Specific protein phosphorylation during stimulation of amylase secretion by beta-agonists or dibutyryl adenosine 3',5'-monophosphate in the rat parotid gland.

The present study was undertaken in order to examine the possible involvement of protein phosphorylation during beta-adrenergic stimulation in the rat parotid gland. Isolated parotid gland slices were stimulated by either isoproterenol or dibutyryl adenosine 3',5'-monophosphate (Bt2cAMP) in the presence or absence of propranolol. Amylase output was measured as a parameter for the degree of stimulation of secretion. Stimulation of secretion by either isoproterenol or Bt2AMP was associated with phosphorylation of three protein bands as revealed by sodium dodecylsulfate/polyacrylamide gel electrophoresis and autoradiography. The apparent molecular weights of the three proteins were 35,100 (protein I), 25,700 (protein II) and 20,400 (protein III). After cell fractionation by differential and gradient centrifugation, protein I was enriched in a light membrane fraction most likely corresponding to the plasma membrane as revealed by marker enzyme analysis. Proteins II and III were recovered in a denser fraction containing mainly mitochondria and rough microsomes. The effect of isoproterenol but not that of Bt2cAMP on phosphorylation of all three protein bands was completely abolished by propranolol. The different time course in the stimulation of amylase secretion by isoproterenol and Bt2cAMP respectively was reflected by corresponding differences in the time course of protein phosphorylation.