Beschreibung:
<jats:p>Endothelin-1 (ET-1) has acute positive inotropic effects, but consequences of chronically increased ET-1 on contractile function of cardiac myocytes are largely unknown. In the present study, effects of long-term treatment with ET-1 (10 nM) for 5 days on both force development [force of contraction (FOC)] and kinetics of contraction were determined in heart tissue reconstituted from rat cardiac cells. Isometric force was measured in response to cumulative concentrations of Ca<jats:sup>2+</jats:sup>and isoprenaline. ET-1 augmented basal FOC by 64 ± 11% ( P < 0.05), which was associated with a significantly blunted contractile response to Ca<jats:sup>2+</jats:sup>and isoprenaline. Moreover, ET-1 significantly prolonged relaxation (62 ± 3 vs. 53 ± 2 ms). Selective ET<jats:sub>A</jats:sub>(BQ-123) and ET<jats:sub>B</jats:sub>receptor blockade (BQ-788) demonstrated that effects of ET-1 on contractile function were mediated through the ET<jats:sub>A</jats:sub>receptor subtype. Effects of ET-1 were prevented by cotreatment with either Ro31-8425, a PKC inhibitor, or dimethylamiloride, an inhibitor of the Na<jats:sup>+</jats:sup>/H<jats:sup>+</jats:sup>exchanger. In contrast to long-term ET-1 treatment, no changes in contractile parameters were observed after ET-1 treatment for 3 h before force measurement. These data suggest that chronic ET-1 stimulation has dual effects on contractility: improvement of basal force but impairment of twitch kinetics and inotropic responsiveness to β-adrenoceptor stimulation. The signaling pathways involved include ET<jats:sub>A</jats:sub>receptors, PKC, and the Na<jats:sup>+</jats:sup>/H<jats:sup>+</jats:sup>exchanger. The present in vitro findings raise the possibility that ET-1 may exert both adaptive and maladaptive effects in the failing myocardium in which local accumulation of ET-1 is present.</jats:p>