RAT PAROTID-GLAND, GOOD MODEL TO STUDY RE GULATED EXOCRINE SECRETION

In rat parotid glands protein secretion studied in vitro. is weakly st imulated by carbachol (which induces Phospholipase C activation) and s trongly by isoprenaline (which activates the adenylate cyclase system) . We show in this work that the simultaneous activation of the two typ es of receptors induces a potentiation of protein secretion. This is n ot due to an enhanced IP3 or cAMP accumulation nor any modification on calcium movements. Potentiation of protein secretion is also mimicked by analogues of second messengers suggesting that this phenomenum is a post-receptor event which takes place at a distal step from messenge r production. Furthermore we also showed that the activation of beta-a drenergic receptor led to two parallel events: cAMP accumulation and c alcium movements. These two events were required to obtain maximal sec retion. We also show that cholinergic induced secretion is also the re sult of a synergism between calcium and protein kinase C activation. A t a physiological level, the synergism between two different transduct ion pathways must play an important role. This surely allows the cells to give maximal response, without any desensitization phenomena.