Action potential bursts in central snail neurons elicited by d-amphetamine: roles of ionic currents.
The roles of the ionic currents in the firing of potential bursts elicited by d-amphetamine in central snail neurons were studied in the identified RP4 neuron of the African snail, Achatina fulica Ferussac, using the two-electrode voltage-clamp method. Oscillations of membrane potential bursts were elicited by d-amphetamine. The action potential bursts elicited by d-amphetamine decreased following intracellular injection of either EDTA or magnesium, or extracellular application of lanthanum. Voltage-clamped studies revealed that d-amphetamine decreased the fast Na(+), Ca(2+) and transient outward K(+) currents of the RP4 neuron. It also decreased the steady-state K(+) current and elicited a negative slope resistance in the steady-state I-V curve between -50 and -10 mV. The amplitude of negative slope resistance was decreased if either Na(+)-free saline or Co(2+)-substituted Ca(2+)-free saline was perfused. d-Amphetamine did not increase the amplitude of the slowly inactivating Ca(2+) current or the persistent Na(+) currents of RP4 neuron. Tetraethylammonium, a blocker of the delayed outward K(+) current, elicited action potential bursts and negative slope resistance in the RP4 neuron, while 4-aminopyridine, an inhibitor of transient outward K(+) current (I(A)), did not. These results demonstrate that the delayed outward K(+) current and the negative slope resistance in steady-state I-V curve elicited by d-amphetamine may be responsible for the action potential bursts in central snail neurons elicited by d-amphetamine.
Chen
Y H
YH
Department of Pharmacology, College of Medicine, National Taiwan University, Taipei, Taiwan.
Tsai
M C
MC
D015761:4-Aminopyridine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D001030:Apamin / Q000494:pharmacology; D002118:Calcium / Q000502:physiology; D002490:Central Nervous System / Q000166:cytology / Q000502:physiology*; D003913:Dextroamphetamine / Q000494:pharmacology*; D004553:Electric Conductivity; D006706:Homeostasis / Q000187:drug effects; D007477:Ions; D009474:Neurons / Q000187:drug effects* / Q000502:physiology*; D011188:Potassium / Q000502:physiology; D011930:Reaction Time; D012908:Snails / Q000502:physiology*; D012964:Sodium / Q000502:physiology; D019789:Tetraethylammonium / Q000494:pharmacology
D007477:Ions; D001030:Apamin; D019789:Tetraethylammonium; D012964:Sodium; D015761:4-Aminopyridine; D011188:Potassium; D002118:Calcium; D003913:Dextroamphetamine