IN the process of exocytosis the membranes of the secretory granule1,2 and the cell come together and an opening is formed at the point of coalescence. Thus the granule content is placed outside the cell while the other cell components remain inside. The granule or the cell membrane must undergo some activation which would bring the two structures into contact with each other prior to the actual fusion process. Such a reaction was sought for in the present study using preparations of rat salivary parotid gland in which massive enzyme secretion is readily induced by catecholamines via adenosine-3′,5′ monophosphate (cyclic AMP)3–6.

Epinephrine caused amylase secretion and K + release in rat parotid slices. Propranolol, which blocks β-receptors, inhibited amylase secretion; phentolamine, which blocks α-receptors, inhibited K + release. Since enzyme secretion was associated with fusion of secretory granules to the cell membrane and K + release was associated with vacuole formation, it could be shown that both α- and β-receptors are present in the same exocrine cell. The findings appear to exclude cyclic 3′,5′-adenosine monophosphate as an intermediate in the α-receptor response.