VOLTAGE-DEPENDENT FACILITATION OF CALCIUM CHANNELS IN RAT NEOSTRIATAL NEURONS. Song, Wen-Jie and D. James Surmeier. Dept. of Anatomy and Neurobiology, College of Medicine, University of Tennessee, Memphis, TN 38163.
APStracts 3:0109N, 1996.
SUMMARY AND CONCLUSIONS
1. Voltage-dependent facilitation of Ca 2+ channels was studied in acutely- isolated adult rat neostriatal neurons. Particular attention was paid to the facilitation of L-type channels. 2. In the absence of neuromodulators, the current-voltage relationship for whole cell Ba 2+ currents was enhanced by a pre-pulse to +100 mV. The median enhancement at -20 mV was nearly 60%. The voltage-dependence and kinetics of the processes underlying the facilitation were similar to those reported in other neurons. N-, P-, Q- and L-type currents contributed to the observed facilitation. 3. Voltage-dependent facilitation of L-type currents was studied by subtracting nifedipine- insensitive currents from control currents. Although the kinetics were similar to those of the whole-cell currents, the half-activation voltage for facilitation of L-type currents (V h =-0.6mV, V c =11.8 mV, n=5) was significantly less depolarized than that of the pooled currents (V h =47.3 mV, V c =12.3 mV, n=7). 4. Repetitive depolarization with spike-like waveforms was also able to induce facilitation of L-type currents, arguing that this process was of physiological significance. 5. The L-channel agonist, Bay K 8644 failed to occlude voltage-dependent facilitation of L-type currents, suggesting that facilitation was not simply a consequence of a modal shift in gating like that induced by Bay K 8644 . 6. Combined whole-cell recording and single cell RT- PCR amplification revealed that neostriatal medium spiny neurons expressed detectable levels of either class C or class D L-type channel [alpha] 1 subunit mRNA. Both neurons expressing class C and those expressing class D L- type channels exhibited voltage-dependent facilitation. 

Received 11 October 1996; accepted in final form 16 May 1996.
APS Manuscript Number J674-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 17 June 96