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 combin ation with the beta(2a) subunit in Xenopus laevis oocytes. 2. The prop erties of ionic and gating currents of alpha(1E) were investigated: io nic currents were measured in 10 mM external Ba2+; gating currents wer e isolated in 2 mM external Co2+. 3. Charge movement preceded channel opening. The charge movement voltage curve (Q(V)) preceded the ionic c onductance voltage dependence (G(V)) by similar to 20 mV. 4. Coexpress ion 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 negat ive potentials. The voltage gap between Q(V) and G(V) curves was reduc ed by the beta(2a) subunit and both curves overlapped at potentials ne ar 0 mV. 5. The coupling efficiency between the charge movement and po re opening was estimated by the ratio between limiting conductance and maximum charge movement (G(max)/Q(max)). Coexpression of the beta(2a) subunit increased the G(max)/Q(max) 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 neurona l alpha(1E) the charge movement is tightly coupled with the pore openi ng and that the beta(2a) subunit coexpression further improves this co upling.