A novel role for dopamine: inhibition of muscarinic cholinergic-stimulated phosphoinositide hydrolysis in rat brain cortical membranes.

Dopamine inhibited phosphoinositide breakdown as stimulated by carbachol in rat brain cortical membranes. The IC50 value was 14 +/- 2 microM for dopamine's inhibition of phosphatidylinositol hydrolysis as stimulated by 1 mM carbachol. The inhibition was found at low (0.1 microM), but not high (greater than 0.3 microM), concentrations of the non-hydrolyzable guanine nucleotide analog, GTP gamma S. Pharmacological characterization of the response indicated that the dopamine effects were mediated by D1 receptors. The assay conditions precluded any involvement of cyclic-AMP as a mediator of the dopamine response, and thus, a novel role is proposed for dopamine in cortex working through D1 receptors to inhibit phosphoinositide degradation.