REGULATION OF WATER TRANSPORT VIA PARACELLULAR PATHWAY BY PHOSPHORYLATION AND DEPHOSPHORYLATION IN SALIVARY GLASNDS

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The relationship between neurokinin A-or pilocarpine-provoked salivary fluid secretion and paracellular transport by using Lucifer Yellow was investigated in perfused rat submandibular gland. Salivary fluid secretion provoked by neurokinin A-or pilocarpine was dependent on the increase in intracellular Ca^<2+> concentrations, which was linked to Lucifer Yellow secretion. These results suggest that Ca^<2+>-dependent phosphorylation and/or dephosphorylation appears to contribute to the paracellular transport. On the other hand, expression and localization of tight junction proteins was induced by insulin-like growth factor I(IGF-I) in cultured rat submandibular gland cells, suggesting that IGF-I contributes to maintenance of the paracellular pathway system in salivary gland. Since the IGF-I effect was inhibited by PI3-kinase inhibitors, phosphorylation by PI3-kinase appears to contribute to the effect of IGF-I.