Phosphorylation of the same specific protein during amylase release evoked by beta-adrenergic or cholinergic agonists in rat and mouse parotid glands.

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Abstract
Stimulation of amylase secretion from the rat parotid gland by .beta.-adrenergic agonists is associated with a specific phosphorylation of 3 membrane-bound proteins designated as proteins I, II, and III. Stimulation by carbachol induced significant phosphorylation of only protein I. This phosphorylation was low compared to isoproterenol-induced phosphorylation but corresponded to the smaller enhancement of amylase secretion. The mouse organ is almost equally sensitive to .beta.-adrenergic and to cholinergic agonists. Incubation of mouse parotid gland slices with 20 .mu.M isoproterenol or 10 .mu.M carbachol resulted in strong and comparable releases of amylase, which were accompanied by comparable phosphorylations of protein I. Proteins II and III were phosphorylated only in the presence of isoproterenol. Removal of external Ca by ethylene glycol bis (.beta.-aminoethyl ether)-N,N,N'',N''-tetraacetate abolished the carbachol-induced release of amylase but not the phosphorylation of protein I. Isoproterenol-induced secretion of amylase and phosphorylation of proteins I, II and III were not inhibited under these conditions. Amylase release stimulated by the ionophore A-23187 was accompanied by the phosphorylation of protein I. Two-dimensional electrophoresis revealed that the radioactive spot corresponding to protein I was located at the same position after cholinergic and after .beta.-adrenergic stimulation, indicating that both stimuli led to the phosphorylation of the same membrane-associated protein. The phosphorylation of protein I is apparently an important step in the sequence of events leading from receptor activation to exocytosis.