High Na content of early embryonic chick heart

¹ Department of Pharmacology, University of Mississippi School of Medicine, Jackson, Mississippi

Ultrafiltration and fractional centrifugation methods using Na²⁴- and K⁴²-labeled myocardia were employed to demonstrate the fractions of bound and free Na and K in isolated embryonic chick ventricles between 2 and 19 days of development. The data revealed a high percentage of bound Na in the cell-solids fraction of 2- and 3-day hearts. After 5 days Na binding remained constant at 25–30% in the whole homogenate. Bound K remained constant at 25–30% throughout development agreeing with the 70% exchangeability calculated from earlier unidirectional flux experiments. The data confirmed a high degree of Na binding in the early embryonic myocardium and indicated that the large fraction of nonexchangeable ventricular Na at 7 days, measured by flux studies, might depend at least in part on the structural integrity of the myocardial cell rather than on specific binding. Polysaccharide analyses were performed on early embryonic hearts which contained relatively large amounts of cardiac jelly substance. The 2-day heart contains 2–3% acid and 6% neutral polysaccharide. The mucoprotein cardiac jelly is discussed in terms of its Na binding and occluding capacity from the viewpoint of the physicochemical properties of macromolecular systems.