INHIBITORY EFFECTS OF OUABAIN ON EARLY HEART DEVELOPMENT AND CARDIOMYOGENESIS IN THE CHICK-EMBRYO

Pericardial cavity formation and epithelialization of the cardiac prec ursor cell population constitute a critical developmental period that precedes stable cardiac cell commitment and differentiation. These eve nts delineate the myocardial and endocardial precursor population in t he embryo. Restriction of Na/K-ATPase (the sodium pump) expression to the pre-cardiomyocyte lateral membranes coincides with these events. N a/K-ATPase has been implicated developmentally in cavitation and in ma intaining membrane potential. Experiments were undertaken to determine if the effects of perturbing sodium pump activity will affect pericar dial cavity formation and, in turn, whether heart formation and/or car diac cell commitment will be affected. We incubated whole chick embryo s in vitro between stages 5 to 8 in the presence of the highly specifi c Na/K-ATPase inhibitor ouabain. Exposure of whole embryos to 10 mu M ouabain (10(-5) M) demonstrated that heart development and precardiomy ocyte differentiation are inhibited principally between stage 5 throug h stage 7. In each stage the degree of inhibition follows a rostrocaud al gradient as development proceeds along the anterior to posterior ax is. After stage 8 ouabain no longer affects heart development or cardi omyogenesis. The inhibition is concentration- and developmental stage- dependent. The inhibition is reversible by elevating the outside potas sium ion concentration [K-o] in the culture medium or by transferring the embryos into normal medium minus ouabain even after 20 hr of ouaba in exposure. The results also suggest that the regulation of the forma tion of the three-dimensional organ is independent from regulation of myogenesis. (C) 1995 Wiley-Liss, Inc.