Saliva, a complex fluid secreted by salivary glands, is of critical importance to the health of the oral cavity. Neurotransmitter mediated calcium mobilization in salivary glands regulates the formation and secretion of saliva and is of primary importance to the salivary cell. To investigate the mechanisms regulating cytosolic calcium during secretory events, we have utilized in vitro dispersed cell and cellular membrane vesicle preparations from rat parotid glands. These studies have been directed towards understanding at a molecular level, (i) the basic mechanisms of calcium transport involved in the establishment of cellular calcium homeostasis; and (ii) the modulation of thee processes during neurotransmitter induced calcium mobilization. It has been shown previously that alpha 1-adrenergic and muscarinic receptor stimulation lead to calcium efflux from parotid cells. It was also shown that basolateral membrane vesicles isolated from parotid gland possess an ATP-dependent calcium transporter, which is one of the major systems regulating cytosolic calcium. In the present reporting period we have characterized the calcium transporting activities associated with two major membrane systems in the parotid cell. In the basolateral membrane we have (i) studied the modulation of the ATP dependent calcium transport by secondary ion movements and by membrane sulfhydryl group modification, (ii) developed a reconstituted system of this transporter in artifical lipid vesicles, (iii) established the electrogenic nature of the sodium/calcium exchanger. In the endoplasmic reticulum, we have characterized the ATP + magnesium-dependent calcium pump and its ionic correlates. We have also studied beta-adrenoreceptor mediated calcium mobilization in rat parotid cells in order to identify the signalling events leading to modification of calcium transport.
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