title: Role of calcium and calmodulin in the interaction between islet cell secretion granules and plasma membranes.
abstract: The effects of calcium and calmodulin on the binding of islet secretion granules to plasma membrane vesicles was studied. Free Ca++ (10(-7) to 10(-4) M) produced a concentration-dependent increase in the binding of inside-out. 125I-labeled plasma membrane vesicles to secretion granules; maximum stimulation occurred at 10(-5) M. By contrast, Ca++ had no effect on binding when either inside-out red blood cell or right-side-out islet plasma membrane vesicles were used. Calmodulin (1 microM), in the presence of 10(-4) M Ca++, increased the binding two-fold as compared to Ca++ alone, and trifluoperazine (TFP), and inhibitor of calmodulin, produced a concentration-dependent inhibition of the calmodulin effect. TFP also inhibited the binding produced by 10(-4) M Ca++ in the absence of exogenous calmodulin. These results suggest that Ca++ in the presence of calmodulin modulates the interaction between islet secretion granules and the cytoplasmic surface of the plasma membrane.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002135:Calcium-Binding Proteins / Q000494:pharmacology*; D002147:Calmodulin / Q000494:pharmacology*; D002462:Cell Membrane / Q000378:metabolism; D003594:Cytoplasmic Granules / Q000187:drug effects / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005399:Fishes; D007515:Islets of Langerhans / Q000187:drug effects / Q000648:ultrastructure*; D014268:Trifluoperazine / Q000494:pharmacology
chemical_list: D002135:Calcium-Binding Proteins; D002147:Calmodulin; D014268:Trifluoperazine; D002118:Calcium