Morphologically identified cutaneous afferent DRG neurons express three different potassium currents in varying proportions.
Outward K+ currents were recorded using a whole cell patch-clamp configuration, 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 16-24 h after dissociation from cells between 39 and 49 mm 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 recorded routinely during 300-ms depolarizing test pulses increasing in 10-mV steps from -40 to +50 mV; the currents were preceded by a 500-ms conditioning prepulse of either -120 or -40 mV. Coexpression 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 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 mM 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). On the basis of the relative distribution of K+ currents neurons could be separated into three distinct categories: fast inactivating current (IA), slow inactivating current (ID), and sustained current (IK); only IA and IK; and slow inactivating current 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).
Everill
B
B
Department of Neurology, Yale University School of Medicine, New Haven 06510, USA.
Rizzo
M A
MA
Kocsis
J D
JD
D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D001369:Axons / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004546:Elapid Venoms / Q000494:pharmacology; D005727:Ganglia, Spinal / Q000166:cytology / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D009186:Myelin Sheath / Q000502:physiology; D009475:Neurons, Afferent / Q000502:physiology* / Q000648:ultrastructure; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012867:Skin / Q000294:innervation*; D019789:Tetraethylammonium / Q000494:pharmacology; D014110:Touch / Q000502:physiology
D002121:Calcium Channel Blockers; D004546:Elapid Venoms; D015221:Potassium Channels; D019789:Tetraethylammonium; C020273:dendrotoxin; D015761:4-Aminopyridine