ergoline and Glioma

Topics: Animals; Cell Division; Cell Line; Cyclic AMP; Dopamine Agonists; Ergolines; Gene Expression; Glioma; Models, Biological; Naphthalenes; Neuroblastoma; Neurotensin; Nucleus Accumbens; Pyrrolidines; Quinpirole; Receptors, Dopamine D2; Receptors, Dopamine D3; Recombinant Proteins; Transfection

This study describes the depression of calcium currents caused by activation of human D3 dopamine receptors which have been stably expressed in the neuroblastoma x glioma NG108-15 cell line. Transfected cells, which had been differentiated with prostaglandin E1 and isobutylmethylxanthine, exclusively expressed D3 receptor mRNA, which was demonstrated by reverse transcription polymerase chain reaction techniques. Transfected cells had high affinity binding sites for iodosulpiride, with a Kd of 0.8 nM and receptor density of 240 fmol mg-1 protein. Calcium currents were recorded using nystatin-perforated patch clamp techniques. In contrast to untransfected cells that had been differentiated, high-threshold calcium currents in differentiated hD3-NG108-15 cells were depressed by application of dopamine and quinpirole. These responses were abolished by the dopamine receptor antagonist S-(-)-sulpiride (1 microM), demonstrating that they were caused by the activation of the transfected dopamine receptors. Coupling of human D3 receptors to calcium currents was sensitive to the action of pertussis toxin, suggesting the involvement of G-proteins of the Gi and/or G(o) subtype. These results demonstrate that human D3 receptors represent a functional class of dopamine receptor.

Topics: Brain Neoplasms; Calcium Channel Blockers; Calcium Channels; Cell Differentiation; Dopamine Agents; Ergolines; Glioma; GTP-Binding Proteins; Humans; Neuroblastoma; Polymerase Chain Reaction; Quinpirole; Receptors, Dopamine; Receptors, Dopamine D2; Receptors, Dopamine D3; RNA, Messenger; Sulpiride; Tumor Cells, Cultured

Transfection of a human dopamine D3 receptor cDNA in a neuroblastoma-glioma hybrid cell line (NG 108-15) provided clonal cell lines stably expressing up to 600 fmol per mg protein of [125I]iodosulpiride binding sites. Dopamine and several agonists distinguished two receptor-affinity states in membranes. In the case of dopamine, the high-affinity state (Ki = 0.9 nM, 30% of total binding) was completely converted into a low-affinity state (Ki = 57 nM) in the presence of 10 microM guanosine-5'-O-(3-thiotriphosphate). In addition to these two sites, a site with a very low affinity for dopamine was evidenced in whole cells. The dopamine D3 receptor mediated two responses: c-fos activation, as measured by the appearance of Fos-like immunoreactivity, and increased mitogenesis, as measured by incorporation of [3H]thymidine. The Fos-like immunoreactivity appeared within 30 min, lasted 2 h and was blocked by the partially selective dopamine D3 receptor compound (+)-UH 232 (cis-(+)-5-methoxy-1-methyl-2-(di-n-propylamino)tetralin). The mitogenic effect, which occurred after a lag time (over 2 h stimulation), was produced with subnanomolar potency and full intrinsic activity by several compounds previously identified as dopamine D2 receptor agonists, e.g. quinpirole, (+)-7-OH-DPAT ((+)-7-hydroxy-2-(di-n-propylamino)tetralin) and RU 24926 (N-n-propyl-di-beta(3-hydroxyphenyl)-ethylamine), and was reversibly blocked by (+)-UH 232 (Ki = 9 nM). Talipexole (B-HT 920, 5-allyl-2-amino-5,6,7,8-tetrahydro-4H-thiazolo[4,5-d]azepin) was identified as a partial agonist at the dopamine D3 receptor. Dopamine D3 receptor-mediated mitogenesis was potentiated by a phorbol ester and was abolished by pretreatment with pertussis toxin. A mitogenic effect of same amplitude was elicited by bradykinin or carbachol, both acting through constitutive receptors. Bradykinin markedly activated inositol phosphate turnover, and had no effect on forskolin-stimulated cyclic AMP accumulation. Carbachol inhibited forskolin-stimulated cyclic AMP accumulation and had no effect on inositol-phosphate turnover. Quinpirole had no effect on any of these second messenger pathways. Thus, in transfected NG 108-15 cells, the dopamine D3 receptor is coupled to a pertussis toxin-sensitive G protein and mediates two possibly unrelated biological effects, through initial biochemical events that remain to be identified.

