title: ATP-induced inward current in neurons freshly dissociated from the tuberomammillary nucleus.
abstract: 1. Neurons in the tuberomammillary nucleus (TMN), which are considered to be histaminergic, were dissociated and their response to extracellularly applied ATP was investigated in the nystatin-perforated patch recording mode under voltage-clamp condition. 2. ATP induced a sustained inward current that was slowly desensitized at a holding potential of -60 mV. 3. The ATP response increased in a concentration-dependent manner. The half-maximum concentration (EC50) was 44 microM and the Hill coefficient was 1.8. 4. The potency of ATP analogues was in the order of ATP > or = 2-methylthio-ATP >> alpha, beta-methylene ATP > or = ADP. Neither adenosine nor AMP induced any response. The results suggest that the purinergic receptor in TMN neurons is P2y. 5. The current-voltage relationship for the 100 microM ATP showed a significant inward rectification at a potential more positive than -20 mV in an external solution with 150 mM Na+, but a significant rectification current was not observed in an external solution with 150 mM Cs+. The change in the reversal potential of the ATP response (EATP) to a 10-fold change of extracellular Na+ concentration was 56 mV, indicating that the ATP-induced current is highly selective for Na+ over Cl-. 6. The permeability ratio for cations was Na+:Li+:K+:Rb+: Cs+:Ca2+ = 2.16:1.36:1.68:1.54:1:2.55, indicating that the ATP-induced current is passing through the ligand-gated nonselective cation channel. 7. These results suggest that ATP has an excitatory effect on the TMN neurons by opening nonselective cation channels.
authors.affiliation: Department of Neurophysiology, Tohoku University School of Medicine, Sendai, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Furukawa
authors.forename: H
authors.initials: H
authors.lastname: Ishibashi
authors.forename: N
authors.initials: N
authors.lastname: Akaike
mesh_terms: D000255:Adenosine Triphosphate / Q000502:physiology*; D000818:Animals; D015220:Calcium Channels / Q000502:physiology; D018118:Chloride Channels / Q000502:physiology; D006632:Histamine / Q000502:physiology; D008326:Mammillary Bodies / Q000502:physiology*; D009474:Neurons / Q000502:physiology; D051381:Rats; D018048:Receptors, Purinergic P2 / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology*
chemical_list: D015220:Calcium Channels; D018118:Chloride Channels; D018048:Receptors, Purinergic P2; D006632:Histamine; D000255:Adenosine Triphosphate