Secretory responses of rat peritoneal mast cells to high intracellular calcium.
The patch-clamp technique was used to investigate the secretory responses of rat peritoneal mast cells at various intracellular calcium concentrations ([Ca2+]i). When Calcium was introduced into the cell with pipette-loaded dibromo-BAPTA, elevation of [Ca2+]i into the range 1-10 microM induced membrane capacitance increases indicative of exocytosis in a concentration-dependent manner. At higher concentrations a decrease of the response was observed. Cells that were exposed to micromolar [Ca2+]i underwent morphological alterations resulting in swelling, which is indicative of cytoskeletal alterations. The presence of dibromo-BAPTA (4 mM) strongly inhibited secretion induced by GTP-gamma-S, thus hampering the contribution of G-protein-mediated stimulation. Application of the Ca2+ ionophore ionomycin resulted in transient increases in [Ca2+]i which were parallelled by Ca2+-dependent secretion. Effective buffering of the cytosolic calcium level below 1 microM abolished the secretory response. Our results show that an increase in [Ca2+]i can trigger secretion, but only if it is high and sustained. During physiological stimulation, however, secretion proceeds at [Ca2+]i below 1 microM. It is, therefore, concluded that mast cell degranulation under physiological conditions is not simply a result of an increase in [Ca2+]i, but that other second messenger systems in conjunction with calcium act synergistically in order to ensure fast and efficient secretion.
D000818:Animals; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D066298:In Vitro Techniques; D008407:Mast Cells / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D051381:Rats; D013873:Thionucleotides / Q000494:pharmacology
D013873:Thionucleotides; C053459:5,5'-dibromo-1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D004533:Egtazic Acid; D006160:Guanosine Triphosphate; D002118:Calcium