Abstract
In ventricular myocytes, α1-adrenoceptor stimulation (α1ARS) increases L-type Ca2+ current (ICa,L) observed with perforated patch clamp recording. We previously showed that Ca2+/calmodulin-dependent protein kinase II (CaMKII) inhibition with KN-93 significantly blocked the potentiation of ICa,L by α1ARS. However CaMKII involvement in α1-adrenoceptor mediated modulation of ICa,L in mammalian ventricular myocytes and the mechanism of ICa,L potentiation during α1ARS are not been fully investigated. The purpose of this study is to clarify the role of CaMKII in the regulation of ICa,L during α1ARS. In Western immunoblotting analysis, phenylephrine significantly increased the amount of autophosphorylated CaMKII (p-CaMKII) and this increase was completely blocked by KN-93. We also investigated the changes in subcellular localization of p-CaMKII using immunofluorescence microscopy and immunoelectron microscopy. Before α1ARS phospho-CaMKII was exclusively located just beneath the surface plasma membrane (plasmalemma). But after α1ARS, it was localized close to sarcolemmal invaginations called transverse-tubules (T-tubules) where L-type Ca2+ channels highly exist. These findings strongly support the results of our electrophysiological experiments and we conclude that 1) CaMKII which exists near T-tubules was activated by α1ARS and 2) CaMKII activation directly potentiates ICa,L in rat ventricular myocytes. [Jpn J Physiol 55 Suppl:S93 (2005)]
