title: Stimulation of monovalent cation active transport by low concentrations of cardiac glycosides. Role of catecholamines.
abstract: The stimulatory effect of low concentrations of ouabain on the Na-K pump in isolated guinea pig left atria was studied in vitro by assessing active transport of the K(+) analog Rb(+). Active transport of Rb(+) was stimulated 20+/-8% (SEM, P < 0.05) above control values by 3 nM ouabain, but was inhibited by concentrations >10 nM. Preincubation with the beta-adrenergic antagonist propranolol (1 muM) completely blocked stimulation of active transport of Rb(+) by 3 nM ouabain. Norepinephrine, 10 nM, increased Rb(+) active transport 29+/-10% (P < 0.02) above control values. The beta-adrenergic agonist l-isoproterenol, 10 nM, increased active transport of Rb(+) by 33+/-10% (P < 0.01) above control levels. This stimulatory effect was abolished if tissues were first exposed to propranolol. Tyramine (0.1 muM), a stimulator of endogenous catecholamine release, increased active transport of Rb(+) 26+/-12% (P < 0.05) above control values. Rb(+) active transport was not significantly changed when left atrial tissues were incubated with alpha-adrenergic agonists or antagonists. Ouabain stimulation of Rb(+) active transport was prevented by in vivo depletion of myocardial endogenous catecholamines by either reserpine or 6-hydroxydopamine. These findings indicated that in myocardial tissue, Na-K pump stimulation by low concentrations of ouabain is mediated at least in part through beta-adrenergic effects of endogenous catecholamines.
mesh_terms: D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002395:Catecholamines / Q000378:metabolism*; D006168:Guinea Pigs; D006325:Heart Atria / Q000378:metabolism; D006352:Heart Ventricles / Q000378:metabolism; D007545:Isoproterenol / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology*; D010042:Ouabain / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism*; D011433:Propranolol / Q000494:pharmacology*; D012413:Rubidium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*
chemical_list: D002395:Catecholamines; D010042:Ouabain; D012964:Sodium; D011433:Propranolol; D007545:Isoproterenol; D012413:Rubidium; D011188:Potassium; D009638:Norepinephrine