Further studies of hormone-sensitive sodium and potassium transport in red cells from developing chick embryos.

Abstract

Sodium and potassium transport in the definitive series of chick embryo red cells changes significantly, both qualitatively and quantitatively, during maturation. Sodium efflux and potassium influx consist of three parts: a ouabain-sensitive, a furosemide-sensitive, and a ouabain-furosemide-insensitive component. In chick red cells of most ages, the ouabain-sensitive and furosemide-sensitive parts of the cation fluxes do not overlap. Cation transport in the more mature red cells is increased significantly by epinephrine, whereas cation transport in red cells from younger embryos is stimulated much less. This is a beta-adrenergic effect of epinephrine and is mediated by cyclic AMP. The relative lack of response in younger embryos is not due to the absence of beta-adrenergic receptor or the lack of production of cyclic AMP. Ouabain has no effect on the hormone-sensitive sodium or potassium transport. On the other hand, furosemide nearly completely abolishes the effect of epinephrine. In addition, there is a good correlation between furosemide-sensitive components of both sodium and potassium transport and the epinephrine-sensitive component. Furosemide has no effect on cyclic AMP levels in the presence or absence of epinephrine. This suggests that furosemide may act directly on the cation transport system. In the red cells from younger embryos, furosemide-sensitive units are present but cannot be fully activated by epinephrine. Therefore, the lack of the hormone effect on cation movements in these cells is consistent with the view that the appropriate units are present, but do not respond fully to intracellular cyclic AMP levels.