Restoration of uridine 5′-triphosphate-suppressed delayed rectifying K+ currents by an NO activator KMUP-1 involves RhoA/Rho kinase signaling in pulmonary artery smooth muscle cells

We have demonstrated that KMUP-1 (7-[2-[4-(2-chlorobenzene)piperazinyl]ethyl]-1,3-dimethylxanthine) blunts monocrotaline-induced pulmonary arterial hypertension by altering Ca2+ sensitivity, K+-channel function, endothelial nitric oxide synthase activity, and RhoA/Rho kinase (ROCK) expression. This study further investigated whether KMUP-1 impedes uridine 5′-triphosphate (UTP)-inhibited delayed rectifying K+ (KDR) current in rat pulmonary arteries involved the RhoA/ROCK signaling. Pulmonary artery smooth muscle cells (PASMCs) were enzymatically dissociated from rat pulmonary arteries. KMUP-1 (30μM) attenuated UTP (30μM)-mediated membrane depolarization and abolished UTP-enhanced cytosolic Ca2+ concentration. Whole-cell patch-clamp electrophysiology was used to monitor KDR currents. A voltage-dependent KDR current was isolated and shown to consist of a 4-aminopyridine (5mM)-sensitive component and an insensitive component. The 4-aminopyridine sensitive KDR current was suppressed by UTP (30μM). The ROCK inhibitor Y27632 (30μM) abolished the ability of UTP to inhibit the KDR current. Like Y27632, KMUP-1 (30μM) similarly abolished UTP-inhibited KDR currents. Superfused protein kinase A and protein kinase G inhibitors (KT5720, 300nM and KT5823, 300nM) did not affect UTP-inhibited KDR currents, but the currents were restored by adding KMUP-1 (30μM) to the superfusate. KMUP-1 reversal of KDR current inhibition by UTP predominantly involves the ROCK inhibition. The results indicate that the RhoA/ROCK signaling pathway plays a key role in eliciting PASMCs depolarization caused by UTP, which would result in pulmonary artery constriction. KMUP-1 blocks UTP-mediated PASMCs depolarization, suggesting that it would prevent abnormal pulmonary vasoconstriction.