ENDOTHELIN ENHANCES DELAYED POTASSIUM CURRENT VIA PHOSPHOLIPASE-C IN GUINEA-PIG VENTRICULAR MYOCYTES

The effects of endothelin, a novel vasoconstrictive peptide, on the delayed rectifier K+ current (I(K)) were examined in single dialyzed cells from guinea pig ventricles. Either big endothelin or endothelin-1 enhanced I(K) at a dissociation constant of 2 nM with L-type Ca2+ current being unaffected. Under intracellular perfusion with pCa 7.6 solution, 3 nM big endothelin increased I(K) by 55 +/- 38.5%. Either pretreatment with 10-mu-M 1-(5-isoquinolinylsulfonyl)-2-methyl-piperazine (H 7) or a low Ca2+ [10 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) and minus CaCl2] internal solution diminished the enhancement. Preceding stimulation of protein kinase C (PKC) by 10-20 nM 12-O-tetradecanoylphorbol-13-acetate also reduced the degree of enhancement. When Na+ was eliminated from the solutions, endothelin increased I(K) distinctively in cells internally dialyzed with a low Ca2+ solution. This enhancement was not abolished by either pretreatment with H 7 or by removal of Ca2+ from the external perfusate but by increasing the internal EGTA concentration to 40 mM. Preincubation with ryanodine or internal perfusion with heparin also reduced the I(K) enhancement under Na+-free conditions. Intracellular application of 200-mu-M guanosine 5'-O-(3-thiotriphosphate) effectively attenuated the effect of endothelin. It is concluded that endothelin enhances I(K) via phospholipase C-mediated PKC activation and intracellular Ca2+ mobilization. GTP-binding protein is involved in these reactions.