Effects of stimulation of muscarinic and of β-catecholamine receptors on the intracellular distribution of protein kinase C in guinea pig exocrine glands

Abstract

Stimulation of exocrine cells via muscarinic receptors is associated with an activation of protein kinase C [Padel & Soling (1985) Eur. J. Biochem. 151, 1-10]. We show here that stimulation of isolated parotid gland lobules with 8 x 10-6 M-carbamoylcholine leads to a translocation of protein kinase C from the cytosolic to the particulate compartment within 30 s (25% and 45% of total activity recovered in the particulate fraction of controls and stimulated samples respectively). The specific enzyme activity in the particulate fraction increased to 169% of the corresponding control value. After 10 min the changes started to reverse and, after 30 min, cytosolic protein kinase C was higher in stimulated than in unstimulated lobules. Isoproterenol (2 x 10-5 M) stimulated the release of amylase more than did carbamoylcholine, but did not significantly affect intracellular distribution of protein kinase C during the observation time of 30 min. In isolated pancreatic lobules a significant carbamoylcholine-mediated translocation of protein kinase C into the particulate fraction could be observed after 5 and 20 min, but not after 1 min. After 5 min the specific enzyme activity in the particulate fraction had increased to 153% of the corresponding controls. The corresponding decrease (-38%) in the specific enzymic activity of cytosolic protein kinase C stayed constant up to 30 min. In isolated parotid gland lobules α-amylase secretion proceeded at a linear rate already during the first 1 min of stimulation, whereas in pancreatic lobules a measurable rate of α-amylase secretion did not occur before 5 min. These differences in time course paralleled the differences in the onset of translocation of protein kinase C. The results support a direct involvement of protein kinase C in carbamoylcholine-mediated but not in isoproterenol-mediated stimulation of exocytosis in exocrine cells.