부산대학교 도서관

Key points L-type Ca2+ channels are inactivated by an increase in intracellular [Ca2+], known as Ca2+-dependent inactivation (CDI), and are inhibited by Ca2+ released from the sarcoplasmic reticulum (SR), known as release-dependent inhibition (RDI)., RDI was greatly enhanced by the removal of Na+-Ca2+ exchange (Incx), and attenuated by blocking Ca2+ release from the sarcoplasmic reticulum (SR), and abolished by Ca2+ chelator., We analysed the role of ICaL, SR and Incx and found Incx prevented CDI by controlling [Ca2+] in the junctional subsarcolemmal space ([Ca2+]JSS)., With previously developed model and the addition of Ca2+ binding kinetics of L-type Ca2+ channels (ICaLs), we successfully reproduced CDI and RDI., From this simulation, we found Incx actively participated in controlling CDI by the regulation of [Ca2+]JSS and by controlling SR Ca2+ refilling., Abstract L-type Ca2+ channels (ICaLs) are inactivated by an increase in intracellular [Ca2+], known as Ca2+-dependent inactivation (CDI). CDI is also induced by Ca2+ released from the sarcoplasmic reticulum (SR), known as release-dependent inhibition (RDI). As both CDI and RDI occur in the junctional subsarcolemmal nanospace (JSS), we investigated which factors are involved within the JSS using isolated cardiac myocytes from the main pulmonary vein of the rabbit. Using the whole-cell patch clamp technique, RDI was readily observed with the application of a pre-pulse followed by a test pulse, during which the ICaLs exhibited a decrease in peak current amplitude and a slower inactivation. A fast acting Ca2+ chelator, 1,2-bis(o-aminophenoxy)ethane- N, N, N′, N′-tetraacetic acid (BAPTA), abolished this effect. As the time interval between the pre-pulse and test pulse increased, the ICaLs exhibited greater recovery and the RDI was relieved. Inhibition of the ryanodine receptor (RyR) or the SR Ca2+-ATPase (SERCA) greatly attenuated RDI and facilitated ICaL recovery. Removal of extracellular Na+, which inhibits the Na+-Ca2+ exchange (Incx), greatly enhanced RDI and slowed ICaL recovery, suggesting that Incx critically controls the [Ca2+] in the JSS. We incorporated the Ca2+-binding kinetics of the ICaL into a previously published computational model. By assuming two Ca2+-binding sites in the ICaL, of which one is of low-affinity with fast kinetics and the other is of high-affinity with slower kinetics, the new model was able to successfully reproduce RDI and its regulation by Incx. The model suggests that Incx accelerates Ca2+ removal from the JSS to downregulate CDI and attenuates SR Ca2+ refilling. The model may be useful to elucidate complex mechanisms involved in excitation-contraction coupling in myocytes. [ABSTRACT FROM AUTHOR]