Lysosomal stability in Oreochromis mossambicus (Peters) on exposure to surfactants.

The three commonly used surfactants viz. anionic sodium dodecyl sulfate (SDS), cationic cetyl tri methyl ammonium bromide (CTAB) and non-ionic triton X-100 were toxic even at sub lethal levels (1 ppm for 30 days) to 0. mossambicus. Lysosomal stability index (LSI) was lowest in triton-exposed animals in vitro. In vivo, CTAB was the most toxic. SDS, the anionic surfactant was the least toxic. The possible role of surfactant structure, critical micellar concentration (CMC) and metabolism in influencing the toxicity is discussed and mechanism of action via membrane lipid peroxidation is suggested.

Apoptogenic effect of the lipophilic o-naphthoquinone CG 10-248 on rat hepatocytes: light and electron microscopy studies

CG 10-248 (3,4-dihydro-2,2-dimethyl-9-chloro-2H-naphtho[1,2b]pyran-5,6-dione; CG-NQ), a beta-lapachone analogue, modified the ultrastructure of rat hepatocytes, as demonstrated by light and electron microscopy. After 4 h incubation with 100 microM CG-NQ, the following effects were observed: (a) nuclear chromatin condensation; (b) chromatin fragmentation; (c) displacement of mitochondria, concentrated around the nucleus; (d) disruption or expansion of mitochondrial outer or inner membranes, respectively; (e) displacement and alteration of endoplasmic reticulum (rough and smooth); (f) decrease of microvilli; (g) blebbing of plasma membrane and production of apoptotic bodies formed by folding of plasma membrane fragments around mitochondria or peroxysomes; and (h) production of hydrogen peroxide. Expression of such effects varied according to hepatocyte samples and taken together strongly support an apoptotic action of CG-NQ dependent on reactive oxygen species.

Mitochondrial oxidative damage promoted by a synergism betweem Ca2+ and prooxidants: inner membrane permeabilization and mtDNA breakage

Oxidative damage of mitochondria induced by a synergism between Ca2+ and prooxidants is mediated by the attack of mitochondria-generated reactive oxygen species to membrane proteins, lipids and DNA. This results in mitochondrial DNA fragmentation, lipid peroxidation and oxidation of vicinal protein thiols producing high molecular weight membrane protein aggregates. The membrane protein alterations lead to a condition called mitochondrial membrane permeability transition, characterized by formation of nonspecific membrane protein pores sensitive to cyclosporin A, EGTA, dithiothreitol, Mg2+ and ADP. We propose that these alterations are related to the mechanisms by which cells are killed by a series of toxins, xenobiotics or pathological conditions such as prolonged hypoxia or ischemia/reperfusion.

Lipid peroxidation in hepatic microsomal membranes isolated from mice in health and in experimental leishmaniasis.

Normal hepatic microsomal membranes when exposed in vitro to different free radicals, cause membrane damage by lipid peroxidation which could be monitored by the analysis of malonaldehyde formation and measurement of membrane microviscosity. Lipid peroxidation in vivo, when examined in hepatic microsomal membranes in experimental Leishmaniasis, reveals a direct relationship between membrane microviscosity and the extent of lipid peroxidation. Scavengers of free radicals and peroxides such as superoxide dismutase (SOD) for O2.-, mannitol for (OH.) and catalase for H2O2 in modest amounts were used for preventing the membrane damage caused by lipid peroxidation.

Effect of theophylline on binding of delta-9-tetrahydrocannabinol with mammalian neuronal and non-neuronal membranes.

Delta-9-tetrahydrocannabinol (THC) (1.6 x 10(-6)-13.33 x 10(-6) M) binds to neuronal and non-neuronal subcellular membranes in a biphasic manner. Its binding to neuronal membranes occur in the following order synaptosome > myelin > brain microsome and brain mitochondria. Unlike brain membranes binding of delta-9-THC is greater with liver microsome than liver mitochondria. Irrespective of membranes theophylline (Th) (11.0 x 10(-6) and 550.0 x 10(-6) M) increases the binding of delta-9-THC by exposure of more number of delta-9-THC binding sites on the subcellular membranes without affecting its binding affinity. Failure of Th (11.0 x 10(-6)-550.0 x 10(-6) M) to increase the binding of delta-9-THC (1.6 x 10(-6)-13.33 x 10(-6) M) in solubilized membranes suggests the involvement of membrane lipid in the Th-induced enhancement of delta-9-THC binding.

