Fluid secretion in salivary glands is modulated by changes in the cytosolic Ca], which involves internal Ca release and Ca entry from the external medium. This pr ect is directed towards understanding the processes which regulate cytosolic [Ca]. hree main areas were investigated during this reporting period:(i) regulation of phosphatidylinositolbisphosphate-specific phospholipase C (PLC), (ii) regul ion of Ca entry in salivary cells, and (iii) regulation of Ca flux in rat parotid gla basolateral membrane vesicles. In isolated rat parotid membranes we have characterized enzyme with high specificity for phosphatidylinositol- 4,5,bisphosphate, which is immun ogically distinct from the PLCbeta1 enzyme found in rat brain membranes. Agonist sti lation of this enzyme is dependent on the presence of lipids and detergent. Agonists ch as carbachol, stimulate Ca entry into parotid acini which results is sustained levation of Ca in the cytosol. However, during refill of the internal Ca pools Ca entry s not accompanied by substantial rise in cytosolic Ca. Our results indicate that w cytosolic Ca is maintained due to a highly active, thapsigargin sensitive, internal C accumulating mechanism. In a human salivary gland cell line, HSG, we have identified a C entry mechanism which is directly activated by muscarinic receptor stimulation. C sistent with our previous data with intact acini we have observed that Ca influx into ba lateral membrane vesicles is sensitive to pH and is inhibited by both hydrophobic a hydrophilic carbodiimides.
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