Capsaicin-Induced Currents With Distinct Desensitization and Ca ++
Dependence in Rat Trigeminal Ganglion Cells.
Liu, L. and S.A. Simon.
From.
APStracts 2:0314N, 1995.
SUMMARY AND CONCLUSIONS
1. Whole cell patch-clamp records from cultured rat trigeminal ganglion cells
having soma diameters ranging from 20-50 [mu]m revealed that capsaicin
activated two inward currents and an outward current. At -60 mV, the inward
currents could be distinguished by their different peak times that were 4 .2
+/- 3.1 and 41.4 +/- 16.4 seconds. 2. Cells with the smallest soma diameters
had the largest current densities. 3. The more rapidly-activating current had
a linear current-voltage relation and a reversal potential near 0 mV. 4. The
more slowly-activating current is not a Ca ++ activated Cl - current. 5. The
peak of the rapid current (Ip)-capsaicin concentration (C) relationship was
characterized by Ip/Ip max = (1 + (C/Kd) n ) -1 where n = 1.2 and K [delta] =
0.68 [mu]M. 6. The rapidly activating current was heterogeneous in regard both
to its rate of activation and extent of desensitization. In cells bathed in
buffer containing calcium, and held at -60 mV, most of the capsaicin-activated
currents desensitized. Removal of extracellular Ca ++ could reduce, eliminate,
or have no effect on desensitization. 7. At positive holding potentials the
currents very slowly desensitized, even in the presence of Ca ++ . 8. Repeated
30 second applications of 1 [mu]M capsaicin separated by 0.5, 2.5 and 5.5
minutes all induced tachyphylaxis. Tachyphylaxis decreased exponentially until
the current remained approximately constant. Decreasing the time between
capsaicin applications increased the extent of tachyphylaxis, whereas
elimination of extracellular Ca ++ markedly reduced tachyphylaxis.
Received 7 August 1995; accepted in final form 20 October 1995.
APS Manuscript Number J512-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 November 95