Ca2+ mobilization and Cl efflux in submandibular salivary cells of adult and newborn rats.

These cells were isolated by enzymatic digestion from glands of 1-day-old and fully mature rats. The effects of exposure to acetylcholine on cytosolic Ca2+ and Cl efflux were studied by, respectively, spectrofluorimetry of fura-2 and the net efflux of the isotopic tracer 36Cl from preloaded cells. In both types of cells, when incubated in Ca2+-containing solutions, acetylcholine initially caused a rapid, significant increase in cytosolic Ca2+ (from approx. 90 to 480-570 nmol), followed by a slower decrease to a plateau value of 280-290 nmol. The initial peak persisted (315-339 nmol) in Ca2+-free solutions but the cytosolic Ca2+ concentrations decreased rapidly to levels below prestimulation values (30 nmol). 36Cl efflux in tracer preloaded cells incubated in Ca2+-containing medium in the presence of acetylcholine was 18% in cells of new born animals and 35% in adult cells. In Ca2+-free medium, mature cells showed a transient but significant (26%) efflux of 36Cl. Cells of 1-day-old rats did not show a net efflux of 36Cl under these conditions, but subsequent addition of Ca2+ caused a 15% reduction (i.e. efflux) in tracer content. The antagonist 3,4,5-trimethoxybenzoate-8(N,N-dithylamino)octyl ester (TMB 8), which blocks internal Ca2+ release, inhibited both the initial increase in cell Ca2+ in both types of cells and the transient efflux of 36Cl seen in mature cells when incubated in Ca2+-free solutions. At high concentrations (5 mM), LaCl3 inhibited efflux of 36Cl in mature cells but not in those of newborn rats. However, at lower concentrations (0.1 mM), which do not interfere with fluorescence spectra, LaCl3 did not inhibit the effect of acetylcholine on cell Ca2+. These results suggest that Cl efflux in adult submandibular cells is regulated by an increase in cell Ca2+ arising from release of internal Ca2+ and from influx of external Ca2+. Both of these responses are evident in cells of newborn animals but Cl efflux is either decreased or absent. This is likely to be associated with a deficiency in the Cl channels or in the coupling between Ca2+ and the channel substrate through regulatory molecules associated with phosphorylation of the channel protein.