Dopamine induces hyperpolarization of locust salivary gland acinar cells via D1-like receptors.
The effect of dopamine on the salivary gland acinar cells of the locust was examined using conventional intracellular recording techniques. Application of dopamine induced a reversible, dose-dependent hyperpolarization of the acinar cells, with an EC50 of 0.1 μM dopamine. We investigated the pharmacology of the dopamine receptor mediating hyperpolarization of the acinar cells using a range of dopaminergic agonists and antagonists. The effect of dopamine could be mimicked by the selective D1 receptor agonist SKF82958, whilst the D2 receptor agonists PPHT–HCl and TNPA–HBr were far less potent at inducing hyperpolarization. The receptor also showed selectivity to certain synthetic D1-like agonists. SKF82958 was much more effective at inducing a hyperpolarization than SKF81297. The dopamine-induced hyperpolarization of locust acinar cells could be blocked using the selective D1 receptor antagonist SCH23390 whilst the D2 receptor antagonists sulpiride and spiperone were inactive. The rank order of potency of several dopaminergic agonists and antagonists was obtained and suggests that the dopamine receptor mediating the hyperpolarization in locust salivary gland acinar cells is similar to a mammalian D1 receptor. Stimulation of the salivary nerve mimicked the effect of dopamine on the acinar cells, inducing a rapid reversible hyperpolarization. This neurally-evoked hyperpolarization of the locust acinar cells was suppressed using 1.0 μM SCH23390, whilst 10 μM sulpiride was inactive. This demonstrated that both exogenously applied dopamine and endogenously released dopamine are probably acting on the same receptor