The effect of HCO3- on anion-stimulated ATPase from rat parotid granules.
ATPase from isolated secretory granules was stimulated in a concentration-dependent manner by HCO3- above 0.9 mM. Maximal stimulation was found at about 16 mM HCO3- and was about half of that with sulphite (SO3(2-)). The activation site(s) appeared to be similar to at least one class of SO3(2-) sites, HCO3(-)-stimulate ATPase was inhibited by SITS. Furthermore, maximal stimulation with SO3(2-) was not enhanced with HCO3-. At low Mg2+ concentrations, Ca2+ stimulated granule ATPase. At higher concentrations of Mg2+ (0.5 mM and above), Ca2+ at 0.1 mM or less had little effect on HCO3(-)-ATPase, and Ca2+ at 4 mM inhibited HCO3(-)-ATPase. At concentrations of Ca2+ above 0.44 mM, the enzyme was partially stimulated in the absence of Mg2+ and presence of HCO3-. Mitochondrial contamination did not account for the presence of ATPase in the isolated granule fraction. The granule ATPase may be regulated by HCO3- and calcium and this could be related to changes in the granule environment during exocytosis.
Dowd
F
F
Department of Pharmacology, Creighton University Medical and Pharmacy Schools, Omaha, NE 68178.
Vasavada
B
B
Nazeri
A
A
Hicks
J
J
Makoid
M
M
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D000838:Anions; D001639:Bicarbonates / Q000494:pharmacology*; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D002118:Calcium / Q000494:pharmacology; D003594:Cytoplasmic Granules / Q000201:enzymology* / Q000648:ultrastructure; D003576:Electron Transport Complex IV / Q000378:metabolism; D008928:Mitochondria / Q000201:enzymology; D010306:Parotid Gland / Q000201:enzymology* / Q000648:ultrastructure; D051381:Rats; D013385:Succinate Dehydrogenase / Q000378:metabolism; D013461:Sulfur Oxides / Q000494:pharmacology
D000838:Anions; D001639:Bicarbonates; D013461:Sulfur Oxides; D013385:Succinate Dehydrogenase; D003576:Electron Transport Complex IV; D000251:Adenosine Triphosphatases; D017301:Ca(2+) Mg(2+)-ATPase; C011118:sulfur trioxide; D002118:Calcium