A study of chlorophyll-like and phycobilin pigments in the C endosymbiont of the apple- snail Pomacea canaliculata

Pigments present in the brown-greenish C morph of an intracellular endosymbiont of Pomacea canaliculata were investigated. Acetone extracts of the endosymbiotic corpuscles showed an absorption spectrum similar to that of chlorophylls. Three fractions obtained from silica gel column chromatography of the acetone extracts (C I, C II and C III), were studied by positive ion fast atom bombardment-mass spectrometry (FAB-MS) and hydrogen-nuclear magnetic resonance (H-NMR). Results indicated the presence of (1) a sterol in the yellow colored C I fraction; (2) a mixture of pheophorbides a and b in the major green fraction, C II; and (3) a modified pheophorbide a in the smaller green fraction, C III. Aqueous extracts of the C endosymbiont did not show evidence of the occurrence of C-phycocyanin, allophycocyanin or phycoerithrin (light absorption, fluorescence emission, and electrophoresis of the protein moieties) while cyanobacterial cells (Nostoc sp.) showed evidence of C-phycocyanin and allophycocyanin. The possible phylogenetic and functional significance of the pigments present in the C endosymbiont is discussed.

Lipids analysis in hemolymph of African giant Achatina fulica (Bowdich, 1822) exposed to different photoperiods / Análises dos lipídeos no gigante africano Achatina fulica (Bowdich, 1822) expostos a diferentes fotoperíodos

The influence of different photophases (0, 6, 12, 18 and 24 hours) on the triglycerides and total cholesterol contents in the hemolymph of A. fulica was evaluated, since there is no information in the literature about the influence of this factor on lipids metabolism in mollusks. After 2 and 4 weeks of exposure the snails were dissected. The cholesterol content at the 2nd and 4th weeks post exposure only varied significantly in the groups exposed at 24 hours and 0 hour of photophase, respectively. Probably, such increase may be a result of a rise in cholesterol biosynthesis and/or remodelling of cell membranes. There were no significant differences among the content of triglycerides in the snails exposed to 6, 12, 18 and 24 hours of photophase during two weeks. The snails exposed to intermediate photophase (6 and 12 hours) had the triglycerides content increased, ranging over values near to those observed in the group exposed to 0 hour. Results showed that triglycerides metabolism in A. fulica are more influenced by photoperiod than cholesterol metabolism. A negative relation is maintained between the triglycerides content in the hemolymph and the different photophases, with lower mobilisation of triglycerides under shorter photophases.

A influência de diferentes fotofases (0, 6, 12, 18 e 24 horas) sobre os conteúdos de triglicerídeos e de colesterol total na hemolinfa de A. fulica foi avaliada, uma vez que não há na literatura informações sobre a influência deste fator sobre o metabolismo de moluscos. Após 2 e 4 semanas de exposição, os moluscos foram dissecados. O conteúdo de colesterol até a 2ª e 4ª semanas pós exposição somente variou significativamente nos grupos expostos a 24 horas e 0 horas de fotofase, respectivamente. Provavelmente, tal aumento pode ser resultado de uma elevada biossíntese de colesterol e/ou remodelamento de membranas celulares. Não houve diferenças significativas entre o conteúdo de triglicerídeos nos moluscos expostos a 6, 12, 18 e 24 horas de fotofase até a segunda semana. Os moluscos expostos a fotofases intermediárias (6 e 12 horas) tiveram o conteúdo de triglicerídeos aumentados, levando seus valores próximo àqueles observados para o grupo exposto a 0 hora de fotofase. Isto mostra que o metabolismo de triglicerídeos em A. fulica é mais influenciado pelo fotoperíodo do que o metabolismo de colesterol. Uma relação negativa é mantida entre o conteúdo de triglicerídeos na hemolinfa e as diferentes fotofases, com menor mobilização de triglicerídeos sob fotofases curtas.

Storage excretion in the Indian apple snail, Pila globosa (Swainson), during aestivation.

Uric acid accumulates in several tissues of the Indian apple snail, P. globosa, during aestivation. This accumulation is particularly high in the foot muscle and reproductive organs. Since the kidney, a tiny organ in the snail, has only a limited capacity to store uric acid, extrarenal tissues are used as storage depots of uric acid during aestivation. It is suggested that the aestivating snail, faced with a cleidoic situation, resorts to storage excretion, a phenomenon well documented in insects.

Hydrogen peroxide as a tool for studying oxidative stress in the heart

Hydrogen peroxide (H2O2) was observed to depolarize the frog sartorius muscle and promote rhythmic contraction of frog cardiac ventricular rings or their contracture. This last effect was sodium-dependent. H2O2 perfused or injected into the aorta of the isolated rat heart induces a positive inotropic effect (with cardiac arrhythmias such as extrasystolic potentiations) followed by deoression of contractility or cardiac contractures, according to the dose employed. The last effects is similar to the "stone heart"observed in the reperfusion injury and may be ascribed to lipoperoxidation (LPO) of the membrane lipids, to protein damage, to reduction in the ATP level and/or to cardioactive compounds liberated by LPO. Besides its direct effect on the ATP level, H2O2 would react with iron ions to produce hydroxyl radicals that attack the cellular membranes. Deferoxamine, an iron chelator and scavenger of hydroxyl radicals, reduced the contractures induced by H2O2. Perfusion with H2O2 increased the LPO of cardiac homogenates measured by chemiluminescence, oxygen uptake and malonaldehyde formation. The fall in ATP levels and the LPO would result in calcium overload of the cardiac fibers and contracture ("stone heart"). The 45Ca uptake was increased by incubation of cardiac strips with H2O2. Previous perfusion of the isolated rat heart with nifedipine or indomethacin reduced the H2O2 cardiac contracture. Vitamin A, a quencher of singlet oxygen liberated during LPO, reduces the H2O2 cardiac contractures and also LPO. Gradual physical exercises, besides increasing the oxygen consumption, protected the heart from oxidative stress. The experimental production of hypothyroidism protected the heart against the H2O2 oxidative stress. The hearts of rats submitted to hypertension with high renin levels showed increased LPO, measured by chemiluminescence and oxygen uptake, indicating that this condition may be produced by oxygen species or causes their production. All these findings give support to the idea that the ischemia-reperfusion injury is an active oxygen species associated disorder that induces cardiac stiffness or contractures that would be produced by calcium overload. Thus, H2O2 may be useful for inducing experimental oxidative stress in the heart and for studying its oxidative status in physiological and pathological situations.