The role of HCO3-stimulated ATPase in buffer transport.
An ATPase stimulated by HCO-3ions and other oxybases and inhibited by SCN- has been found in main excretory duct of rat submaxillary gland, a tissue, capable of actively secreting HCO-3ions. No such ATPase was found in the rabbit duct, which normally does not secrete HCO-3. The HCO-3ATPase was localized in the plasma membrane fraction of the homogenate, as evidenced by the marker 5'nucleotidase. The activities of the HCO-3ATPase increased in metabolic alkalosis and decreased in metabolic acidosis in parallel to secretion of HCO-3 and K+ ions by the rat salivary duct epithelium. In renal cortex tissue, where HCO-3 is actively reabsorbed respectively H+ is secreted, there was also found a parallel change in the activity of the HCO-3ATPase and the rate of active H+ secretion. These findings provide further evidence that the membrane-bound HCO-3ATPase is involved in active H+/HCO-3 transport. The HCO-3ATPase is not only stimulated by HCO-3 but also by other non transportable oxybases, a finding which indicates H+ rather than HCO-3 being the actively transported component of the buffer system. Small concentrations of K+ ions decrease the Km for HCO-3 and thus yield stimulation of the HCO-3-ATPase. Thport changing in parallel with that of H+/HCO-3 may be taken as indicative for a coupled K+-H+-exchange mechanism to which the HCO-3ATPase is linked.
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology*; D001692:Biological Transport; D002021:Buffers; D004789:Enzyme Activation; D006863:Hydrogen-Ion Concentration; D007668:Kidney / Q000201:enzymology*; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D009928:Organ Specificity; D010179:Pancreas / Q000201:enzymology; D011188:Potassium / Q000494:pharmacology; D011817:Rabbits; D051381:Rats; D012469:Salivary Glands / Q000201:enzymology*; D012964:Sodium / Q000494:pharmacology
D001639:Bicarbonates; D002021:Buffers; D012964:Sodium; D000251:Adenosine Triphosphatases; D008274:Magnesium; D011188:Potassium