Activation of BK Ca channel via endothelin ET A receptors in porcine coronary artery smooth muscle cells

Abstract

It has been demonstrated previously that endothelin-1 stimulates the Ca 2+-activated K + (BK Ca) channel activity in porcine coronary artery smooth muscle cells. The purpose of the present study was to delineate the endothelin receptor subtype involved in this action. In receptor binding studies, [ 125I]endothelin-1 was shown to bind to the homogenate of porcine primary coronary artery smooth muscle cells in a single class of binding sites with K D and B max values of 73 pM and 99 fmol/mg protein, respectively. Furthermore, endothelin-1 and endothelin-3 displaced the binding of [ 125I]endothelin-1 to these cells with respective IC 50 values of 70 and 17 000 pM, a 240-fold difference in potency. The effects of endothelin-3 on the activity of the BK Ca channel in porcine coronary artery smooth muscle cells were examined using the cell-attached patch-clamp technique. Similar to endothelin-1, endothelin-3 also exhibited a bell-shaped concentration-response curve. A maximal increase of 95% in channel open-state probability ( P o) was induced by 100 nM endothelin-3 as compared with the 320% increase in P o by 1 nM endothelin-1. Thus, endothelin-1 was about 100-fold more potent and 3.4-fold more efficacious than endothelin-3 in this action. Both the receptor binding and the electrophysiological results suggest that the effects of endothelins on the BK Ca channel are mediated through the endothelin ET A receptor subtype. © 1997 Elsevier Science B.V. All rights reserved.