Endothelin stimulates multiple responses in isolated adult ventricular cardiac myocytes

We have examined the responses to endothelin (ET) in isolated adult cardiac myocytes from both rodent and feline species to assess whether endothelin may have a role in the induction or mediation of cardiac hypertrophy in the adult animal. We have evidence that ET acts by more than one mechanism to promote cell-signaling events believed important in growth regulation. In isolated adult cardiac ventricular myocytes labeled overnight with [³H]inositol, endothelin (ET) promoted a two- to fourfold increase in the accumulation of inositol polyphosphates in a dose-dependent manner with an half-maximal effective concentration (EC₅₀) of ~5 nM. In contrast, picomolar concentrations of ET promoted an increase in both the extent and velocity of sarcomere shortening in electrically stimulated myocytes. Pretreatment of cells with pertussis toxin had no effect on the ET-stimulated phosphoinositide hydrolysis, but blocked the ET-stimulated positive inotropic effect. In addition to these early responses to ET, results obtained by Northern blot analysis demonstrate that exposure of isolated cardiac myocytes to 100 nM ET promoted the expression of c-fos and c-zif in both mammalian species. These data demonstrate that ET stimulates multiple cell-signaling pathways in adult mammalian cardiac myocytes. A paracrine mechanism of regulation of adult myocardium is suggested.