Interference Between Two Modulators of N-Type (CaV2.2) Calcium Channel Gating Charge Movement

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The ω-conopeptide Prialt has highlighted N-type calcium channels as an important target for the development of drugs to control neuropathic pain. The ω-conopeptides block N-type channels by plugging the pore, but we recently demonstrated that ω-conotoxin GVIA (ωGVIA) could accelerate N-channel Off-gating charge movement (QOff) and right-shift the Q-V relationship, which our modeling suggested resulted from open state destabilization. R-roscovitine (Rosc) is a purine-based drug that binds to open N-channels to stabilize the open state and slow QOff. Our model predicted that ωGVIA would interfere with the Rosc effect on N-channels, which provided strong test of our conclusions. Gating currents were recorded in 0.2 mM La3+ and 5 mM Mg2+ (LaMg) ± 5 μM ωGVIA from N-channels expressed in HEK 293 cells. As predicted, Rosc-induced effects on QOff were suppressed and shifted to more depolarized voltages. Rosc was able to slow QOff, but the magnitude of that effect was significantly suppressed by ωGVIA, even at strongly depolarized voltages. The QOff time constant (QOffτ) was measured over a range of voltages, and ωGVIA reduced QOffτ at each voltage along with the apparent sensitivity of QOffτ to voltage. As each of these effects was predicted by our modeling, our results provide additional support for the conclusion that ωGVIA affects N-channel gating by destabilizing the open state. The development of novel drugs that isolate this gating effect from the pore-blocking effect could become effective neuropathic pain treatments with a reduced side effect profile.