Activation of the Na(+)-K+ pump in frog erythrocytes by catecholamines and phosphodiesterase blockers.
K+ and Na+ influx into frog erythrocytes incubated in standard saline was studied using 86Rb and 22Na as tracers. 10 microM isoproterenol (ISP) produced a significant increase in K+ influx for the first 15 min, which was sustained during the entire 60 min of cell incubation. Treatment of red cells with the phosphodiesterase (PDE) blockers theophylline (THEO, 1 and 5 mM) or 3-isobutyl-1-methylxanthine (IBMX, 0.5 mM) was also accompanied by an enhancement in K+ influx. A distinct additive effect on K+ influx into red cells was found when ISP and THEO or IBMX were added together. The increase in K+ transport induced by ISP plus IBMX was totally abolished by pretreatment of red cells with 0.1 mM ouabain. The ouabain-sensitive K+ influx in frog erythrocytes was elevated in the presence of ISP plus IBMX to 2.05 +/- 0.45, as compared with the control level of 0.39 +/- 0.11 mmol/L cells/hr (P < 0.001). Similar effects of ISP and IBMX on K+ influx were observed after chloride was replaced by nitrate. A dose-related increase in K+ influx into frog erythrocytes was observed at ISP concentrations of 10(-8)-10(-6) M, with a half-maximal stimulatory concentration of approximately 0.02 microM. The effects of ISP (10(-8)-10(-5) M) on K+ transport were completely abolished with 10 microM of the beta-adrenergic blocker propranolol, but alpha-adrenergic antagonists (phentolamine, prazosin, and yohimbine) did not alter the ISP-induced increase in K+ influx. The drugs tested had no effect on 22Na influx in frog red cells, but ISP produced a small decline (13%) in intracellular Na+ concentration. Thus, our study indicates that catecholamines and PDE blockers enhance K+ (86Rb) transport in frog erythrocytes mediated by Na(+)-K+ pump activity. The frog erythrocyte membrane may serve as a convenient model to investigate the hormonal modulation of the Na(+)-K+.
Gusev
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GP
Sechenov Institute of Evolutionary Physiology and Biochemistry, St-Petersburg, Russia. ion@ief.spb.su
Agalakova
N I
NI
Lapin
A V
AV
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D018674:Adrenergic Antagonists / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D004912:Erythrocytes / Q000187:drug effects* / Q000201:enzymology* / Q000378:metabolism; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D009638:Norepinephrine / Q000494:pharmacology*; D010042:Ouabain / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology*; D011188:Potassium / Q000097:blood; D011433:Propranolol / Q000494:pharmacology; D011896:Rana temporaria; D012964:Sodium / Q000097:blood; D000254:Sodium-Potassium-Exchanging ATPase / Q000097:blood*; D013806:Theophylline / Q000494:pharmacology
D018674:Adrenergic Antagonists; D010726:Phosphodiesterase Inhibitors; D010042:Ouabain; D012964:Sodium; D011433:Propranolol; D013806:Theophylline; D000254:Sodium-Potassium-Exchanging ATPase; D007545:Isoproterenol; D011188:Potassium; D015056:1-Methyl-3-isobutylxanthine; D009638:Norepinephrine; D010646:Phentolamine