The proper functioning of salivary glands is essential to the maintenance of oral health. The list of identified extracellular agents implicated in regulating salivary gland secretion continues to increase. Recent additions include extracellular nucleotides, working through P2 purinoceptors. While a role for ligand-gated ion channel P2 receptors in salivary glands has been known for several years, the presence and activity of G protein-coupled (GPC) P2 receptors in the glands has been less easily documented, although these receptors are present in cell lines of salivary origin. The studies proposed in this application are based on our recent cloning and expression of the first cDNA for a human P2 purinoceptor, the GPC P2U subtype and on initial studies of P2 receptor activity in normal rat submandibular gland (SMG) cells. The hypothesis to be tested is that the GPC P2 purinoceptor subtypes, P2U and P2Y, are involved in the regulation of salivary gland secretion and that the expression and activity of these receptors vary as a function of the state of development and organization of the glands and as a consequence of exposure to agonist. It is also hypothesized that rat SMG cells express volume-sensitive chloride channels that are involved in the regulatory volume decrease potentiated by P2 receptor agonists in cells of salivary origin.
The specific aims are: 1) to assess development-related changes in the expression and regulatory role of P2U and P2Y purinoceptors in rat salivary glands, using gland cells isolated from animals of different ages; 2) to examine the effects of disruption of normal salivary gland structure on P2U and P2Y receptor expression and activity; 3) to characterize agonist-induced desensitization of P2 receptors and to evaluate the role in desensitization of consensus phosphorylation sites within these receptors; and 4) to evaluate, through cloning and expression of its cDNA, the contribution of volume-sensitive chloride channels in HSG-PA salivary cells to regulatory volume decrease (RVD), a process potentiated by P2U receptor activation. Together, these studies will provide a fuller appreciation of the role that P2 receptors play in the regulation of salivary secretion and of the factors involved in the expression and activity of these receptors. The ultimate goal is to elucidate the contributions salivary P2 receptors make to the maintenance of oral health.
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