Morphologically identified cutaneous afferent DRG neurons express three different potassium currents in varying proportions . Brian Everill, Marco A. Rizzo and Jeffery D. Kocsis. Department of Neurology, Yale University School of Medicine, New Haven, CT 06510 (USA) and Neuroscience Research Center, Department of Veterans Affairs Medical Center, West Haven, CT 06516 (USA)..
APStracts 4:338N, 1997.
ABSTRACT
Outward K+ currents were recorded using whole cell patch-clamp from acutely dissociated adult rat cutaneous afferent dorsal root ganglion (DRG) neurons (L4 and L5) identified by retrograde labeling with Fluoro-gold. Recordings were obtained 16 to 24 hours after dissociation from cells between 39 to 49 æm in diameter with minimal processes. These cells represent medium-sized DRG neurons relative to the entire population, but are large cutaneous afferent neurons giving rise to myelinated axons. Voltage-activated K+ currents were routinely recorded during 300 ms depolarizing test pulses increasing in 10 mV steps from -40 mV to +50 mV which were preceded by a 500 msec conditioning prepulse of either -120 mV or -40 mV. Co-expression of at least three components of K+ current was revealed. Separation of these components was achieved on the basis of sensitivities to the K+ channel blockers, 4- aminopyridine (4-AP) and dendrotoxin (DTx), and by the current responses to variation in conditioning voltage. Changing extracellular K+ concentration from 3 mM to 40 mM resulted in a shift to the right of the I-V curve commensurate with K+ being the principal charge carrier. Presentation of 100 æM 4-AP revealed a rapidly activating K+ current sensitive to low concentrations of 4-AP. High concentrations of 4-AP (6 mM) extinguished all inactivating current, leaving almost pure sustained current (IK). Based on the relative distribution of K+ currents neurons could be separated into three distinct categories: a) fast inactivating current (IA), slow inactivating current (ID), and sustained current (IK); b) only IA and IK; and c) slow inactivating and IK. However, IK was always the dominant outward current component. These results indicate that considerable variation in K+ currents is present not only in the entire population of DRG neurons, as previously reported, but even within a restricted size and functional group (large cutaneous afferent neurons). 

Received 29 May 1997; accepted in final form 21 November 1997.
APS Manuscript Number J449-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 12 December 1997