Saliva is the principle protective agent for the mouth and thus is of primary importance to oral health maintenance. Perturbations in the salivary secretory mechanism can consequently lead to serious oral health problems. The objective of this project is to study the membrane and cellular processes which underlie the phenomenon of primary fluid secretion by salivary acinar cells to contribute to our understanding of the fluid secretory process in normal and diseased states. Because similar secretory mechanisms are thought to be common to a number of other exocrine glands, this information should be of rather broad applicability and interest. During the present reporting period our specific areas of focus were the following. (1) The transport of ions (Na, K, Cl), whose transmembrane and transepithelial movements are involved in primary salivary fluid secretion, was studied in vitro in a rat parotid acinar suspension and/or in isolated rabbit and rat parotid basolateral membrane vesicles. (2) Intracellular events (changes in calcium concentration, electrical potential and cell volume) associated with muscarinic cholinergic stimulation of individual parotid acini were studied using electrophysiological techniques and digital video imaging microscopy. (3) The bumetanide binding properties of a Na/K/Cl cotransporter in the rabbit parotid basolateral membrane were characterized. This transporter plays a major role in fluid secretion in a number of exocrine glands. (4) The rabbit parotid Na/K/Cl cotransporter was solubilized and partially purified using conventional protein separation procedures. (5) Primary cultures of parotid acinar cells grown in defined media were studied in order to establish minimal requirements for cell viability, proliferation and differentiation.
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