De Schutter: Purkinje Cell Model
|Figure 1: ||Activation and inactivation properties of the T-type calcium
current (CaT, —) in the model. Seady-state activation and inactivation vs.
voltage are plotted at the left, the time constants of activation (τm) and
inactivation (τh) vs. voltage in the middle (Note: Semilogarithmic scale), and
a simulation of representative voltage-clamp currents at the right, obtained
from a spherical cell and assuming a complete block of all other channels.
They simulate steps from a holding potential of -110 to -70 mV up to 0 mV
in 10 mV increments. The voltage-clamp current amplitude has been scaled
arbitrarily because we mainly wanted to demonstrate the current kinetics.|
T-Type Calcium Current
Several groups have reported the presence of a low-threshold, inactivating Ca2+
channel in the Purkinje cell [2, 3, 4] comparable to the T channel in other
neurons . The whole-cell voltage-clamp study of freshly isolated rat
Purkinje cells by  (their Figs. 1–3) provided all the data necessary
to model activation of T calcium (CaT) current (Fig. 2 B).  (their
Fig. 4C) have shown a higher threshold of activation for CaT current in
Purkinje cells, but  reported the same threshold as . The equations for
CaT current inactivation were based on a combination of steady-state
inactivation data from  (their Fig. 5A) and time constant data from  (their
Fig. 2B), which were almost identical to the data from  (their Fig.
 AP Fox, MC Nowycky, and RW Tsien. Kinetic and pharmacological
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 DL Gruol and CR Deal. Expression of calcium conductances in
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 T Hirano and S Hagiwara. Kinetics and distribution of voltage-gated
Ca, Na, and K channels on the somata of rat cerebellar Purkinje cells.
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 M Kaneda, M Wakamori, M Ito, and N Akaike. Low-threshold
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