Characterization of dopamine-induced potassium efflux in rat parotid acinar cells.

The effects of dopamine and noradrenaline on potassium efflux from rat parotid gland were studied in a perifusion system. Tissue specimens were preincubated with 86RbCl and the efflux of 86Rb+ was used as a marker for potassium efflux. Noradrenaline induced 86Rb+ efflux more effectively than dopamine. The noradrenaline-induced efflux was inhibited by alpha-adrenoceptor blockers, especially the alpha 1-antagonist prazosin. The dopamine-induced 86Rb+ efflux was blocked by alpha-adrenoceptor antagonists, non-selective dopamine antagonists and a D-1 selective dopamine antagonist. The D-2 selective drug, sulpiride, did not affect the dopamine-induced 86Rb+ efflux. The dopamine effect was abolished when reserpinized animals were used, whereas the effect of noradrenaline was unaffected. The results suggest that dopamine has a presynaptic stimulatory effect in rat parotid gland, and that the presynaptic effect on potassium efflux seems to be mediated via the D-1 receptor subtype. Whether activation of the presynaptic D-1 receptors leads to noradrenaline release, or whether the D-1 receptor is coupled to the catecholamine transporter system remains to be studied further.