Kinetic properties of T-type Ca2+ currents in isolated rat hippocampal CA1 pyramidal neurons.
1. T-type Ca2+ channels producing a transient inward current were studied in pyramidal neurons acutely isolated from the ventral portion of rat hippocampal CA1 region. Membrane currents were recorded by the suction-pipette technique, which allows for internal perfusion under a single-electrode voltage clamp. 2. In all cells superfused with external solution containing 10 mM Ca2+, the T-type Ca2+ current was evoked by step depolarization to potentials more positive than -60 mV from a holding potential of -100 mV and reached a peak in the current-voltage relationship around -30 mV at 20-22 degrees C. 3. Activation and inactivation processes of T-type Ca2+ current were highly potential dependent, and the latter was fitted by a single exponential function. 4. Steady-state inactivation of T-type Ca2+ current could be fitted by a Boltzmann's equation with a slope factor of 6.0 and a half-inactivated voltage of -79 mV. 5. Recovery from inactivation of T-type Ca2+ current was not a single exponent. The major component of recovery (60-90% of total) was voltage sensitive with a time constant of 215 ms at -100 mV. 6. Amplitude of the T-type Ca2+ current depended on the external Ca2+ concentration. The ratio of peak amplitude in the individual current-voltage relationships of Ca2+, Ba2+, and Sr2+ currents passing through T-type Ca2+ channel was 1.0:0.85:1.32. The current kinetics were much the same. 7. All kinetic properties, including activation and inactivation, as well as the amplitude of T-type Ca2+ current, were temperature sensitive with Q10 (temperature coefficient) values of 1.7-2.5.(ABSTRACT TRUNCATED AT 250 WORDS)
Takahashi
K
K
Department of Neurophysiology, Tohoku University School of Medicine, Sendai, Japan.
Ueno
S
S
Akaike
N
N
D000818:Animals; D002118:Calcium / Q000502:physiology; D015220:Calcium Channels / Q000502:physiology*; D004560:Electricity; D006624:Hippocampus / Q000166:cytology / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D011930:Reaction Time; D013696:Temperature
D015220:Calcium Channels; D002118:Calcium