Effects of carbachol on extracellular Na-dependent AIB uptake in rat parotid gland

In rat parotid glands the uptake of 2-[1-14C]aminoisobutyric acid (AIB), in vitro, depends on a Na concentration gradient between the intra- and extracellular medium. Ouabain (1 mM) which inhibits the Na+-K+-ATPase and a Na+ ionophore, monensin (which dissipates the Na+ gradient), both suppress this amino acid uptake. Carbachol (5 microM) (through muscarinic receptors) evokes a decrease in AIB uptake, and in the presence of 0.1 mM ouabain the cholinergic effect is enhanced. Ouabain alone (0.1 mM) very slightly depresses the [14C]AIB uptake. Neither 1 microM isoproterenol, nor 1 microM Ca2+ ionophore A23187, which affect the membrane potential in rat parotid acinar cells, modifies the AIB uptake. When the Ca is removed from the incubation medium, carbachol still evokes a small decreasing effect on AIB uptake. From these data we can suggest that the reduced AIB uptake (induced by the cholinergic agonist) appears to be related to a process dependent on variation of intracellular Na concentration that may be triggered by the cholinergic agonist.