GENESIS: Documentation

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 (τ_m) and inactivation (τ_h) 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 [1]. The whole-cell voltage-clamp study of freshly isolated rat Purkinje cells by [4] (their Figs. 1–3) provided all the data necessary to model activation of T calcium (CaT) current (Fig. 2 B). [3] (their Fig. 4C) have shown a higher threshold of activation for CaT current in Purkinje cells, but [2] reported the same threshold as [4]. The equations for CaT current inactivation were based on a combination of steady-state inactivation data from [3] (their Fig. 5A) and time constant data from [4] (their Fig. 2B), which were almost identical to the data from [3] (their Fig. 5C).

References

[1] AP Fox, MC Nowycky, and RW Tsien. Kinetic and pharmacological properties distinguishing three types of calcium current in chick sensory neurones. Journal of Physiology (Lond.), 394:149–172, 1987.

[2] DL Gruol and CR Deal. Expression of calcium conductances in purkinje neurons in culture. Society for Neuroscience Abstracts, 16:677, 1990.

[3] T Hirano and S Hagiwara. Kinetics and distribution of voltage-gated Ca, Na, and K channels on the somata of rat cerebellar Purkinje cells. Pfluegers Archiv, 413:463–469, 1989.

[4] M Kaneda, M Wakamori, M Ito, and N Akaike. Low-threshold calcium current in isolated Purkinje cell bodies of rat cerebellum. Journal of Neurophysiology, 63:1046–1052, 1990.