KMUP-1 inhibits L-type Ca²⁺ channels involved the protein kinase C in rat basilar artery myocytes.

This study investigated whether KMUP-1, a xanthine-based derivative, inhibits L-type Ca(2+) currents (I(Ca,L)) in rat basilar artery smooth muscle cells (RBASMCs). We used whole cell patch-clamp recording to monitor Ba(2+) currents (I(Ba)) through L-type Ca(2+) channels (LTCCs). Under voltage-clamp conditions, holding at -40 mV, KMUP-1 (1, 3, 10 μM) inhibited I(Ba) in a concentration-dependent manner and its IC(50) value was 2.27 ± 0.45 μM. A high concentration of KMUP-1 (10 μM) showed without modifying the I(Ba) current-voltage relationship. On the other hand, the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA, 1 μM) increase I(Ba) was inhibited by KMUP-1. Pretreatment with the PKC inhibitor chelerythrine (5 μM) intensified KMUP-1-inhibited I(Ba). However, the Rho kinase inhibitor Y-27632 (30 μM) failed to affect the I(Ba) inhibition by KMUP-1. In light of these results, we suggest that KMUP-1 inhibition of LTCCs in concentration- and voltage-dependent manners in RBASMCs may be due, at least in part, to its modulation of the PKC pathway.