Parotid gland in rats, a model for the study of regulated exocrine secretion

In rat parotid glands protein secretion studied in vitro is weakly stimulated by carbachol (which induces Phospholipase C activation) and strongly by isoprenaline (which activates the adenylate cyclase system). We show in this work that the simultaneous activation of the two types of receptors induces a potentiation of protein secretion. This is not 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 phenomenon is a post-receptor event which takes place at a distal step from messenger production. Furthermore we also showed that the activation of beta-adrenergic receptor led to two parallel events: cAMP accumulation and calcium movements. These two events were required to obtain maximal secretion. We also show that cholinergic induced secretion is also the result of a synergism between calcium and protein kinase C activation. At a physiological level, the synergism between two different transduction pathways must play an important role. This surely allows the cells to give maximal response, without any desensitization phenomena.