Inhibition of voltage-gated L-type calcium channels by labedipinedilol-A involves protein kinase C in rat cerebrovascular smooth muscle cells

Labedipinedilol-A, a novel calcium channel blocker with α/β-adrenoceptor blockade properties, inhibits L-type calcium channels (LTCCs) in rat cerebrovascular smooth muscle cells (CSMCs). We used conventional whole cell patch-clamp electrophysiology to investigate Ba2+ currents (IBa) through LTCCs in rat CSMCs enzymatically dissociated from rat cerebral arteries. Labedipinedilol-A (1, 10 µM) reversibly inhibited IBa in a voltage- dependent manner without modifying the IBa current-voltage relationship. The IBa was also abolished by the LTCC blocker nifedipine (1 µM), but enhanced by the LTCC activator Bay K8644 (100 nM). Labedipinedilol-A shifted the steady-state inactivation curve of IBa to more negative potentials. Additionally, labedipinedilol-A had greater inhibitory activity on IBa holding at − 40 mV than at − 80 mV. This might contribute to labedipinedilol-A's more selective effect on vascular muscles compared to cardiac muscles. The protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA) and norepinephrine-enhanced IBa were also inhibited by labedipinedilol-A. Pretreatment with the PKC inhibitor chelerythrine (5 µM) attenuated labedipinedilol-A-mediated IBa inhibition. However, the Rho kinase inhibitor Y-27632 (30 µM) had little effect on labedipinedilol-A inhibition of IBa. Labedipinedilol-A inhibition of voltage-dependent LTCCs may be, at least in part, due to its modulation of the PKC pathway.