Characterization of TTX-resistant persistent Na+ current underlying
pacemaker potentials of fish gonadotropin-releasing hormone (GnRH) neurons.
Oka, Yoshitaka
Zoological Institute, Graduate School of Science, University of Tokyo,
Tokyo 113, *Present address; Misaki Marine Biological Station, School of
Science, University of Tokyo, Misaki, Miura, Kanagawa 238-02, Japan.
APStracts 2:0365N, 1995.
SUMMARY AND CONCLUSIONS
1. Endogenous pacemaker activities are important for the putative
neuromodulator functions of the gonadotropin-releasing hormone (GnRH)-
immunoreactive terminal nerve (TN) cells. Previously we have shown by current
clamp analysis that a TTX-resistant persistent Na+ current, INa(slow), plays
an important role in the generation of pacemaker potentials of TN-GnRH cells.
The present study investigates electrophysiological characteristics of
INa(slow) by using the whole-cell patch-clamp technique in in vitro whole-
brain preparation of a small fish brain. 2. TN-GnRH cells lie immediately
beneath the ventral meningeal membrane so that the cells could be exposed and
visualized by gently removing the meningeal membrane. INa(slow) currents were
isolated pharmacologically by blocking K+ currents, Ca2+ currents, and
conventional fast Na+ current. 3. INa(slow) was characterized by resistance to
TTX blockade, dependence on external Na+, slow activation, very slow and
little inactivation, and wide overlap of activation and inactivation curves
near the resting potential. These characteristics are distinct from those of
conventional fast Na+ current, and are relevant for the generation of
persistent inward currents necessary for the pacemaker activity of TN-GnRH
cells.
Received 18 May 1995; accepted in final form 30 November 1995.
APS Manuscript Number J332-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 December 95