The protein kinase inhibitor, staurosporine, inhibits L-type Ca2+ current in rabbit atrial myocytes

A whole-cell patch recording was used to determine the effects of staurosporine (ST), a potent protein kinase C (PKC) inhibitor, on L-type Ca2+ channel (LTCC) activity in rabbit atrial myocytes. Bath application of ST (300 nM) caused a significant reduction in peak I-V relationship of LTCC (from −16.8 ± 2.55 to −3.74 ± 1.22 pA pF−1 at 0 mV). The level of L-type Ca2+ current (ICa,L) inhibition produced by ST was independent of the voltage at which the effect was measured. ST inhibited the ICa,L in a dose-dependent manner with a Kd value of 61.98 ± 6.802 nM. ST shifted the activation curve to more positive potentials, but did not have any significant effect on the voltage dependence of the inactivation curve. Other PKC inhibitors, GF 109203X (1 μM) and chelerythrine (3 μM), and PKA inhibitor, PKA-IP (5 μM), did not show any inhibitory effect on ICa,L. Additional application of ST in the presence of isoproterenol (1 μM), a selective β-adrenoreceptor agonist, reduced peak ICa,L (78.2%) approximately to the same level with single application of ST (77.8%). In conclusion, our results indicate that ST directly blocks the LTCC in a PKC or PKA-independent manner on LTCC and it should be taken into consideration when ST is used in functional studies of ion channel modulation by protein phosphorylation.