ACTIVATION OF BKCA CHANNEL VIA ENDOTHELIN-ETA RECEPTORS IN PORCINE CORONARY-ARTERY SMOOTH-MUSCLE CELLS

It has been demonstrated previously that endothelin-l stimulates the C a2+-activated K+ (BKCa) channel activity in porcine coronary artery sm ooth muscle cells. The purpose of the present study was to delineate t he endothelin receptor subtype involved in this action. In receptor bi nding studies, [I-125]endothelin-l was shown to bind to the homogenate of porcine primary coronary artery smooth muscle cells in a single cl ass 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 dis placed the binding of [I-125]endothelin-1 to these cells with respecti ve IC50 values of 70 and 17 000 pM, a 240-fold difference in potency. The effects of endothelin-3 on the activity of the BKCa channel in por cine coronary artery smooth muscle cells were examined using the cell- attached patch-clamp technique. Similar to endothelin-l. endothelin-3 also exhibited a bell-shaped concentration-response curve. A maximal i ncrease 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-l was about 100-fold more potent and 3. 4-fold more efficacious than endothelin-3 in this action. Both the rec eptor binding and the electrophysiological results suggest that the ef fects of endothelins on the BKCa channel are mediated through the endo thelin ETA receptor subtype. (C) 1997 Elsevier Science B.V.