The health of the oral cavity is maintained by salivary secretions. The pr cipal function of salivary glands is to produce these complex fluids. We utilize n vitro dispersed cells of salivary glands to understand mechanisms controlling sal a formation. We have focused our studies on neurotransmitter regulation of secretory eve s and associated signalling mechanisms. During this reporting period the primary ocus of study continues to be muscarinic receptors (mAChRs) in rat parotid gland acinar c ls and their coupling to functional responses via specific G proteins. We have also ini ated studies of alpha-adrenergic receptors (alpha1-ARs) in these cells. In parotid cell stimulation of mAChRs results in the generation of inositol phosphates via the activati of a phosphatidylinositol 4,5-bisphosphate specific phospholipase C. Subsequent this response leads to the elevation of cytosolic Ca2+ levels and fluid secretio Additionally, mAChRs can mediate the inhibition of agonist induced cAMP for tion. We have characterized the binding of a subtype non-selective antagonist (quinu idinyl benzilate, QNB) to mAChRs in intact rat parotid cells. Specific binding is aturable, time- and temperature-dependent (Bmax approximately 80 fmol/mg protein; Kd proximately 100 pM). Also, we have assessed the relationship between mAChR occupancy a second messenger formation, determining that a moderate population (approximately -40%) of spare receptors exist for inositol trisphosphate (IP3) formation. We previ sly reported that rat parotid M3-mAChRs couple to two different signal transducing G pro ins. This year we determined the nucleotide sequence encoding the region of this rece or gene involved in G-protein coupling and we observed that it is virtually identic to other reported 3 sequences. Thus, the mAChR itself is unlikely to be responsibl for the divergent coupling. Additionally, we have shown that the alpha1-adrenergic eceptor subtype involved in the fluid secretory response is alpha1A.
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