Abstract
We tested the hypothesis that atrial natriuretic peptide (ANP) has a direct negative inotropic effect on the cultured chick embryo ventricular cell, an experimental system devoid of endogenous neurotransmitters. At 10(-8) and 2.5 x 10(-7) mol/l ANP [rat ANP-(1-23)] significantly and reversibly decreased contractility in spontaneously beating cells. The positive inotropic effect of angiotensin II (2.5 X 10(-7) mol/l) on spontaneously beating cells was fully antagonized by ANP (2.5 X 10(-7) mol/l) and the amplitude of contraction decreased below control levels. In contrast (1) the increase in contractility in response to extracellular calcium was significantly less altered by ANP and (2) the time-course of the positive inotropic effect of the calcium-channel agonist Bay-K-8644 (5 x 10(9) mol/l) or of the beta-adrenergic agonist isoproterenol (10(-6) mol/l) was unchanged by ANP. These results indicate that ANP-(1-23) has a direct negative inotropic effect on cultured chick heart cells and may affect intracellular messengers involved in the cardiac effects of angiotensin II.
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