The biophysical properties and distribution of voltage-dependent, Ca 2+ -modulated K + (BK Ca ) currents among subpopulations of acutely dissociated DiI labeled cutaneous sensory neurons from the adult rat were characterized with whole cell patch clamp techniques. BK Ca currents were isolated from total K + current with iberiotoxin, charybdotoxin, or paxilline. There was considerable variability in biophysical properties of BK Ca currents. There was also variability in the distribution of BK Ca current among subpopulations of cutaneous DRG neurons. While present in each of the subpopulations defined by cell body size, IB4 binding or capsaicin sensitivity, BK Ca current was present in 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, BK Ca 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. RT-PCR analysis of mRNA collected from whole DRG revealed the presence of multiple splice variants of the BK Ca channel α-subunit, rslo and all 4 of the accessory β subunits, suggesting that heterogeneity in the biophysical and pharmacological properties of BK Ca current in cutaneous neurons, reflects, at least in part, the differential distribution of splice variants and/or β subunits. Because even a small decrease in BK Ca current appears to have a dramatic influence on excitability, modulation of this current may contribute to sensitization of nociceptive afferents observed following tissue injury.

No abstract

No abstract