The relationship betweeen action potential duration and the rate of Ca²⁺ replenishment to the junctional sarcoplasmic reticulum in heart muscle of hypertensive rat

Abstract

To characterize Ca²⁺handling by the junctional sarcoplasmic reticulum (JSR) in heart muscle of hypertensive rat(SHR), we examined the time course of short-term mechanical restitution(STMR) after varying magnitude of twitch contraction with the papillary muscle of adult(20 weeks-old)SHR and age-matched control(WKY) and action potential duration at various stimulus frequencies. The slope of the STMR in WKY was independent of the magnitude of the preceding twitch and similar to that of SHR unless the preceding twitch was not so large as the rested state twitch. The slope decreased after the rested state twitch in SHR. The functions G(t) and H(t), representing the time courses of the JSR Ca²⁺ replenishment and release, respectively, were derived graphically from a family of the mechanical restitution curves for the both strains. The action potential duration as measured at its half width was significantly greater in SHR than WKY(p <0.005). Both a time to peak tension and a half relaxation time were significantly longer in SHR than WKY(p <0.0001). The result suggests slower Ca²⁺ replenishment to the JSR in SHR than WKY irrespective of the longer action potential in the former than the latter. [J Physiol Sci. 2006;56 Suppl:S127]