adp-beta-s and Pinealoma

Rhythmic noradrenergic signaling from the hypothalamic clock in the suprachiasmatic nucleus to the pineal gland causes an increase in intracellular cAMP which regulates the circadian fluctuation of melatonin synthesis. The activation of phospholipase C (PLC)-coupled P2Y(2) receptors upon treatment with ATP and UTP exclusively inhibited the isoproterenol-stimulated cAMP production in mouse pineal gland tumor cells. However, the activation of other PLC-coupled receptors including P2Y(1) and bombesin receptors had little or no effect on the isoproterenol-stimulated cAMP production. Also, ATP did not inhibit cAMP production caused by forskolin, prostaglandin E(2), or the adenosine analog NECA. These results suggest a selective coupling between signalings of P2Y(2) and beta(2)-adrenergic receptors. The binding of [(3)H]CGP12177 to beta(2)-adrenergic receptors was not effected by the presence of ATP or UTP. Ionomycin decreased the isoproterenol-stimulated cAMP production, whereas phorbol 12-myristate 13-acetate slightly potentiated the isoproterenol response. Chelation of intracellular Ca(2+), however, had little effect on the ATP-induced inhibition of cAMP production, while it completely reversed the ionomycin-induced inhibition. Treatment of cells with pertussis toxin almost completely blocked the inhibitory effect of nucleotides. Pertussis toxin also inhibited the nucleotide-induced increase in intracellular Ca(2+) and inositol 1,4,5-trisphosphate production by 30-40%, suggesting that the ATP-mediated inhibition of the cAMP generation and the partial activation of PLC are mediated by pertussis toxin-sensitive G(i)-protein. We conclude that one of the functions of P2Y(2) receptors on the pineal gland is the selective inhibition of beta-adrenergic receptor-mediated signaling pathways via the inhibitory G-proteins.

Topics: 1-Methyl-3-isobutylxanthine; Adenosine Diphosphate; Adenosine Triphosphate; Adenylyl Cyclases; Adrenergic beta-Agonists; Animals; Bombesin; Calcium; Cyclic AMP; Extracellular Space; Isoproterenol; Mice; Pertussis Toxin; Phosphodiesterase Inhibitors; Pinealoma; Propanolamines; Receptors, Adrenergic, beta-2; Receptors, Purinergic P2; Receptors, Purinergic P2Y2; Signal Transduction; Thionucleotides; Tritium; Tumor Cells, Cultured; Uridine Triphosphate; Virulence Factors, Bordetella