Effects of endothelin-1 on Ca2+ signaling in guinea-pig ventricular myocytes: Role of protein kinase C

The effects of ET-1 on contraction. Ca2+ transient and L-type Ca2+ current (I-Ca.L) were studied in single cells isolated From ventricles of guinea-pi g hearts. The aim of our study was to elucidate the mechanism of the positi ve inotropic effect during endothelin receptor stimulation by focusing on t he role of PKC. ET-1 at concentrations of 5 and 10 nM produced a biphasic p attern of inotropism: a first decrease in contraction by 34.4 +/- 2.5% of t he control followed by a sustained increase in contraction by 66.6 +/- 8.4% , (mean +/- SEM, n = 9), The Ca2+ transient decreased by 13.5 +/- 1.0%, dur ing the negative inotropic phase, while it increased by 58.1 +/- 8.4%; (n = 10) during the positive inotropic phase. Using the whole-cell voltage-clam p technique with conventional microelectrodes, the application of ET-I (5 n M) increased the I-Ca.L by 32.6 +/- 5.1% (n = 10), which was preceded by a short-lived decrease in I-Ca.L. Incubation of myocytes with pertussis toxin (PTX, at 2 mu g/ml for >3 h at 35 degrees C) failed to block the ET-l-indu ced enhancement of I-Ca.L. The increases in contraction, Ca2+ transient, an d I-Ca.L by ET-1 were inhibited by pretreatment with 5-N-methyl-N-isobutyl amiloride (MIA: 10 mu M), an amiloride analog, and a novel selective Na+/H exchange inhibitor HOE694 (10 mu M). To determine whether activation of pr otein kinase C (PKC) is responsible for the enhancement of I-Ca.L by ET-1, we tested a PKC inhibitor, GF109203X, and found that it does exert an inhib itory effect oil the ET-1-induced I-Ca.L increase. Our study suggests that during ET receptor stimulation an increase in I-Ca.L due to stimulation of Na+/H+ exchange via PKC activation causes an increase in Ca2+ transients an d thereby in the contractile force of the ventricular myocytes. (C) 1999 Ac ademic Press.