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The Journal of Neuroscience, February 15, 2002, 22(4):1256-1265
Serotonergic Raphe Neurons Express TASK Channel Transcripts and a
TASK-Like pH- and Halothane-Sensitive K+ Conductance
Christopher P.
Washburn*,
Jay E.
Sirois*,
Edmund M.
Talley,
Patrice G.
Guyenet, and
Douglas A.
Bayliss
Department of Pharmacology, University of Virginia,
Charlottesville, Virginia 22908
The recently described two-pore-domain K+
channels, TASK-1 and TASK-3, generate currents with a unique set of
properties; specifically, the channels produce instantaneous
open-rectifier (i.e., "leak") K+ currents that
are modulated by extracellular pH and by clinically useful anesthetics.
In this study, we used histochemical and in vitro
electrophysiological approaches to determine that TASK channels are
expressed in serotonergic raphe neurons and to show that they confer a
pH and anesthetic sensitivity to these neurons. By combining in
situ hybridization for TASK-1 or TASK-3 with
immunohistochemical localization of tryptophan hydroxylase, we found
that a majority of serotonergic neurons in both dorsal and caudal raphe
cell groups contain TASK channel transcripts (~70-90%). Whole-cell
voltage-clamp recordings were obtained from raphe cells that responded
to 5-HT in a manner characteristic of serotonergic neurons (i.e., with activation of an inwardly rectifying K+ current). In
those cells, we isolated an endogenous K+
conductance that had properties expected of TASK channel currents; raphe neurons expressed a joint pH- and halothane-sensitive
open-rectifier K+ current. The pH sensitivity of
this current (pK ~7.0) was intermediate between that of TASK-1 and
TASK-3, consistent with functional expression of both channel types.
Together, these data indicate that TASK-1 and TASK-3 are expressed and
functional in serotonergic raphe neurons. The pH-dependent inhibition
of TASK channels in raphe neurons may contribute to ventilatory and
arousal reflexes associated with extracellular acidosis; on the other
hand, activation of raphe neuronal TASK channels by volatile
anesthetics could play a role in their immobilizing and
sedative-hypnotic effects.
Key words:
rat; KCNK; acidosis; anesthetic; hybridization; 5-HT
*
C.P.W. and J.E.S. contributed equally to this work.
Correspondence should be addressed to Douglas A. Bayliss, Department of
Pharmacology, University of Virginia Health System, P.O. Box 800735, Charlottesville, VA 22908-0735. E-mail: dab3y{at}virginia.edu.
Copyright © 2002 Society for Neuroscience 0270-6474/02/2241256-10$05.00/0
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