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J Physiol Volume 562, Number 1, 257-269, January 1, 2005 DOI: 10.1113/jphysiol.2004.074211
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Low threshold calcium currents in rat cerebellar Purkinje cell dendritic spines are mediated by T-type calcium channels

Philippe Isope1,2 and Timothy H. Murphy1234

1 Kinsmen Laboratory and Brain Research Centre, Departments of
2 Psychiatry
3 Physiology
4 Graduate Program in Neuroscience, University of British Columbia, Vancouver, British Columbia, Canada

The functional role of low voltage activated (LVA) calcium channels in the cerebellar Purkinje cell dendritic tree is not completely understood. Since the localization of these channels will influence their possible roles in dendritic integration and induction of plasticity, we set out to characterize the LVA calcium current in Purkinje cell dendrites in acute cerebellar slices of young rats. Using a combination of electrophysiological recordings and two-photon laser scanning microscopy, we show that LVA calcium current recorded at the soma can be correlated with voltage-dependent calcium transients in Purkinje cell dendritic spines. Blocking sodium and potassium conductances allowed us to isolate and characterize a fast inactivating inward current activated positive to –55 mV. Activation and steady-state inactivation kinetics, voltage-dependent deactivation kinetics, and pharmacological experiments (using {omega}-agatoxin-IVA, mibefradil and nickel) show that this current is carried by T-type calcium channels. Furthermore, the LVA calcium transient observed in the dendritic spines of the Purkinje cell is well correlated with the current recorded at the soma, suggesting that T-type calcium channels are the main component of the LVA calcium input in spines. The fast rising phase of the calcium transient in spines and the absence of delay between the onset in the spine and the parent dendrite show that T-type calcium channels are present both in spines and dendrites of the Purkinje cell.

(Received 18 August 2004; accepted after revision 22 October 2004; first published online 28 October 2004)
Corresponding author P. Isope: Department of Psychiatry, 4 N1-2255 Wesbrook Mall, Vancouver, BC, Canada V6T 1Z3. Email: isope{at}interchange.ubc.ca




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