Proteiensintese in hartspierweefsel van die rot

Abstract

The object of this study was to investigate miocardial protein synthesis. Although it is known that ca++ stimulates protein synthesis there is some difference of opinion as to the exact site of action of the synthesis process. The different points of view on the Ca++ effect are membrane transport of amino acids versus a direct effect on translation. To clarify this point the effect of ca++ on protein synthesis was investigated. Albino rats were used in all experiments. The synthesis was examined by way of isolated polysomes in a cell free system as well as with heart tissue slices. It was determined that both, ca++ and Mg++, stimulate cardiac protein synthesis. This effect was not only present in experiments with tissue slices, but was even more significant during synthesis with isolated cardiac polysomes. It could further be shown that ca++ at low concentrations (1mM) maintained synthesis while Mg++ did not show the same effect. Magnesium ions, on the other hand, are responsible for a much larger total synthesis than ca++. An indication of the effect of ca++ on the stability of the polysome structure was obtained through sucrose gradient centrifugation. The deduction was made that ca++ ions are preferable for synthesis at low ionic concentrations, whereas Mg++ ions are

prefered for the stabilisation of the cell free system during the isolation procedure. To further evaluate the effect of ca++ on protein synthesis a correlation was drawn between ca++ transport and protein synthesis with the aid of two glycosides namely ouabain and digitoxin. It was determined that the inhibitory effect of these cardiac glycosides on protein synthesis could not be attributed to a disturbed production of energy in the cell. Possible explanations and a few practical applications of the observed results are given.