Relationship between Intracellular Ca2+ Store and Protein Kinase C in Agonist-Induced Contraction of Hypertensive Rat Aortae

The roles of intracellular Ca2+ store and protein kinase C (PKC) in vascular contractile responses independent of Ca2+ influx were studied using aortic rings from spontaneously hypertensive rat (SHR) and Wistar-Kyoto rat (WKY). The functional sizes of agonist-sensitive intracellular Ca2+ store were estimated as the peak response to agonist after PKC inhibition with calphostin C (Cal-C), a PKC inhibitor. The participation of PKC in 5-hydroxytryptamine-, phenylephrine-, and endothelin-1 (ET-1)-induced contractions in aortae of SHR was equal to, or greater than that in WKY. In contrast, compared with WKY, SHR aortae possessed a greater size of endothelin-1-sensitive Ca2+ store, a similar size of 5-hydroxytryptamine-sensitive Ca2+ store, and a smaller size of phenylephrine sensitive Ca2+ store. Based on these data, both PKC activation and functional size of intracellular Ca2+ store differ between SHR and WKY and these differences are selective among agosists.