Effect of phosphocreatine on the lysophosphoglyceride levels in total ischemia of the rat myocardium

The phospholipid composition of the crude plasma membrane fraction of Langendorff perfused rat hearts has been studied. The effect of phosphocreatine (PCr) and 3-phosphono-2-imino-1-methyl-4-oxoimidazolidine (PIMOI) on lysophosphoglycerides (LPG) level in this fraction isolated from hearts that were totally ischemic for 8 minutes, has been examined. The absolute and relative contents of LPG were significantly increased in ischemic hearts: the lysophosphatidylcholine content was elevated by 94% and that of lysophosphatidylethanolamine--by 77%. Accumulation of these LPG in ischemic myocardium was completely inhibited in the presence of 10 mM PCr or PIMOI in the perfusate. LPG may play a key role in the destruction of sarcolemma. Therefore, these data allow to assume that the protective effect of PCr and PIMOI on the sarcolemma of ischemic myocardium may be the result of their influence on the phospholipid metabolism in the ischemic region of the heart.     

Effect of calcium on RNA and protein synthesis in the hypertrophied myocardium.

Myocardial protein synthesis was elevated 7 days after rats were subjected to experimental aortic outflow obstruction. Although RNA synthesis was not increased at this time, RNA concentration was elevated and may have provided for the observed increase in protein synthesis. A possible basis for the persistence of the high RNA levels was a decrease in the degradation of RNA. The increase in intracellular calcium observed in hypertrophied tissue may be involved in the maintenance of RNA concentration and in the increased rate of protein synthesis.     

Effect of RNA secondary structure and modified bases on the inhibition of trypanosomatid protein synthesis in cell free extracts by antisense oligodeoxynucleotides.

Every messenger RNA from leishmanias and trypanosomes has at its 5' end a conserved region termed the mini-exon sequence which, however, varies from species to species. In a systematic study mRNAs from Trypanosoma brucei, Trypanosoma vivax, and Leishmania enriettii were translated in cell-free extracts in the presence of oligodeoxynucleotides complementary to part of the mini-exon sequence. The affinity of the same oligonucleotides for target and non-target mRNAs was determined by thermal elution of filter-bound complexes showing that the critical temperature of half-dissociation of the complexes was linearly related to log (l + x), where l is the length of the oligomer and x its G + C content. A few oligomers exhibited a lower Tc value than expected which was ascribed to the presence of modified RNA bases or to the existence of a hairpin structure in the L. enriettii mini-exon. In most cases the efficiency of translation inhibition by the oligonucleotides was clearly correlated to their affinity for the target RNA. The modified bases weakened the inhibition of protein synthesis by oligonucleotides complementary to these regions.     

Effect of histones on cell permeability, protein and RNA synthesis and RNA stability in Aerobacter cloaceae]

The histones of calf thymus were found to change the permeability of the cells of Aerobacter cloaceae, without producing any noticeable effect on their viability. Concomitant depolymerization of the cellular RNA indicates destruction of the ribosomes. The increased synthesis of RNA in interpreted as a manifestation of reparatory processes. Protein synthesis, virtually unaffected in the resting cells, was inhibited to some extent in the growing culture treated with histones. Some considerations concerning the mode of action of histones at the intracellular level are presented.     

Effect of vitamin E an actinomycin D on protein and RNA synthesis in rat liver

In vitro experiments showed that RNA synthesis intensity in the rat liver with E-hypovitaminosis decreases considerably while the level of the labelled precursors incorporation into protein does not differ from the norm. Under conditions of E-hypovitaminosis the inhibitory effect of actinomycin D on the RNA synthesis is pronounced more clearly as compared to the norm. In the case of the E-hypovitaminous rate liver chyme preincubation with alpha-tocopherol there is no inhibitory effect of actinomycin D on the protein biosynthesis.     

Effect of alpha-isopropylmalate on the synthesis of RNA and protein in Neurospora

Summary The leu-3/-IPM (-isopropylmalate) regulatory system, previously shown to control several genes of leucine, isoleucine, valine, and histidine biosynthesis, appears likely to be involved also in the regulation of overall RNA and protein synthesis in Neurospora. Upon addition of -IPM the synthesis of all major species of stable RNA was found to be transiently inhibited by approximately 50%. A similar reduction was observed in overall protein synthesis. The inhibition was dependent in both cases on a functional leu-3 gene product, in conformance with previously established patterns of -IPM dependent gene regulation. The overt resemblance of the phenomenon described here to the stringent response of bacteria is noted but neither the mechanism of inhibition nor the precise role of -IPM in the process has been established.     

ATP synthesis kinetics and mitochondrial function in the postischemic myocardium as studied by 31P NMR

The effects of ischemia on mitochondrial function and the unidirectional rate of ATP synthesis (Pi----ATP rate) were studied using a Langendorff-perfused heart preparation and 31P NMR spectroscopy. There was significant postischemic depression of mechanical function assessed as the heart rate pressure product, and the myocardial oxygen consumption rate at a given rate pressure product was elevated. Experiments performed on glucose- and pyruvate-perfused hearts demonstrated the presence of a large contribution to the unidirectional Pi----ATP rate catalyzed by glyceraldehyde-3-phosphate dehydrogenase and phosphoglycerate kinase. This rate was much greater than the maximal glucose utilization rate in the myocardium, demonstrating that the glyceraldehyde-3-phosphate dehydrogenase/phosphoglycerate kinase reactions are near equilibrium both before and after ischemia. In the pyruvate-perfused postischemic hearts, the glycolytic contribution was eliminated and the net rate of ATP synthesis by oxidative phosphorylation was measurable. Despite the reduced mechanical function and increased myocardial oxygen consumption rate, the ratio of the net rate of ATP synthesis by oxidative phosphorylation to oxygen consumption rate (the P:O ratio) was not altered subsequent to ischemia (2.34 +/- 0.12 and 2.36 +/- 0.09 in normal and postischemic hearts, respectively). Therefore, mitochondrial uncoupling cannot be the cause of postischemic depression in mechanical function; instead, the data suggest the existence of ischemia-induced inefficiency in ATP utilization.     

Norepinephrine of the rat myocardium during repeated ischemia

Character of tissue changes as well as their reversibility could vary depending on the duration of myocardial ischemia. Long (over 30 min) ischemia leads to a massive release of myocardial interstitial norepinephrine. We tried to investigate changes in the myocardial sympathetic system produced by a relatively long episode of ischemia-repeperfusion. Myocardial norepinephrine has been collected by means of microdialysis probe during repeated occlusions of the left descending coronary artery. It was shown that long episode of occulusion-reperfusion resulted in suppression of massive norepinephrine release in response to second (test) occlusion. The features of norepinephrine release during successive occlusions make it possible to associate this process with the reversibility of the ischemic tissue damages.