Rat parotid gland protein kinase activation. Relationship to enzyme secretion

The degree of activation of rat parotid gland cyclic AMP-dependent protein kinase (EC 2.7.1.37) was measured in tissue minces in vitro in order to assess the involvement of this enzyme in the parotid stimulus-secretion coupling mechanism. Kinase activation, determined by the activity ratio method, was measurably increased by isoproterenol, a beta-adrenergic agonist and a potent stimulator of alpha-amylase (EC 3.2.1.1) secretion. Muscarinic cholinergic and alpha-adrenergic stimulation, less effective in releasing amylase, did not affect protein kinase activation. Kinase activation closely paralleled the cyclic AMP concentration when the concentration of isoproterenol was varied. Amylase release exhibited a similar isoproterenol dose-dependence, except that amylase release was measurably increased at an isoproterenol concentration slightly lower than that required to increase detectably the cyclic AMP concentration or kinase activation. Partial dissociation between cyclic AMP levels, kinase activation, and secretion was seen when submaximal beta-adrenergic stimulation was combined with submaximal and supramaximal cholinergic stimulation. These results suggest an involvement of cyclic AMP-dependent protein kinase in beta-adrenergic-stimulated amylase release, but show that the extent of secretion is not rigidly coupled to the extent of kinase activation as determined by the activity ratio method. Protein kinase activation may function in concert with other factors in the regulation of exocytosis in this tissue.