Effects of ouabain, hypothermia and anoxia on cation fluxes in embryonic chick heart

¹ Department of Pharmacology, University of Mississippi Medical Center, Jackson, Mississippi

An active cation transport mechanism is believed to exist in embryonic chick myocardium by at least 2 days incubation. Classical effects of ouabain on unidirectional Na and K movements and contents are demonstrated in isolated ventricles of the developing embryo and hatched chick. In addition to inhibiting active Na extrusion and K entry, a marked stimulation of a passive Na in-K out exchange mechanism is indicated. Ouabain's actions on Na and K movements are believed to be primarily toxic manifestations. Hypothermia inhibits K influx and efflux equally between 30° and 20°C. Not until temperatures of 10° and 5°C are reached do Q₁₀'s for influx become greater than for efflux. Effects of anoxia on cation movements in young embryos are small, but increase greatly at older ages. Active transport of Na and K is sensitive to ouabain and relatively insensitive to hypothermia at all ages tested. It is relatively insensitive to anoxia at early ages. Changes in ventricular cation content are given for all conditions.