Abstract
Rat reticulocytes were used to prepare endocytic vesicles to study calcium fluxes across the endosomal membrane. We used 45Ca2+, and found that endocytic vesicles from reticulocytes present a Ca(2+)-ATPase that pumps Ca2+ into the lumen of vesicles. This activity was sensitive to vanadate and the calmodulin antagonists: trifluoperazine and calmidazolium. Western blot analysis using a monoclonal antibody evidenced that Ca(2+)-ATPase present in reticulocyte endocytic vesicles is probably the same as the erythrocyte Ca2+ pump. Ca2+ pump activity was shown to be partially inhibited by GTP gamma S. Moreover, mastoparan and benzalkonium chloride, both activators of heterotrimeric G proteins, were found to decrease 45Ca2+ uptake by endocytic vesicles. These results suggest the involvement of a trimeric G protein in the modulation of Ca(2+)-ATPase.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Animals
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Benzalkonium Compounds / pharmacology
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Blotting, Western
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Calcium / antagonists & inhibitors
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Calcium / pharmacokinetics
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Calcium-Transporting ATPases / antagonists & inhibitors
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Calcium-Transporting ATPases / drug effects
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Calcium-Transporting ATPases / metabolism*
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Calmodulin / antagonists & inhibitors
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Calmodulin / pharmacology
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Cell Membrane / drug effects
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Cell Membrane / metabolism
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Dose-Response Relationship, Drug
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Electrophoresis, Polyacrylamide Gel
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Endocytosis / drug effects
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Endocytosis / physiology*
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Endosomes / drug effects
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Endosomes / metabolism*
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Enzyme Inhibitors / pharmacology
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Erythrocytes / drug effects
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Erythrocytes / metabolism
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GTP-Binding Proteins / drug effects
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GTP-Binding Proteins / metabolism*
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Guanosine 5'-O-(3-Thiotriphosphate) / pharmacology
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Imidazoles / pharmacology
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Intercellular Signaling Peptides and Proteins
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Peptides
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Rats
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Rats, Sprague-Dawley
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Reticulocytes / drug effects
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Reticulocytes / metabolism*
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Trifluoperazine / pharmacology
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Vanadates / pharmacology
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Wasp Venoms / pharmacology
Substances
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Benzalkonium Compounds
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Calmodulin
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Enzyme Inhibitors
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Imidazoles
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Intercellular Signaling Peptides and Proteins
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Peptides
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Wasp Venoms
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Trifluoperazine
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Guanosine 5'-O-(3-Thiotriphosphate)
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Vanadates
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calmidazolium
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mastoparan
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GTP-Binding Proteins
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Calcium-Transporting ATPases
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Calcium