Passive transport of Rb+ by hog gastric (H+,K+)-ATPase

• Published in: The Journal of biological chemistry Vol. 259; no. 19; pp. 11861 - 11867
• Main Authors: SOUMARMON, A, RANGACHARI, P. K, LEWIN, M. J. M
• Format: Journal Article
• Language: English
• Published: Bethesda, MD American Society for Biochemistry and Molecular Biology 10.10.1984
• Subjects: Adenosine Triphosphatases - metabolism; Adenosine Triphosphate - pharmacology; Animals; Biological and medical sciences; Biological Transport, Active; Cell physiology; Fundamental and applied biological sciences. Psychology; Gastric Mucosa - enzymology; H(+)-K(+)-Exchanging ATPase; Hydrogen - metabolism; Kinetics; Membrane and intracellular transports; Molecular and cellular biology; Osmolar Concentration; Potassium - metabolism; Rubidium - metabolism; Sodium - metabolism; Swine; Vanadium - pharmacology; Vesicle; Stomach; Vertebrata; Mammalia; Membrane transport; ATPase; Membrane; Artiodactyla; Microsome; Rubidium; Ungulata; Pig
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(20)71291-3

Gastric vesicles enriched in (H+,K+)-ATPase were prepared from hog fundic mucosa and studied for their ability to transport K+ using 86Rb+ as tracer. In the absence of ATP, the vesicles elicited a rapid uptake of 86Rb+ (t 1/2 = 45 +/- 9 s at 30 degrees C) which accounted for both transport and binding. Transport was osmotically sensitive and was the fastest phase. It was not limited by anion permeability (C1- was equivalent to SO2-4) but rather by availability of either H+ or K+ as intravesicular countercation suggesting a Rb+-K+ or a Rb+-H+ exchange. Selectivity was K+ greater than Rb+ greater than Cs+ much greater than Na+,Li+. The capacity of vesicles which catalyzed the fast transport of K+ was 83 +/- 4% of maximal vesicular capacity of the fraction. Addition of ATP decreased both rate and extent of 86Rb+ uptake (by 62 and 43%, respectively with 1 mM ATP) with an apparent Ki of 30 microM. Such an effect was not seen on 22Na+ transport. ATP inhibition of transport did not require the presence of Mg2+, and inhibition was also produced by ADP even in the presence of myokinase inhibitor. On the other hand, 86Rb+ uptake was as strongly inhibited by 200 microM vanadate in the presence of Mg2+. Efflux studies suggested that ATP inhibition was originally due to a decrease of vesicular influx with little or no modification of efflux. Since ATP, ADP, and vanadate are known modulators of the (H+,K+)-ATPase, we propose that, in the absence of ATP, (H+,K+)-ATPase passively exchanges K+ for K+ or H+ and that ATP, ADP, and vanadate regulate this exchange.