Calcium-mediated effects of carbachol on cation pumping and Na uptake in rat parotid gland

Abstract

Carbachol (10(-4) M), a cholinergic secretagogue, significantly increased the ouabain-sensitive uptake of 86Rb by rat parotid gland slices. This effect was blocked by the omission of Ca from the bathing medium. When extracellular Na was decreased from 125 to 5 mM, the effect of carbachol was reversed (86Rb uptake was significantly decreased). Increasing intracellular Na (by incubation in medium lacking K) produced a significant stimulation of 86Rb influx. A role for Na in the response was suspected, and so the metabolism, of 22Na by the slices was characterized. The 60-minute distribution of 22Na could be described by three kinetic components; one extracellular (0.315 ml/g, tau = 1.94 minutes) and two intracellular (0.075 ml/g, tau = 7.63 minutes and 0.017 ml/g, tau = 58.4 minutes). Carbachol enhanced the uptake of 22Na into the intracellular components (primarily the 7.63-minute component). The increased uptake of 22Na required Ca in the bathing medium. These observations could be explained by assuming that cholinergic receptor activation stimulates Ca influx which in turn enhances Na uptake. The resulting elevated intracellular Na acts to stimulate activity of the Na,K pump.