Relative lack of ATP-driven H+ translocase activity in isolated parotid secretory granules.
The possible presence of ATP-driven H+ translocase activity in isolated rat parotid secretory granules has been examined by several approaches. First the transmembrane pH difference measured by either [14C] methylamine or [3H]acetate distribution is not substantially affected by ATP in the presence of membrane-permeating anions. Second, despite a low intrinsic H+ permeability of parotid granule membranes, only a small variably detectable inside-positive transmembrane potential is observed (by altered distribution of radioactive ions) when ATP is added in the absence of permeant anions. Third, ATP-induced lysis of parotid granules is minor and appears to be independent of ATP hydrolysis. Finally, ATP-hydrolase activity of the parotid granule fraction is not stimulated by an H+ ionophore, nor is it susceptible to inhibition by 7-chloro-4-nitrobenz-2-oxa-1,3-diazole at a concentration which decreases the measured ATPase of purified chromaffin granule membranes by more than 80%. These findings suggest that this exocrine secretory granule type, which is characterized by storage of a heterogeneous mixture of secretory proteins, exhibits H+ pump activity which is at most a small fraction of that observed in biogenic amine storage granules of neural and endocrine tissues.
Arvan
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Rudnick
G
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Castle
J D
JD
D000085:Acetates / Q000378:metabolism; D019342:Acetic Acid; D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D002463:Cell Membrane Permeability; D003594:Cytoplasmic Granules / Q000201:enzymology*; D005033:Ethylmaleimide / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D008564:Membrane Potentials; D008744:Methylamines / Q000378:metabolism; D010306:Parotid Gland / Q000648:ultrastructure*; D006180:Proton-Translocating ATPases / Q000378:metabolism*; D051381:Rats; D012966:Sodium Cyanide / Q000494:pharmacology
D000085:Acetates; D008744:Methylamines; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D000255:Adenosine Triphosphate; C027451:methylamine; D006180:Proton-Translocating ATPases; D005033:Ethylmaleimide; D012966:Sodium Cyanide; D019342:Acetic Acid