omega-conotoxin GVIA alters gating charge movement of N-type (CaV2.2) calcium channels.
omega-conotoxin GVIA (omegaCTX) is a specific blocker of N-type calcium (CaV2.2) channels that inhibits neuropathic pain. While the toxin appears to be an open channel blocker, we show that N-channel gating charge movement is modulated. Gating currents were recorded from N-channels expressed along with beta2a and alpha2delta subunits in HEK293 cells in external solutions containing either lanthanum and magnesium (La-Mg) or 5 mM Ca2+ plus omegaCTX (omegaCTX-Ca). A comparison showed that omegaCTX induced a 10-mV right shift in the gating charge versus voltage (Q-V) relationship, smaller off-gating current time constant (tau Q(Off)), a lower tau Q(Off) voltage dependence, and smaller on-gating current (Q(On)) tau. We also examined gating current in La-Mg plus omegaCTX and found no significant difference from that in omegaCTX-Ca; this demonstrates that the modulation was induced by the toxin. A model with strongly reduced open-state occupancy reproduced the omegaCTX effect on gating current and showed that the gating modulation alone would inhibit N-current by 50%. This mechanism of N-channel inhibition could be exploited to develop novel analgesics that induce only a partial block of N-current, which may limit some of the side effects associated with the toxin analgesic currently approved for human use (i.e., Prialt).
Yarotskyy
Viktor
V
Department of Anesthesiology, Penn State College of Medicine, Milton S. Hershey Medical Center, Hershey, PA 17033, USA.
Elmslie
Keith S
KS
D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D020864:Calcium Channels, N-Type / Q000187:drug effects* / Q000235:genetics; D002460:Cell Line; D003198:Computer Simulation; D003627:Data Interpretation, Statistical; D004594:Electrophysiology; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects*; D007700:Kinetics; D007811:Lanthanum / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology; D008959:Models, Neurological; D018408:Patch-Clamp Techniques; D014162:Transfection; D020866:omega-Conotoxin GVIA / Q000494:pharmacology*
C500545:CACNA1B protein, human; D002121:Calcium Channel Blockers; D020864:Calcium Channels, N-Type; D007811:Lanthanum; D020866:omega-Conotoxin GVIA; D008274:Magnesium; D002118:Calcium