COMPARISON OF SARCOPLASMIC-RETICULUM CHARACTERISTICS IN AORTIC SMOOTHAND VENTRICULAR MUSCLES USING CHEMICALLY SKINNED PREPARATIONS

The active Ca2+ transport and the kinetics of Ca2+ efflux in sarcoplas mic reticulum (SR) of skinned aortic smooth muscle cells are compared with those in SR of skinned ventricular muscle cells. Ca-45 uptake was measured at pCa 6.6 in the presence of 10 mM of K oxalate from 2 to 3 0 min. Unstimulated and Ca2+ stimulated Ca2+ efflux were assessed on C a2+ desaturation curves performed in skinned cells preloaded with Ca-4 5 in the absence of K oxalate. Results demonstrate that SR in aortic s mooth muscle cells compared with SR in ventricular cells has : a) 2 ti mes lower initial phase of Ca2+ uptake, b) 10 times lower enclosed vol ume, c) higher rate of unstimulated Ca2+ efflux and d) higher plus mor e sustained release of Ca2+ induced by Ca2+. It is also proved that th e stimulated release of Ca2+ can be supressed by 0.6 mM of ryanodine i n aortic smooth muscle and by 50 muM of ruthenium red in ventricular m uscle. This work provides direct measurements of Ca2+ transport capaci ty and of Ca2+ release of in situ sarcoplasmic reticulum. It quantifie s the functional differences between vascular smooth and ventricular m uscles.