title: Subtype-specific reduction of voltage-gated calcium current in medium-sized dorsal root ganglion neurons after painful peripheral nerve injury.
abstract: Sensory neurons express a variety of voltage-gated Ca2+ channel subtypes, but reports differ on their proportionate representation, and the effects of painful nerve injury on each subtype are not established. We compared levels of high-voltage activated currents in medium-sized (30-40 μm) dorsal root ganglion neurons dissociated from control animals and those subjected to spinal nerve ligation, using sequential application of semiselective channel blockers (nisoldipine for L-type, SNX-111 or ω-conotoxin GVIA for N-type, agatoxin IVA or ω-conotoxin MVIIC for P/Q-type, and SNX-482 for a component of R-type) during either square wave depolarizations or action potential waveform voltage commands. Using sequential administration of multiple blockers, proportions of total Ca2+ current attributable to different subtypes and the effect of injury depended on the sequence of blocker administration and type of depolarization command. Overall, however, N-type and L-type currents comprised the dominant components of ICa in sensory neurons under control conditions, and these subtypes showed the greatest loss of current following injury (L-type 26-71% loss, N-type 0-51% loss). Further exploration of N-type current identified by its sensitivity to ω-conotoxin GVIA applied alone showed that injury reduced the peak N-type current during step depolarization by 68% and decreased the total charge entry during action potential waveform stimulation by 44%. Isolation of N-type current by blockade of all other subtypes demonstrated a 50% loss with injury, and also revealed an injury-related rightward shift in the activation curve. Non-stationary noise analyses of N-type current in injured neurons revealed unitary channel current and number of channels that were not different from control, which indicates that injury-induced loss of current is due to a decrease in channel open probability. Our findings suggest that diminished Ca2+ influx through N-type and L-type channels may contribute to sensory neuron dysfunction and pain after nerve injury.
authors.affiliation: Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, WI 53226, USA.
authors.forename: J B
authors.initials: JB
authors.lastname: McCallum
authors.forename: H-E
authors.initials: HE
authors.lastname: Wu
authors.forename: Q
authors.initials: Q
authors.lastname: Tang
authors.forename: W-M
authors.initials: WM
authors.lastname: Kwok
authors.forename: Q H
authors.initials: QH
authors.lastname: Hogan
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D005727:Ganglia, Spinal / Q000187:drug effects / Q000293:injuries / Q000378:metabolism*; D008026:Ligation; D008297:Male; D009437:Neuralgia / Q000378:metabolism* / Q000503:physiopathology; D018408:Patch-Clamp Techniques; D059348:Peripheral Nerve Injuries; D010525:Peripheral Nerves / Q000378:metabolism* / Q000503:physiopathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011984:Sensory Receptor Cells / Q000187:drug effects / Q000378:metabolism*
chemical_list: D002121:Calcium Channel Blockers; D015220:Calcium Channels