Identification of cellular activation mechanisms associated with salivary secretion.

In recent years, our understanding of receptor-signalling mechanisms in the salivary glands has advanced considerably. Two receptor pathways exist, one involving cAMP, which primarily regulates enzyme secretion, and another involving the hydrolysis of PIP2, which regulates Ca2+ mobilization and, subsequently, monovalent ion fluxes probably important in ion and water secretion in the intact gland. Mobilization of Ca2+ results from both the release of internal Ca2+, and from Ca2+ entry from the extracellular space. The signal for Ca2+ release appears to be (1,4,5)IP3, one of the water soluble products of PIP2 hydrolysis. The mechanism controlling Ca entry is not understood, but speculation abounds. Hydrolysis of PIP2 also produces DG, which has a messenger role in activating a specific protein kinase, the C kinase. The C kinase interacts with Ca2+ mobilization in some as yet uncharacterized way in regulating enzyme secretion.