Characterization of TTX-resistant persistent Na+ current underlying pacemaker potentials of fish gonadotropin-releasing hormone (GnRH) neurons.
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 tetrodotoxin (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; the cells could thus 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+ currents. 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.
Oka
Y
Y
Zoological Institute, Graduate School of Science, University of Tokyo, Japan.
D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D001683:Biological Clocks / Q000187:drug effects*; D004594:Electrophysiology; D005260:Female; D005399:Fishes / Q000502:physiology*; D007987:Gonadotropin-Releasing Hormone / Q000502:physiology*; D066298:In Vitro Techniques; D008094:Lithium / Q000494:pharmacology; D008297:Male; D008578:Meninges / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D015222:Sodium Channels / Q000187:drug effects*; D013779:Tetrodotoxin / Q000494:pharmacology*
D015222:Sodium Channels; D007987:Gonadotropin-Releasing Hormone; D013779:Tetrodotoxin; D008094:Lithium; D015761:4-Aminopyridine