[Atrial natriuretic factor diminishes the contractility of the cardiac cell in culture].

The hypotensive effect of ANP has been associated with lowered cardiac output. Although only minor or no negative inotropic effect was found in vitro, a direct myocardial depressant effect of ANP remains a possible mechanism in vitro, in addition to the reduction in cardiac preload. Therefore we tested the hypothesis of a direct negative inotropic effect of ANP on the cultured chick embryo ventricular cell, an experimental system which contains no neural elements and no endogenous neurotransmitters. ANP (rat-ANP 1-23) 10(-8) M significantly and reversibly decreased contractility in spontaneously beating cells. A further decrease (-30 +/- 4 p. 100 of initial amplitude of contraction) was observed at 2.5 x 10(-7) M: -17 +/- 4 p. 100 of initial amplitude). The positive inotropic effect of angiotensin II (2.5 x 10(-7) M) on spontaneously beating cells was fully antagonized by ANP (2.5 x 10(-7) M) and amplitude of contraction decreased under control levels. By contrast (1) the increase in contractility in response to extra-cellular calcium (increased from 1.5 to 2.1 mM) 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) M) or the beta-adrenergic agonist isoproterenol (10(-6) M) was unchanged by ANP. These results indicate a direct negative inotropic effect of ANP (1-23) on cultured chick heart cells and suggest an effect on intracellular messengers involved in the cardiac effects of angiotensin II.(ABSTRACT TRUNCATED AT 250 WORDS)