Endothelin enhances delayed potassium current via phospholipase C in guinea pig ventricular myocytes

Abstract

The effects of endothelin, a novel vasoconstrictive peptide, on the delayed rectifier K+ current (IK) were examined in single dialyzed cells from guinea pig ventricles. Either big endothelin or endothelin-1 enhanced IK 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 IK by 55 +/- 38.5%. Either pretreatment with 10 microM 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 IK 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 IK enhancement under Na(+)-free conditions. Intracellular application of 200 microM guanosine 5'-O-(3-thiotriphosphate) effectively attenuated the effect of endothelin. It is concluded that endothelin enhances IK via phospholipase C-mediated PKC activation and intracellular Ca2+ mobilization. GTP-binding protein is involved in these reactions.

KCNE1 enhances phosphatidylinositol 4,5-bisphosphate (PIP 2 ) sensitivity of I Ks to modulate channel activity

“…The generation of second messengers in addition to the effective decrease of PIP 2 levels makes I Ks regulation by PLC activation complex as I Ks is known to be sensitive to PKC phosphorylation (24), intracellular calcium (25), and PIP 2 (6). This complex regulation in response to activation of Gqα may be reflected in the biphasic response of heterologously expressed I Ks channels (26) and the conflicting reports of effects on endogenous I Ks in myocytes (27)(28)(29). Our current results show that the PIP 2 sensitivity of the I Ks channel is dependent on the KCNE1 expression level relative to that of KCNQ1 (Fig.…”

Augmentation of the Delayed Rectifier Potassium Current by ETA Endothelin Receptor in Guinea Pig Atrial Myocytes

“…The concentration of intracellular Ca 2+ was kept low with 5 mM EGTA in the pipette in the present study, which may suggest involvement of the calcium-insensitive type of PKC (14) as reported for the modulation of the ATP-sensitive potassium channel (15). However, the present data does not exclude a possible involvement of the calcium-sensitive isoform of PKC, since stronger buffering of intracellular Ca 2+ with 40 mM EGTA has been reported to abolish the ET-1-induced augmentation of I K in guinea pig ventricular myocytes (5). Identification of the responsible PKC isoform awaits further study.…”

Regulation of Cardiac IKs Potassium Current by Membrane Phosphatidylinositol 4,5-Bisphosphate

“…However, it was previously demonstrated in guinea pig ventricular myocytes that endothelin enhances I Ks via PLC-mediated PKC activation and intracellular Ca 2ϩ mobilization (44). It was also shown that ␣ 1 -adrenceptor-induced potentiation of I Ks is mediated through PKC activation in the same cell types (45).…”

“…These observations appear to be apparently in contrast with the present results. To date, there has been little convincing evidence supporting the view that the I Ks channel is inhibited by the receptor-mediated activation of PLC in native cardiac myocytes (44). It may be probable that the native and recombinant ion channels behave differently to various exper- imental stimuli.…”