Omega Conus geographus toxin: A peptide that blocks calcium channels

We previously reported that omega Conus geographus toxin (ωCgTX), blocks evoked-release of transmitter at synapses in frog and attenuates the Ca 2+ component of the action potential of chick dorsal root ganglion neurons. We report here voltage-clamp experiments on cultured chick dorsal root ganglion neurons which demonstrate that ωCgTX produces a persistent block of voltage-gated Ca 2+ currents. Thus, we conclude that ωCgTX inhibits synaptic transmission by blocking Ca 2+ channels in the presynaptic nerve terminal. The toxin had no effect on K + currents; however, in some but not all neurons, ωCgTX reduced Na + currents by 10–25%. These findings suggest that ωCgTX should be useful as a probe to examine synaptic Ca 2+ channels.