Topics: Animals; Cyclic AMP; Ergolines; Genes, fos; Glioma; GTP-Binding Proteins; Guanosine 5'-O-(3-Thiotriphosphate); Humans; Hybrid Cells; Mice; Neuroblastoma; Quinpirole; Rats; Receptors, Dopamine; Receptors, Dopamine D2; Receptors, Dopamine D3; Sulpiride; Thymidine; Transfection; Tumor Cells, Cultured

Two isoforms of the D2 dopamine receptor exist, termed D2 short (D2s) and D2 long, which differ by the presence or absence of 29 amino acids. To examine the possible coupling of the D2s isoform to voltage-dependent K+ current, NG108-15 cells that were transfected with and stably express this isoform were studied using whole-cell patch-clamp techniques. In transfected, but not untransfected, cells dopamine and quinpirole (QUIN) reduced the normally observed peak outward K+ current, and this effect was abolished by the D2 antagonist sulpiride but not by the alpha 2-adrenergic receptor antagonist idazoxan or the D1 antagonist (R)-(+)-SCH-23380. The D1 receptor agonist SKF 38393 had no effect. QUIN-induced inhibition of K+ current was prevented by loading the cells with the Ca(2+)-chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, suggesting a critical role for intracellular Ca2+ mobilization. In contrast, reduction of the concentration of extracellular Ca2+ and inclusion of the Ca2+ channel blocker cobalt did not modify the reduction of K+ current produced by stimulation of D2s receptors. A critical role for intracellular calcium mobilization in the observed effects was further supported by the observation that increases in cytosolic Ca2+ produced by thapsigargin mimicked the effect of QUIN, whereas intracellular ryanodine, which blocks Ca2+ mobilization, abolished the QUIN responsiveness. Finally, the effect of D2S activation on K+ current was not modified by pretreatment of the cells with pertussis toxin. These results suggest that the D2s dopamine receptor expressed in NG108-15 cells inhibits the activity of native K+ current via a mechanism that is dependent upon the mobilization of intracellular Ca2+ and does not involve a pertussis toxin-sensitive G protein.

Topics: Calcium; Dopamine; Ergolines; Glioma; GTP-Binding Proteins; Hybrid Cells; Membrane Potentials; Neuroblastoma; Neurons; Pertussis Toxin; Potassium Channels; Quinpirole; Receptors, Dopamine D2; Recombinant Proteins; Tumor Cells, Cultured; Virulence Factors, Bordetella

A microphysiometer was used to quantify the rate of extracellular acidification by C6 glioma cells and L fibroblasts expressing recombinant dopamine D2 receptors. The dopamine D2 receptor agonist, quinpirole, accelerated the rate of acidification of the medium by C6 cells expressing either the short or long form of D2 receptors, D2(415) and D2(444), but not by wild-type cells that were not transfected with a D2 receptor cDNA. The rate of acidification increased with increasing concentrations of quinpirole up to 100 nM. Inhibition of the response by the dopamine D2 antagonist, spiperone, provided additional evidence that the enhanced extracellular acidification resulted from stimulation of D2 receptors. To test the hypothesis that D2 receptor-stimulated extracellular acidification was due to transport of protons by a Na+/H+ antiporter and reflected intracellular alkalinization, the effect of two inhibitors of Na+/H+ exchange, amiloride and methyl-isobutyl-amiloride, was determined. Both compounds inhibited quinpirole-induced extracellular acidification at concentrations that did not alter D2 receptor-mediated inhibition of adenylylcyclase or radioligand binding to D2 receptors. In addition, quinpirole-induced extracellular acidification was greatly inhibited by removal of sodium from the extracellular medium, confirming the participation of Na+/H+ exchange in the extrusion of acid. Quinpirole (100 nM) also increased the rate of extracellular acidification by L cells expressing D2(415), LZR1 cells. Treatment with pertussis toxin (100 ng/ml for 18 h) had no effect on the quinpirole-induced acid extrusion by C6D2(415) and LZR1 cells, although the same pertussis toxin treatment regimen completely prevented inhibition of adenylylcyclase. We conclude that recombinant D2 receptors accelerate Na+/H+ exchange in C6 cells and L fibroblasts by a pathway that does not involve inhibition of adenylylcyclase or pertussis toxin-sensitive G proteins.

Topics: Amiloride; Animals; Carrier Proteins; Dopamine Agents; Dose-Response Relationship, Drug; Ergolines; Glioma; Hydrogen-Ion Concentration; Kinetics; Quinpirole; Rats; Receptors, Dopamine D2; Recombinant Proteins; Sodium; Sodium-Hydrogen Exchangers; Spiperone; Tumor Cells, Cultured