Modulation of L-type Ca²⁺ channel by PKA requires CaM

Abstract

In cardiac myocytes Ca²⁺ entry into the cells through Ca²⁺ channels play a crucial role in excitation-contraction coupling. PKA is the most important regulatory factor of the Ca²⁺ channel. Although PKA enhances Ca²⁺ channel activity in whole-cell condition, such regulation is not seen in excised patches, suggesting that the PKA effect requires cooperation with other factors. To confirm this hypothesis, we have investigated a possible involvement of CaM in the PKA effect in guinea-pig cardiac ventricular myocytes. Our results showed CaM inhibitor chlorpromazine (CPZ) abolished the effect of 8-Br-cAMP on the channel in the cell-attached mode. In inside-out patches, PKA catalytic subunit (PKAc)+ATP had no effect on the channel activity, but when channel activity was maintained by CaM+ATP, subsequent addition of PKA significantly increased the channel activity. Meanwhile, phosphorylation with PKA prevents the time-dependent attenuation of the CaM effect. These results indicate that PKA modulation of Ca²⁺ channel requires coordination with CaM. [Jpn J Physiol 54 Suppl:S127 (2004)]