Effects of acetylcholine and monensin on 22Na uptake and cytosolic Ca2+ in rat submandibular salivary cells.

Cells isolated by enzymatic digestion of gland fragments were incubated in solutions with or without Ca2+ or Na+ and exposed to monensin (10 microM) or acetylcholine (1 microM). Effects on accumulation of 22Na and on cell Ca2+ (measured with fura-2) were compared. In Ca2(+)-containing medium, accumulation of 22Na was increased by the 2 drugs (23 and 20%, respectively) and their effects were additive. Tracer accumulation was also increased by the ionophore A23187. The effect of monensin was not inhibited by 1 mM amiloride, but partially inhibited by 1 mM furosemide. Acetylcholine caused a rapid increase (peak) in cell Ca2+, followed by a gradual decline, while monensin caused a gradual increase with no initial peak. In Ca2(+)-free medium, acetylcholine failed to enhance 22Na accumulation, but still caused a rapid peak in cell Ca2+, followed by a more rapid decrease to resting levels. Monensin enhanced 22Na uptake 16% and caused a gradual increase in cell Ca2+ in this medium. In a medium with no Na+ but containing 1 mM Ca2+, acetylcholine increased cell Ca2+ but no initial peak was observed; monensin caused a slight decrease in cell Ca2+ and then an increase to resting levels. These results suggest important interactions between Na+ and Ca2+ movements in salivary cells. Ca2+ mobilization may activate Na+ uptake and changes in cell Na+ may, in turn, influence Ca2+ mobilization from cell pools. Some of these interactions may involve a Na/Ca co- or counter-transport system.