G alpha q/11 mediates cholecystokinin activation of the cationic conductance in rat substantia nigra dopaminergic neurons.

Using acutely isolated rat substantia nigra neurons, our previous studies indicated that sulfated cholecystokinin octapeptide (CCK-8) excites substantia nigra dopaminergic neurons by increasing the cationic conductance and that pertussis toxin-insensitive G proteins mediate CCK-8 induction of cationic currents. G alpha q and G alpha 11 are expressed in various tissues, including the brain, and likely to mediate pertussis toxin-insensitive neural signal transductions. In the present study, two different experiments were performed to test the hypothesis that G alpha q/11 mediates CCK-8 enhancement of the cationic conductance. First, we investigated the expression of G alpha q and G alpha 11 mRNAs in CCK-8-responsive substantia nigra dopaminergic neurons by combining whole-cell patch-clamp recordings with a single-cell reverse transcriptase-polymerase chain reaction assay. After CCK-8-evoked cationic currents were recorded, cellular RNA was harvested from single neurons and used as a template for the subsequent reverse transcriptase-polymerase chain reaction analysis. G alpha q and G alpha 11 mRNAs were present in all substantia nigra dopaminergic neurons that responded to CCK-8. Substantia nigra dopaminergic neurons were also internally perfused with the antibody raised against the common C-terminus of G alpha q and G alpha 11 during whole-cell recordings. CCK-8 failed to induce cationic currents after dopaminergic neurons were dialyzed with the anti-G alpha q/11 antibody. Our studies suggest that CCK-8 activation of the cationic conductance in substantia nigra dopaminergic neurons is transduced by G alpha q and/or G alpha 11.