Journal of Neurophysiology, Vol 63, Issue 5 1046-1051, Copyright © 1990 by APS

ARTICLES

Low-threshold calcium current in isolated Purkinje cell bodies of rat cerebellum

M. Kaneda, M. Wakamori, C. Ito and N. Akaike
Department of Neurophysiology, Tohoku University School of Medicine, Sendai, Japan.

1. The low- and high-threshold Ca2+ currents were observed in Purkinje cell bodies isolated from the cerebellum of newborn (2 wk old) and adult (8 wk old) rats under whole-cell clamp. A transient Ca2+ current (low-threshold or "T-type" ICa) was elicited by depolarizing step pulses to -60 mV or more positive potentials from a holding potential (VH) of -100 mV. In cells dissociated from newborn rats, a long-lasting Ca2+ current (high-threshold or "L-type" ICa) was also elicited by depolarizing command pulses beyond -30 mV. 2. The low-threshold ICa was resistant to the "washout" effect during the internal perfusion, whereas the high-threshold ICa faded gradually with time during the continuous internal perfusion. 3. In the current-voltage (I-V) relationship, the low-threshold ICa had a threshold potential around -60 mV and reached the maximum inward current around -20 mV. The activation and inactivation kinetics of the current depended on membrane potential: for a test-potential change from -60 to +40 mV, the time to peak of the current (activation) decreased from 31.9 to 5.0 ms, and the time constant of current decay (inactivation) decreased from 78.5 to 22.9 ms. 4. Steady-state inactivation of low-threshold ICa was membrane-potential dependent, and the inactivation of the 50% level was -79 mV. Recovery time constant from steady-state inactivation varied depending on the membrane potential. The time constants were 3.3 and 2.5 s at VHs of -100 and -120 mV, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

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