ATP-gated current in dissociated rat nucleus solitarii neurons.
1. The excitatory response of extracellularly applied ATP was investigated in freshly dissociated rat nucleus tractus solitarii neurons under whole-cell configuration using the "concentration-clamp" technique. 2. At a holding potential of -70 mV, 100 microM ATP evoked inward current that was slowly desensitized in the continuous presence of ATP. The ATP-gated current increased in a concentration-dependent manner over the concentration range between 10 microM and 1 mM. The half-maximum concentration was 31 microM and the Hill coefficient was 1.2. 3. The potency of ATP analogues for the purinergic receptor was in the order of ATP = 2-methylthio-ATP much greater than ADP greater than alpha,beta-methylene ATP. Neither adenosine nor AMP evoked any responses. The order was consistent with a P2y receptor subtype. 4. The current-voltage relationship for the 100 microM ATP response showed a clear inward rectification at positive potentials beyond -50 mV. The reversal potential of the ATP-gated current was +13 mV. 5. The time constants of activation and inactivation of the ATP-gated current solution were dependent on the extracellular ATP concentration, and both kinetics became faster at higher ATP concentrations. 6. The ATP-gated current was also elicited in an external solution containing Ca2+ as a permeable cation. The inactivation kinetics in an external solution containing 75 mM Ca2+ were faster than those in an external solution with 150 mM Na+. 7. Calculated relative permeability ratios were PNa/PCs = 1.64 ([Na+]o = 30-150 mM), PCa/PCs = 2.17 ([Ca2+]o = 2 mM). Anions were not measurably permeable in this preparation.
Ueno
S
S
Department of Neurophysiology, Tohoku University School of Medicine, Sendai, Japan.
Harata
N
N
Inoue
K
K
Akaike
N
N
D000255:Adenosine Triphosphate / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002412:Cations / Q000378:metabolism; D004594:Electrophysiology; D015640:Ion Channel Gating; D007700:Kinetics; D008433:Mathematics; D008526:Medulla Oblongata / Q000166:cytology / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D010539:Permeability; D051381:Rats
D002412:Cations; D000255:Adenosine Triphosphate; D002118:Calcium