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Abstract
Small (SK) and intermediate (IK) conductance calcium-activated potassium channels
are candidate ion channels for the regulation of excitability in nociceptive neurones.
We have used unique peptide-directed antisera to describe the immunocytochemical distribution
of the known isoforms of these ion channels in dorsal root ganglia (DRG) and spinal
cord of the rat. These investigations sought to characterize further the phenotype
and hence possible functions of nociceptive neurone subpopulations in the rat. In
addition, using Western blotting, we sought to determine the level of protein expression
of SK and IK channels in sensory nervous tissues following induction of inflammation
(Freund's Complete Adjuvant (FCA) arthritis model) or nerve injury (chronic constriction
injury model). We show that SK1, SK2, SK3 and IK1 are all expressed in DRG and spinal
cord. Morphometric analysis revealed that SK1, SK2 and IK1 were preferentially localized
to neurones having cell bodies <1000 microm2 (putative nociceptors) in DRG. Dual labeling
immunocytochemistry showed that these ion channels co-localize with both CGRP and
IB4, known markers of nociceptor sub-populations. SK2 was localized almost exclusively
in the superficial laminae of the spinal cord dorsal horn, the region in which many
sensory afferents terminate; the distribution of SK1 and IK1 was more widespread in
spinal cord, although some preferential labeling within the dorsal horn was observed
in the case of IK1. Here we show evidence for a distinctive pattern of expression
for certain members of the calcium-activated potassium channel family in the rat DRG.