Sodium current kinetics in freshly isolated neostriatal neurones of the adult guinea pig.
Neurones of the neostriatum were freshly dispersed from the adult guinea pig brain. A fast, transient inward Na+ current (INa) was analysed using the whole-cell patch-clamp technique. Upon depolarizations, INa developed with a sigmoidal time course, which was described by m3 kinetics. INa showed an activation threshold of about -60 mV, a peak current at -30 to -20 mV, and a reversal of polarity at +60 mV. The steady-state activation (m infinity) curve for INa had a slope factor of about 9 mV for a change in the rate constant by a factor of e) in the range between -50 mV and -20 mV. Conversely, the backward rate constant (beta m) decreased as the membrane was depolarized (about 31 mV for an e-fold change). The steady-state inactivation (h infinity) curve was well expressed by the Boltzmann's equation with a half-inactivation potential of -62 mV and a slope parameter of 6 mV. The time course of INa decay followed a second-order process, whereas the recovery from inactivation was described as a first-order process. The tau h curve showed a bell-shaped configuration with a maximum value at -60 mV. The forward rate constants (alpha h) decreased as the membrane was depolarized (about 17 mV for an e-fold change) in the range between -50 mV and -20 mV. The backward rate constants (beta h) increased as the membrane was depolarized (about 10 mV for an e-fold change). There was a significant overlap between m infinity and h infinity curves, suggesting a steady influx of Na+ (window current).
Ogata
N
N
Department of Pharmacology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Tatebayashi
H
H
D000818:Animals; D003342:Corpus Striatum / Q000502:physiology*; D004553:Electric Conductivity; D005260:Female; D006168:Guinea Pigs; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D015222:Sodium Channels / Q000502:physiology*
D015222:Sodium Channels