Mitochondrial damage as a mechanism of cell injury in the killing of cultured hepatocytes by tert-butyl hydroperoxide

The killing of cultured hepatocytes by tert-butyl hydroperoxide (TBHP) occurs by different mechanisms depending on the presence or absence of the antioxidant N,N'-diphenylphenylenediamine (DPPD). In either situation there is evidence of mitochondrial damage. The mitochondrial inner membrane potential is lost, a result determined by the release from the cells of the lipophilic cation [3H]triphenylmethylphosphonium (TPMP+). Deenergization of the mitochondria is accompanied by a loss of ATP. Oligomycin reduced ATP stores without release of TPMP+ or without effect on the viability of the hepatocytes over the same time course that TBHP killed the majority of the cells. Monensin, a H+/Na+ ionophore, potentiated the toxicity of tert-butyl hydroperoxide in the presence or absence of DPPD. By contrast, extracellular acidosis reduced the toxicity of tert-butyl hydroperoxide in the presence or absence of DPPD. Neither monensin nor extracellular acidosis affected the metabolism of tert-butyl hydroperoxide, the release of TPMP+, or the extent of the peroxidation of cellular lipids. These data document the presence of mitochondrial damage in hepatocytes intoxicated with TBHP in both the presence and absence of DPPD. Furthermore, the potentiation by monensin is readily explained by the proposal that mitochondrial deenergization is accompanied by an intracellular acidosis. Such acidosis tends to delay the development of lethal cell injury. The protective effect of extracellular acidosis supports this interpretation.     

Influence of neuroendocrine shifts in the pubertal period on the working memory operation in adolescents

It was found that the volume of working memory in adolescents at the initial pubertal stages (II–III) was lower than in adults. Analysis of the event-related potentials (ERPs) in various cortical areas in adolescents when they compared two successive pictures revealed specific features of neurophysiological mechanisms of visual working memory at the early pubertal stages. As compared to adult subjects, the adolescents were characterized by longer latencies and higher amplitudes of the early components of the ERPs. Certain differences were revealed in the functional organization of working memory both at the stages of stimulus fixation and in its comparison with the current information.     

Improved bacterial recovery by membrane filters in the presence of food debris.

In the absence of food debris, m-FC agar counts of Escherichia coli on Oxoid Nuflow membrane filters (Oxoid Canada Inc., Nepean, Ontario, Canada) were lower than the corresponding surface plate counts. For seven food types tested, recovery of E. coli improved with increasing thickness of food debris on the membrane filter, and mats thicker than 0.5 micron protected the organism completely.     

Localization of voltage-sensitive calcium channels along developing neurites: their possible role in regulating neurite elongation

Calcium action potentials were extracellularly recorded from growth cones of differentiated N1E-115 neuroblastoma cells maintained in monolayer cultures. Extracellular recordings along the neurites suggest that voltage-activated Ca²⁺ channels are less abundant in the processes than in the growth cones. In order to investigate if Ca²⁺ entry into the growth cone plays a role in the regulation of neurite growth, we studied the morphological changes induced by experimental conditions which permit calcium entry. Cells were depolarized either by 30 mM potassium (for 10–60 min) or by stimulating the soma (for 20–120 min) with an intracellular electrode. Morphological changes in individual cells were followed by means of time-lapse video recordings. In more than 60% of the experiments, steady-state potassium depolarization induced a pronounced increase of 20–120% in the area of the growth cone. This was frequently associated with neurite elongation. However, such changes could not be detected in the presence of Cd²⁺ concentrations which block the Ca²⁺ channels. Similar results were obtained in the presence of 2 μM of the Ca²⁺ ionophore A-23187 or when the cells were repetitively stimulated (0.2 Hz) in a medium containing 10^?6M TTX and 15 mM TEA. Local microapplication, directly onto single growth cones, of a depolarizing solution containing 5 mM Ca²⁺ also led to similar observations. Scanning electron microscopy indicated that the depolarized growth cone membranes were flattened and contained markedly more rounded protuberances relative to control cultures. Our results indirectly suggest that Ca²⁺ entry might be a trigger in the process of neurite elongation.     

Comparative characteristics of the ultrastructure of the causative agents of glanders and melioidosis]

The authors examined the ultrastructure of the causative agents of glanders and melio idosis. It was revealed that the structure of their cell wall and of the cytoplasmic membrane was characteristic of Gram negative bacteria. The cytoplasm of both types of the causative agents showed the presence of ribosomes, membrane structure, nucleoid, and also osmiophilic and osmiophobic inclusions.     

Induction by an hepatic carcinogen, 1-nitroso-5,6-dihydrouracil, of single and double strand breaks of liver DNA with rapid repair

The nitrosoureas derived from 3 naturally occurring ureides were administered to rats and the velocity sedimentation of hepatic DNA in alkaline and neutral sucrose gradients determined. The potent hepatocarcinogen 1-nitroso-5,6-dihydrouracil induced apparent double strand as well as single strand breaks in liver DNA within 30 minutes. This damage seemed to be repaired within 4 hours. In contrast, 1-nitrosohydantoin and δ-nitroso-L-citrulline, neither of which are known hepatocarcinogens, did not modify the velocity sedimentation of hepatic DNA.     

Enzymatic S-de-ethylation and the mechanism of S-dealkylation.

An NADPH- and oxygen-dependent enzymatic system responsible for the formation of acetaldehyde from ethylthioethers is present in the 9000 g supernatant fraction of rat liver. This system appears to be quite similar to the one responsible for the formation of formaldehyde from methylthioethers. Although both of these systems appears to be microsomal mixedoxidase systems, several anomalous findings regarding the mechanism of microsomal S-dealkylation have been observed and have led us to the conclusion that the mechanism of this reaction is more complex than originally believed. A scheme is postulated by which an enzyme in the soluble fraction causes microsomal sulfoxidation of alkylthioethers to alkylsulfoxides, followed by metabolism of the alkylsulfoxides to aldehydes.