Abstract
AIM: To investigate the mechanisms underlying the activation of ATP-sensitive potassium channels (K(ATP)) by iptakalim in cultured rat mesenteric microvascular endothelial cells (MVECs). METHODS: Whole-cell KATP currents were recorded in MVECs using automated patch clamp devices. Nucleotides (ATP, ADP and UDP) were added to the internal perfusion system, whereas other drugs were added to the cell suspension on NPC-1 borosilicate glass chips. RESULTS: Application of iptakalim (10 and 100 μmol/L) significantly increased the whole-cell K(ATP) currents, which were prevented by the specific K(ATP) blocker glibenclamide (1.0 μmol/L). The opening of K(ATP) channels by iptakalim depended upon the intracellular concentrations of ATP or NDPs: iptakalim activated K(ATP) channels when the intracellular ATP or NDPs were at 100 or 1000 μmol/L, and was ineffective when the non-hydrolysable ATP analogue ATPγS (1000 μmol/L) was infused into the cells. In contrast, the K(ATP) opener pinacidil activated K(ATP) channels when the intracellular concentrations of ATP or NDPs ranged from 10 to 5000 μmol/L, and even ATPγS (1000 μmol/L) was infused into the cells. CONCLUSION: Iptakalim activates K(ATP) channels in the endothelial cells of resistance blood vessels with a low metabolic status, and this activation is dependent on both ATP hydrolysis and ATP ligands.