Altered inotropic response of endothelin-1 in cardiomyocytes from rats with isoproterenol-induced cardiomyopathy

OBJECTIVE: The positive inotropic effect of endothelin-1 (ET-1) on normal myocardial contraction may be altered in pathological states. The purpose of this study was to assess the direct effect of ET-1 on cardiomyocyte performance and its cellular mechanism in congestive heart failure (CHF). METHODS: We measured the plasma levels of ET-1 and compared the effects of ET-1 (10(-10)-10(-8) M) on contractile performance and the Ca2+i transient in the myocytes of left ventricles (LV) from 15 age-matched normal adult rats and 15 rats with isoproterenol (ISO)-induced CHF. RESULTS: With CHF, the plasma levels of ET-1 (19.7 +/- 6.3 vs. 4.1 +/- 0.5 fmol/ml, p < 0.05) were markedly elevated. In normal myocytes, superfusion of ET-1 caused significant increases in the systolic amplitude (SA, 8-16%) and the peak velocity of shortening (dL/dtmax, 20-35%; p < 0.01) without causing a change in the peak Ca2+i transient. In contrast, in myocytes from CHF rats, ET-1 produced significant reductions in SA (9-13%) and in the velocity of relengthening, dR/dtmax (10-14%; p < 0.05). The myocytes' dR/dtmax also decreased by 8-10% (p < 0.05). These changes were associated with a significant decrease in the peak Ca2+i transient (20-23%, p < 0.01). These responses to ET-1 were abolished by the incubation of myocytes with an ETA receptor antagonist (BQ123) or a protein kinase C (PKC) inhibitor (H-7 or staurosporine). CONCLUSION: ISO-induced CHF is associated with elevated plasma ET-1 and an altered cardiomyocyte response to ET-1. After CHF, ET-1 produces a direct depression of cardiomyocyte contractile performance that is associated with a significant decrease in the peak Ca2+i transient. These effects are likely to be mediated through ETA receptors and involve the PKC pathway.