuron R15 to osphradial stimulation.

The exposure of Aplysia brasiliana to dilute seawater (90 and 80%) caused an increase of the relative weight, which returned to the original values after a few hours. Both osmotic and chloride concentrations of the hemolymph decreased on exposure to 80 and 90% dilute seawater, and after 3-h exposure there were no differences between the hemolymph and external media osmotic and chloride concentrations. In contrast to the clear regulatory capabilities reported for A. californica, A. brasiliana cannot maintain the osmolality of its body fluid in dilute media. In A. californica, osphradial receptors and neuron R15 are apparently involved in this regulatory mechanism. Perfusion of osphradium of A. brasiliana with dilute seawater (95-80%) did not affect electrical activity of the bursting neuron R15; perfusion with 70 and 60% seawater caused a transient increase in the duration of the quiescent period. In contrast to the model established for A. californica, in A. brasiliana no relationship was found between exposure of the osphradium to dilute media and electrical activity in neuron R15, which is in accordance with the lack of an osmoregulatory mechanism in this species. Such differences may reflect inherent differences in salinity tolerance between the two species.

Cation composition and osmolality of the hemolymph of the terrestrial crab Gecarcinus lagostoma.

Hemolymph cation concentration and osmolality are reported for male and female specimens of the terrestrial crab Gecarcinus lagostoma collected on Trindade Island, Brazil (20 degrees 36'36" S and 29 degrees 19'26" W). Data for 9 female crabs weighing 133.7 +/- 25.4 g (mean +/- SD) were: osmolality, 816 +/- 85 mOsm/kg H2O; Na+, 357 +/- 55; K+, 7.9 +/- 0.8; Ca2+, 33.5 +/- 2.8 and Mg2+, 15.6 +/- 2.5 mEq/l. There were no significant differences between the female (N = 9) and male (N = 9) hemolymph parameters. The hemolymph Na+, K+, Ca2+ and Mg2+ concentrations and osmolality of G. lagostoma were higher (P less than 0.01) than those of U. cordatus, a previously studied Brazilian gecarcinid crab. These differences are probably due to the higher degree of terrestriality of G. lagostoma compared to U. cordatus.