title: Passive transport of Rb+ by hog gastric (H+,K+)-ATPase.
abstract: 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.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active; D005753:Gastric Mucosa / Q000201:enzymology*; D017506:H(+)-K(+)-Exchanging ATPase; D006859:Hydrogen / Q000378:metabolism; D007700:Kinetics; D009994:Osmolar Concentration; D011188:Potassium / Q000378:metabolism; D012413:Rubidium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D013552:Swine; D014639:Vanadium / Q000494:pharmacology
chemical_list: D014639:Vanadium; D006859:Hydrogen; D000255:Adenosine Triphosphate; D012964:Sodium; D000251:Adenosine Triphosphatases; D017506:H(+)-K(+)-Exchanging ATPase; D012413:Rubidium; D011188:Potassium