BKCa currents are enriched in a subpopulation of adult rat cutaneous nociceptive dorsal root ganglion neurons

The biophysical properties and distribution of voltage-dependent, Ca2+ -modulated K+ (BKCa) currents among subpopulations of acutely dissociated DiI-labeled cutaneous sensory neurons from the adult rat were characterized with whole-cell patch-clamp techniques. BKCa currents were isolated from total K+ current with iberiotoxin, charybdotoxin or paxilline. There was considerable variability in biophysical properties of BKCa currents. There was also variability in the distribution of BKCa current among subpopulations of cutaneous dorsal root ganglia (DRG) neurons. While present in each of the subpopulations defined by cell body size, IB4 binding or capsaicin sensitivity, BKCa current was present in the vast majority (> 90%) of small-diameter IB4+ neurons, but was present in only a minority of neurons in subpopulations defined by other criteria (i.e. small-diameter IB4-). Current-clamp analysis indicated that in IB4+ neurons, BKCa currents contribute to the repolarization of the action potential and adaptation in response to sustained membrane depolarization, while playing little role in the determination of action potential threshold. Reverse transcriptase-polymerase chain reaction analysis of mRNA collected from whole DRG revealed the presence of multiple splice variants of the BKCa channel alpha-subunit, rslo and all four of the accessory beta-subunits, suggesting that heterogeneity in the biophysical and pharmacological properties of BKCa current in cutaneous neurons reflects, at least in part, the differential distribution of splice variants and/or beta-subunits. Because even a small decrease in BKCa current appears to have a dramatic influence on excitability, modulation of this current may contribute to sensitization of nociceptive afferents observed following tissue injury.