Secretion in mast cells induced by calcium entrapped within phospholipid vesicles.

Purified mast cells secreted histamine when fused to phospholipid vesicles containing calcium but not magnesium or potassium. Microscopic observation revealed highly localized exocytotic responses involving punctate extrusion of individual granules. Calcium delivered from the vesicles to the cytoplasm is apparently a sufficient stimulus to initiate exocytosis. The results support the calcium hypothesis of stimulus-secretion coupling.