The overall objective of this project is to characterize the postnatal development of the mechanism or pathway underlying the secretion of fluid and electrolytes in salivary glands. We propose to use a preparation of dispersed cells from the submandibular gland of 1, 7, 14 and 21 day old rats to investigate in the new grant period several aspects of this pathway. In mature glands, it is now known to involve the activation of ion transport systems, which results in the transacinar movement of Na and Cl and, by the resulting osmotic gradient, of water. Other evidence indicates that stimulation of salivary glands enhances, as in a variety of other tissues, the turnover of membrane phospholipids, leading to the formation of products which act as cellular messengers. Although the exact relationship between these two components of the secretory response is not fully understood, there is suggestive evidence that they are linked through changes in cell calcium. Little is known about the appearance of the various components of this complex secretory response during salivary gland development. We propose to investigate, therefore, the following: 1) transmembrane fluxes of monovalent ions (Na, K, C1) with the aid of isotopic tracers. Uptake and efflux of these ions will be measured in the absence and in the presence of secretagogues, transport inhibitors and specific channel blockers. The kinetic properties (i.e., time courses, rates, half maximal values, etc.) and the external ionic requirements of each flux will be investigated; 2) stimulation-induced turnover of phospholipids. The time course of formation and breakdown of inositol phosphates, diacylglycerol and arachidonic acid will be investigated by chromatographic separation of radiolabeled molecules; 3) the effects of the products identified in 2) above on the release of Ca++ from intracellular stores and on Ca++ mobilization from the external environment. Both isotopic tracers (45 Ca) and the spectrofluorimetry of fura-2 will be used for this purpose. The effects of these two types of Ca++ movement on monovalent ion transport will also be investigated by measuring the ion (isotope) fluxes indicated in 1) above in the presence of Ca++ channel blockers and of substances which trap it in cell stores (i.e., TMB-8). The results of these studies will indicate whether the complex stores response operates at all stages of postnatal development and whether all its component elements become functional at the same time during this period.
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