Selective stimulation of catecholamine release from bovine adrenal chromaffin cells by an ionotropic purinergic receptor sensitive to 2-methylthio ATP.
BACKGROUND
2-Methylthioadenosine 5'-triphosphate (2-MeSATP), formerly regarded as a specific P2Y (metabotropic) purinergic receptor agonist, stimulates Ca2+ influx and evokes catecholamine release from adrenal chromaffin cells. These cells express P2Y and P2X (ionotropic) purinoceptors, with the latter providing an important Ca2+ influx pathway. Using single cell calcium imaging techniques, we have determined whether 2-MeSATP might be a specific P2X receptor agonist in bovine chromaffin cells and assessed the relative role of P2X and P2Y receptors on catecholamine secretion from these cells.


RESULTS
ATP raised the [Ca2+]i in ~50% of the cells. Removing extracellular Ca2+ suppressed the [Ca2+]i-raising ability of 2-MeSATP, observed in ~40% of the ATP-sensitive cells. This indicates that 2-MeSATP behaves as a specific ionotropic purinoceptor agonist in bovine chromaffin cells. The 2-MeSATP-induced [Ca2+]i-rises were suppressed by PPADS. UTP raised the [Ca2+]i in ~40% of the ATP-sensitive cells, indicating that these expressed Ca2+-mobilizing P2Y receptors. UTP-sensitive receptors may not be the only P2Y receptors present, as suggested by the observation that ~20% of the ATP-sensitive pool did not respond to either 2-MeSATP or UTP. The average sizes of the ATP- and 2-MeSATP-evoked [Ca2+]i responses were identical in UTP-insensitive cells. 2-MeSATP stimulated Ca2+ influx and evoked catecholamine release, whereas UTP elicited Ca2+ release from intracellular stores but did not evoke secretion. 2-MeSATP-induced secretion was strongly inhibited by Cd2+ and suppressed by extracellular Ca2+ or Na+ removal. TTX inhibited 2-MeSATP-evoked secretion by ~20%.


CONCLUSIONS
2-MeSATP is a specific P2X purinoceptor agonist and a potent secretagogue in bovine chromaffin cells. Activation of 2-MeSATP-sensitive receptors stimulates Ca2+ influx mainly via voltage-sensitive Ca2+ channels. For the most part, these are activated by the depolarization brought about by Na+ influx across P2X receptor pores.
Tomé
Angelo R
AR
Center for Neurosciences and Cell Biology, University of Coimbra, Coimbra, Portugal. atome@ci.uc.pt <atome@ci.uc.pt>
Castro
Enrique
E
Santos
Rosa M
RM
Rosário
Luís M
LM
D000255:Adenosine Triphosphate / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology; D000311:Adrenal Glands / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002395:Catecholamines / Q000378:metabolism*; D002417:Cattle; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D007425:Intracellular Membranes / Q000378:metabolism; D009994:Osmolar Concentration; D058910:Purinergic P2 Receptor Agonists; D018048:Receptors, Purinergic P2 / Q000502:physiology*; D013873:Thionucleotides / Q000008:administration & dosage / Q000494:pharmacology*; D014544:Uridine Triphosphate / Q000494:pharmacology
D002395:Catecholamines; D058910:Purinergic P2 Receptor Agonists; D018048:Receptors, Purinergic P2; D013873:Thionucleotides; D000255:Adenosine Triphosphate; D002118:Calcium; D014544:Uridine Triphosphate; C008501:2-methylthio-ATP