[Receptive systems for drugs in salivary gland cells]

Investigators have demonstrated many types of receptors or acceptors for endogenous substances in salivary glands. These suggest that salivary glands contain receptive systems for many drugs. These receptors can be classified into three types based on the property of saliva secretion: (1) receptors involved in fluid secretion, (2) receptors involved in exocytosis for the protein secretion, (3) receptors involved in both types of secretion. The receptors involved in fluid secretion include the group of alpha 1B, M3, NK-1 receptors coupled with IP3; the group of beta 2 and VIP receptors coupled with cAMP; and the group of P2Z and P2U receptors coupled with the ATP-gated calcium channel. Whereas alpha 1A, beta 1, VIP, M3, insulin and H2 receptors mediate exocytosis via the cAMP-proteinkinase A pathway. Moreover, the another pathway of diacylglycerol-proteinkinase C has also been demonstrated to be involved in the exocytosis occurring via NK-1 and M3 receptors. Thus, salivary gland cells have many kinds of drug-receptor system. These receptors are all positive to fluid and/or protein exocytosis. Recently our study on the inhibitory regulation of saliva secretion have suggested the existence of GABA and the GABA-synthetic/metabolic pathway, GABA(A) receptors and benzodiazepine (BDZ) receptors of both central and peripheral types, and furthermore, the coupling of GABA(A) and the central type of BDZ receptors. These receptors are involved in decreasing fluid secretion and amylase release elicited by secretagogues. In the future, mechanisms of the intracellular transduction elicited by BDZ or GABA must be clarified.