Calcium homeostasis in Trypanosoma cruzi

By using the fluorescent Ca2+ indicator fura 2, submicromolar levels of intracellular Ca2+ have been detected in Trypanosoma cruzi different stages. The intracellular transport mechanisms involved in maintaining Ca2+ homeostasis in T. cruzi have been characterized by measuring Ca2+ transport in digitonin-permeabilized cells. Two intracellular calcium transport systems have been detected. Ca2+ uptake by the mitochondria occurs by an electrophoretic mechanism, is inhibited by antimycin A, FCCP, and ruthenium red, and stimulated by respiratory substrates, phosphate and acetate. This pool has a high capacity and low affinity for Ca2+ and is able to buffer external Ca2+ at concentrations in the range of 0.6-0.7 microM. Ca2+ uptake by the endoplasmic reticulum is inhibited by high concentrations of vanadate and anticalmodulin agents, and stimulated by ATP. This pool has a low capacity and a high affinity for Ca2+ and is able to buffer external Ca2+ at concentrations in the range of 0.05-1.0 microM. In addition, calmodulin has been purified from T. cruzi epimastigotes and shown to stimulate the homologous plasma membrane Ca(2+)-ATPase and cyclic-AMP phosphodiesterase. The gene encoding this protein has been cloned and sequenced and shown to have a great homology to mammalian calmodulin. The role of the plasma membrane of T. cruzi in the regulation of [Ca2+]i has been studied using fura 2-loaded epimastigotes or plasma membrane vesicles prepared from epimastigotes. Plasma membrane vesicles transport Ca2+ in the presence of Mg2+ and have a high affinity, vanadate-sensitive (Ca(2+)-Mg2+)-ATPase with an apparent Km for free Ca2+ of 0.3 microM.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of aliphatic amine 1,4-diazobicyclo (2,2,2) octane-induced stimulation of beet spinach thylakoid electron transport.

Electron transport activity of beet spinach thylakoids was enhanced in the presence of aliphatic amine, DABCO (1,4-diazobicyclo (2,2,2) octane), a hydrophilic proton trapping agent. The extent of stimulation was pH-dependent and similar to the effect of the uncoupler ammonium chloride on electron transport. The stimulation of whole-chain (H2O-->MV) electron transport activity was observed only at high (rate-saturating) light intensity. The light-induced proton uptake coupled to electron transport of thylakoid was also arrested by DABCO, suggesting that DABCO uncouples thylakoid phosphorylation by proton trapping.

Membrane instability in respiring mitochondria: role of phosphate.

Metabolically-induced (spontaneous) high amplitude swelling of mitochondria has been shown to be due to a serial disruption of the mitochondrial membranes [D. Sambasivarao & V. Sitaramam (1985), Biochim Biophys Acta, 806, 195-209]. Phosphate- and arsenate-induced swelling was investigated in mitochondria to evaluate the role of phosphate transport in the instability created in the mitochondrial membranes. Phosphate-induced swelling in respiring mitochondria was similar to spontaneous swelling. Both represent essentially colloidal swelling due to the variable porosity induced in the inner membrane to polyols by respiration. Swelling of non-respiring mitochondria at high ammonium phosphate concentrations was, on the other hand, primarily due to high permeability to phosphate. This membrane instability created by phosphate transport in the surrounding lipid involves neither the endogenous nor the exogenous Ca2+.

Effect of defoliant (butiphose) on morpho-physiological properties and enzyme systems of natural membranes.

Butiphose (Tributyltritiophosphate, (C4H9S)3PO) a commonly used defoliant in cotton growing regions of USSR, caused extensive alterations in morphological features of erythrocyte and nuclear membranes and affected the permeability properties of rat liver mitochondrial membrane. It disrupted Ca2+ transport system and other energy dependent processes in mitochondria. A reduction in the activity of cytochrome-c-oxidase and NAD.H-oxidase was also observed.