Coupling between charge movement and pore opening in vertebrate neuronal alpha 1E calcium channels

1. Neuronal alpha 1E Ca2+ channels were expressed alone and in combination with the beta 2a subunit in Xenopus laevis oocytes. 2. The properties of ionic and gating currents of alpha 1E were investigated: ionic currents were measured in 10 mM external Ba2+; gating currents were isolated in 2 mM external Co2+. 3. Charge movement preceded channel opening. The charge movement voltage curve (Q(V)) preceded the ionic conductance voltage dependence (G(V)) by approximately 20 mV. 4. Coexpression of alpha 1E with the beta 2a subunit did not modify the voltage dependence of charge movement but shifted the G(V) curve to more negative potentials. The voltage gap between Q(V) and G(V) curves was reduced by the beta 2a subunit and both curves overlapped at potentials near 0 mV. 5. The coupling efficiency between the charge movement and pore opening was estimated by the ration between limiting conductance and maximum charge movement (Gmax/Qmax). Coexpression of the beta 2a subunit increased the Gmax/Qmax ratio from 9.2 x 10(5) +/- 1.4 x 10(5) to 21.9 x 10(5) +/- 2.8 X 10(5) S C-1 for alpha 1E and alpha 1E + beta 2a, respectively. 6. We conclude that in the neuronal alpha 1E the charge movement is tightly coupled with the pore opening and that the beta 2a subunit coexpression further improves this coupling.