Depression of high-threshold calcium currents by activation of human D2 (short) dopamine receptors expressed in differentiated NG108-15 cells.

1. This study examined the regulation of calcium currents in differentiated NG108-15 cells that had been stably transfected with cDNA encoding the short isoform of the human D2 dopamine receptor. Whole cell calcium currents were recorded by nystatin-perforated patch clamp recording. 2. Transient low-threshold calcium currents elicited by depolarizations from -100 mV to -20 mV were reversibly depressed by NiCl2 (84 +/- 8% at 30 microM; n = 3) and by omega-agatoxin IVA (15 +/- 5%; 100 nM, n = 7). These currents were unaffected by hD2 receptor activation. 3. High-threshold calcium currents elicited by depolarizations from -80 mV to 0 mV were partly blocked by omega-conotoxin GVIA (67 +/- 6% at 100 nM, n = 4) and by the subsequent addition of the dihydropyridine, nisoldipine (94 +/- 3% at 1 microM). Consistent with the presence of at least two distinct types of high-threshold calcium channels, nisoldipine alone (38 +/- 15% at 1 microM, n = 6) did not preclude the inhibition caused by omega-conotoxin GVIA (69 +/- 13% at 100 nM, n = 4). The residual current was completely blocked by 100 microM CdCl2 (98.8 +/- 0.4%, n = 7). 4. In hD2-transfected cells, but not untransfected cells, high-threshold currents were depressed by quinpirole (30 +/- 4% at 100 nM; n = 15) with a pEC50 of 8.61 +/- 0.22 (n = 5), as well as by (-)-noradrenaline (28 +/- 5% at 1 microM, n = 9). Responses to both agonists were selectively antagonized by S-(-)sulpiride (100 nM) but not by the alpha-adrenoceptor antagonist, phentolamine (1O microM). The depression caused by (-)-noradrenaline was positively correlated with that of quinpirole for each cell(r2 = 0.91, slope = 0.99).5. hD2-receptor-mediated inhibition of high-threshold calcium currents was abolished by pretreatment of cells with omega-conotoxin GVIA (100 nM; n = 4). However, a component of the high-threshold current was reversibly depressed by omega-conotoxin GVIA (67% to 45% depression after 10 min wash). This current was also depressed by hD2 receptor activation (59 +/- 9% depression in 100 nM quinpirole, n = 3),and was completely blocked by nisoldipine (95 +/- 2% at 1 MicroM).6. These data demonstrate that activation of hD2(short) dopamine receptors can regulate both wconotoxinGVIA, and dihydropyridine-sensitive high-threshold calcium currents in neuroblastoma cells.Morever, the ability of human D2 dopamine receptors to regulate more than one type of calcium current supports the notion that these receptors have a diverse functional role in the central nervous system.