Subcellular distribution and activation of rat submandibular cAMP-dependent protein kinase following beta-adrenergic receptor stimulation.

The extent of activation of rat submandibular protein kinase A (EC 2.7.1.37) isozymes following beta-adrenergic receptor stimulation was determined in vitro using dispersed cells and an 8-N3-[32P]cAMP photoprobe. The half-maximal binding of the photoprobe for microsomal and cytosolic type I and cytosolic type II was 9 nM, 27 nM and 92 nM, respectively. 'Cold trap' studies indicated that 70% of type I protein kinase A was activated following maximal beta-adrenergic receptor stimulation, whereas type II activation was less than 40%. Both cytosolic and microsomal type I activation occurred rapidly following beta-adrenergic receptor stimulation and both remain activated throughout the entire secretory period. Type I inactivation occurred rapidly subsequent to beta-adrenergic receptor blockade. The dose-response relationship for the isotypes following beta-adrenergic receptor activation demonstrated a greater extent of type I activation at submaximal concentrations of agonist. Although protein kinase A may not be the only kinase involved in rat submandibular mucin release, these data add further support to a direct regulatory role for this kinase, with type I having potentially a greater role than type II.