MUSCARINIC SIGNALING PATHWAY IN SUBMANDIBULAR CELLS OF ADULT AND EARLY POSTNATAL RATS

Elements of the muscarinic signal transduction pathway were compared i n submandibular acinar cells of 1-day-old, 1-week-old, and adult rats after exposure to concentrations of acetylcholine ranging from 0.05 to 10 mu M. Formation of inositol trisphosphate (IP3) and intracellular Ca2+ were comparable in cells from the three age groups after exposure to agonist concentrations <1 mu M. At higher agonist concentrations, IP3 generation and peak initial changes in [Ca2+](i) were significantl y greater in cells of newborn animals. In cells of 1-week-old animals, increased peak [Ca2+](i) responses were seen even at low agonist conc entrations, although IP3 production was not increased when compared wi th fully mature cells. Increased initial [Ca2+](i) peaks, but comparab le subsequent plateau [Ca2+](i) values, were seen in the immature cell s in both Ca2+-containing and Ca2+-free solutions. Permeabilized cells of early postnatal animals took up less Ca-45(2+) into nonmitochondri al Ca2+ pools in the presence of 1.5 mM ATP and also released less tra cer in response to intermediate IP3 concentrations than adult cells. D eveloping salivary cells thus show differences in important functional linkages of the muscarinic signal transduction pathway, including tho se between receptor activation and phosphoinositide turnover and betwe en IP3 and release of internally stored Ca2+ Differences in the Ca2+ s tores or in their sensitivity to IP3 may account for the latter observ ation. Immature salivary cells seem to have adequate mechanisms for Ca 2+ entry.