The influence exerted by the β_3 subunit on MVIIA ω-conotoxin binding to neuronal N-type calcium channels

摘要

In the present study, two-electrode voltage-clamp techniques have been used to assess the interaction between the MVIIA ω-conotoxin and an isoform of the N-type Ca~(2+) channel α subunit (α_(1B-d)). Cloned α_(1B-d) Ca~(2+) channels were expressed in Xenopus laevis oocytes in the presence and absence of the β_3 subunit. Coexpression of the β_3 subunit significantly shifted the IC_(50) value for MVIIA inhibition of central N-type Ca~(2+) channel current. Analysis of the peak conductance vs. depolarising voltage dependence suggested that the β_3 subunit has no apparent effect on the gating charge which accompanies the closed-open transition of the channels. In stead, coexpression of the β_3 subunit led to an approx. 10 mV shift to more hyperpolarised potentials in the voltage-dependent activation of N-type Ca~(2+) channels. We conclude that MVIIA alters the surface charge on the N-type Ca~(2+) channels and might induce allosteric changes on the structure of the channel, leading to an increase in the dissociation constant of MVIIA binding.