A P2 purinoceptor activated by ADP in rat medullar neurons.
ADP evoked outwardly rectifying potassium currents with a latency of 0.6 s in cultured rat medullar neurons. Purinoceptor agonists, such as 2-methylthio ATP (2-MeSATP), ATP, AMP, alpha,beta-methylene ATP (alpha,beta-MeATP), and UTP, produced similar outward currents with the order of their potencies for current amplitudes: 2-MeSATP > ADP > ATP > or = alpha,beta-MeATP > or = AMP > UTP. This order corresponds to that for a subtype of P2Y purinoceptors. ADP-evoked currents were fully blocked by a broad G-protein inhibitor, guanosine-5'-O-(2-thiodiphosphate) (GDP beta S), whereas a G(i)/G(o)-protein inhibitor, pertussis toxin (PTX) had no effect. The currents were not affected by a phospholipase C (PLC) inhibitor, neomycin. Furthermore, a selective protein kinase C inhibitor, GF109203X or a selective cAMP-dependent protein kinase inhibitor, H-89 showed no effect on the currents. These results suggest that ADP activates the potassium channel via a P2Y purinoceptor linked to a PTX-insensitive G-protein and its channel regulation may be due to a direct action of the G-protein beta gamma subunits regardless of second messenger signaling cascades. Additionally, ADP enhanced intracellular free Ca2+ concentration ([Ca2+]i) both in the presence and absence of extracellular calcium, and this [Ca2+]i increase was not inhibited by neomycin. This provides an additional evidence that ADP binds to a subtype of P2Y purinoceptors, which is not involved in PLC stimulation.
Ikeuchi
Y
Y
Department of Physiology, Kobe University School of Medicine, Japan.
Nishizaki
T
T
Okada
Y
Y
D000244:Adenosine Diphosphate / Q000494:pharmacology*; D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism*; D001711:Biotransformation / Q000187:drug effects; D002478:Cells, Cultured; D016257:Fura-2; D019204:GTP-Binding Proteins / Q000378:metabolism; D008526:Medulla Oblongata / Q000166:cytology / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D051381:Rats; D018048:Receptors, Purinergic P2 / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects
D015221:Potassium Channels; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2; D000244:Adenosine Diphosphate; D019204:GTP-Binding Proteins; D016257:Fura-2