CALCIUM-INDUCED CALCIUM-RELEASE IN EGTA-SKINNED AORTIC STRIPS FROM GENETICALLY HYPERTENSIVE AND NORMOTENSIVE RATS

The release of Ca-45 induced by Ca2+ was studied in genetically hypert ensive (SHR) and normotensive (WKY) rats using EGTA-skinned aortic str ips. Strips preloaded with Ca-45 (pCa 6.6) were desaturated at 5 mM of EGTA. A slow component of the washout in aorta from SHRs exhibited hi gher Ca content and a lower rate of Ca leak than that in aorta from WK Y rats. This slow component was stimulated during washing with 0.03, 0 .3, 1 or 10 mu M free Ca2+. The release of Ca-45 induced by Ca2+ proce eded at similar rates in preparations of the two strains. Compared to WKY aortic strips the stimulated efflux of Ca-45 was greater in SHR ao rtic strips due to the higher Ca content. About half of the release of Ca-45 induced by 1 mu M free Ca2+ during the first 6 minutes of stimu lation was blocked by 0.6 mM of ryanodine or 50 mu M of ruthenium red, thus identifying the sarcoplasmic reticulum as a source of Ca release . The results suggest that this intracellular storage of Ca in aorta f rom genetically hypertensive rats is relevant for the generation of hi gh levels of cytosolic Ca2