Calcium-dependent protein phosphorylation during secretion by exocytosis in the mast cell [23]

IN many secretory cells materials destined for secretion are packaged in membrane-limited granules and are extruded by exocytosis¹. This process is known to require metabolic energy and calcium^2-6. Calcium probably acts as a common mediator in stimulus-secretion coupling², but the molecular mechanisms involved are unknown. Increasing evidence that many physiological processes are regulated by phosphorylation of proteins ⁷ has led to the suggestion that calcium-dependent phosphorylation of proteins may be involved in secretory responses^8-13. We have sought evidence for this possibility in the mast cell, the rapid and extensive secretory activity of which conforms to the general pattern of exocytosis dependent on energy and calcium^4,14-20. Here we report a rapid phosphorylation of several proteins in rat peritoneal mast cells stimulated to secrete either by the classic mast cell secretagogue 48/80 (refs 15 and 21-23) or by the calcium ionophore A23187 (refs 22-25).