Calcium and stimulus‐secretion coupling in the mast cell: stimulant and inhibitory effects of calcium‐rich media on exocytosis

Abstract

Isolated rat peritoneal mast cells incubated in Ca-free media for 2 h, with or without EDTA, and observed by phase-contrast microscopy, became bubbled in appearance when subsequently exposed to media rich in Ca (16-110 mM). EM showed the response to be compound exocytosis of the sort elicited by conventional mast cell secretagogues such as antigen (in sensitized cells) and 48/80. The response to Ca was inhibited by withdrawing glucose and adding dinitrophenol and was thus energy-dependent. Mg in similarly high concentration had no such stimulant effect on Ca-deprived cells, and excess Ca stimulated only after Ca deprivation. Ca deprivation may increase the permeability of the plasma membrane of the mast cell thereby allowing some Ca, when subsequently introduced in high concentration, to penetrate and activate exocytosis. The results may provide further support for the postulated mediator function of Ca in stimulus-secretion coupling. Two inhibitory effects of Ca in high concentration were detected: suppression of migration or expulsion of granules from the exocytotic pits within the cellular domain; and diminished sensitivity to 48/80 [condensation product of 4-methoxy-N-methyl-benzeneethanamine and formaldehyde].