Activation of large-conductance Ca2+-activated K+ channels by pinacidil inhuman umbilical vascular endothelial cells

The effect of pinacidil, an opener of ATP-sensitive K+ (K-ATP) channels, on large-conductance Ca2+-activated K+ (BKCa) channels was investigated in cu ltured endothelial cells of human umbilical veins. In whole cell configurat ion, pinacidil (30 mu M) increased the amplitude of K+ outward currents (I- K). Charybdotoxin (100 nM), but not glibenclamide (10 mu M), suppressed pin acidil-induced increase in I-K Neither carbonyl cyanide m-chlorophenyl hydr azone (CCCP; 10 mu M), an inhibitor of mitochondrial Ca2+-uniporter, nor cy closporin A (200 nM), an inhibitor of the mitochondrial permeability transi tion pore, affected pinacidil-induced increase in I-K. In inside-out patch configuration, bath application of pinacidil (30 mu M) did not change singl e channel conductance but increased the activity of BKCa channels. Pinacidi l (30 mu M) shifted the activation curve of BKCa channels to less positive membrane potential by approximately 15 mV. Pinacidil stimulated the activit y of these channels in a concentration-dependent manner. The EC50 value for pinacidil-induced channel activity was 20 mu M. After BKCa channels had be en enhanced by Evans blue (100 mu M), subsequent application of pinacidil ( 100 mu M) did not further increase the channel activity. These results clea rly indicate that in addition to the activation of K-ATP channels, pinacidi l can also stimulate BKCa channels in endothelial cells. These effects coul d contribute to the regulation of vascular tone if similar results were fou nd in endothelial cells in vivo. Drug Dev. Res. 48:6-16, 1999. (C) 1999 Wil ey-Liss, Inc.