Interacção de catiões com membranas do músculo e do cérebro

Abstract

The Ca2+ stimulated ATPase activity of sarcoplasmic reticulum ( SR ) is activated after a short period of preincubation at temperatures between 40 and 450C, but for temperatures higher than 480C pronounced denaturation is observed. Heat denaturation is decreased if Mg2+ or K+ are present which is attributed to stabilization by cations of the ATPase Ca2+ transport coupled to the ATPase activity in SR was followed by using the chlorotetracycline ( CTC ) fluorescense technique, and it is concluded that the Ca2+ accumulated in the presence of ATP is mostly bound to the membranes. The fluorescence of CTC was also utilized to follow the interaction of Ca2+ with brain membranes, and the technique was found to be useful to monitor the binding and release of Ca2+ in synaptosomes and other brain membrane fractions. The passive permeability of synaptosomes to electrolytes and non-electrolytes is temperature dependent. Furthermore, the fluxes of Ca2+, Sr2+ and Mg2+ were studied and the results suggest that the efflux of Ca2+ in synaptosomes is induced selectively by Na+, which is a major mechanism responsible for the regulation of Ca2+ in the nerve cell.