DUAL ACTION OF ENDOTHELIN-1 ON THE CA-2+-ACTIVATED K+ CHANNEL IN SMOOTH-MUSCLE CELLS OF PORCINE CORONARY-ARTERY

The effects of endothelin-1 (ET-1) on the activity of the large Ca2+-activated K+ channel (BK channel) in enzymatically dissociated smooth muscle cells of porcine coronary artery were studied with the cell-attached patch-clamp technique. ET-1 at concentrations between 0.1 and 10 nM potentiated the BK channel activity. This effect was maximal at 1 nM ET-1, resulting in an average of 4.2-fold increase in channel open-state probability as compared with control. ET-1 at concentrations higher than 10 nM produced an irreversible inhibition of the BK channel activity, primarily due to a marked decrease in the channel mean open-time. The activation by lower doses of ET-1, but not the inhibition by higher doses of ET-1, of the BK channel was blocked by 0.1-mu-M PN 200-110, a Ca2+ channel blocker. The modulation of the BK channel activity in smooth muscle cell membrane may be a possible mechanism for ET-induced vasodilator and vasoconstrictor actions.