pH dependence of facilitation by neurotransmitters and divalent cations of P2X2 purinoceptor/channels.
The pH dependence of the facilitation by dopamine (10 microM), 5-hydroxytryptamine (10 microM), adenosine (1 and 100 microM), Zn2+ (10 microM) and Cd2+ (1 mM) of P2X2 purinoceptor/channels was tested by expressing these channels in Xenopus oocytes. In a pH range between 6.0 and 8.5, concentration-response curves for an inward current activated by ATP were shifted toward a lower concentration range at a more acidic pH, indicating that the sensitivity to ATP is pH-dependent. Comparison of the effects of the neurotransmitters and the divalent cations on the ATP-activated current was made using a concentration of ATP which activated 40-50% of the maximal current at each pH value. The current facilitation by dopamine was obvious at pH 7.1 and 7.7, but was not observed at pH 8.5. At pH 6.0, the current was inhibited upon first trials of dopamine, but it was facilitated upon second trials. With 5-hydroxytryptamine and adenosine, the current facilitation was most remarkable at pH 6.0, less remarkable at pH 7.1 and 7.7, and the facilitation was almost abolished at pH 8.5. On the other hand, the current facilitation by Zn2+ and Cd2+ was more remarkable at alkaline pH values (7.7 and 8.5), and the facilitation was almost abolished at pH 6.0. The results suggest that the facilitation of P2X2 purinoceptors depends on pH, and the pH dependence was different between the neurotransmitters and the divalent cations.
Nakazawa
K
K
Division of Pharmacology, National Institute of Health Sciences, Setagaya, Tokyo, Japan.
Liu
M
M
Inoue
K
K
Ohno
Y
Y
D000241:Adenosine / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002104:Cadmium / Q000494:pharmacology; D002413:Cations, Divalent / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007473:Ion Channels / Q000096:biosynthesis / Q000187:drug effects*; D008564:Membrane Potentials / Q000187:drug effects; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D009865:Oocytes; D018408:Patch-Clamp Techniques; D018048:Receptors, Purinergic P2 / Q000096:biosynthesis / Q000187:drug effects*; D058476:Receptors, Purinergic P2X2; D011994:Recombinant Proteins / Q000096:biosynthesis; D012701:Serotonin / Q000494:pharmacology; D014982:Xenopus laevis; D015032:Zinc / Q000494:pharmacology
D002413:Cations, Divalent; D007473:Ion Channels; D018377:Neurotransmitter Agents; D018048:Receptors, Purinergic P2; D058476:Receptors, Purinergic P2X2; D011994:Recombinant Proteins; D002104:Cadmium; D012701:Serotonin; D000255:Adenosine Triphosphate; D015032:Zinc; D000241:Adenosine