Subunit regulation of the human brain alpha 1E calcium channel.

The alpha1 subunit coding for the human brain type E calcium channel (Schneider et al., 1994) was expressed in Xenopus oocytes in the absence, and in combination with auxiliary alpha2delta and beta subunits. alpha1E channels directed with the expression of Ba2+ whole-cell currents that completely inactivated after a 2-sec membrane pulse. Coexpression of alpha1E with alpha2bdelta shifted the peak current by +10 mV but had no significant effect on whole-cell current inactivation. Coexpression of alpha1E with beta2a shifted the peak current relationship by -10 mV, and strongly reduced Ba2+ current inactivation. This slower rate of inactivation explains that a sizable fraction (40 +/- 10%, n = 8) of the Ba2+ current failed to inactivate completely after a 5-sec prepulse. Coinjection with both the cardiac/brain beta2a and the neuronal alpha2bdelta subunits increased by approximately 10-fold whole-cell Ba2+ currents although coinjection with either beta2a or alpha2bdelta alone failed to significantly increase alpha1E peak currents. Coexpression with beta2a and alpha2bdelta yielded Ba2+ currents with inactivation kinetics similar to the beta2a induced currents, indicating that the neuronal alpha2bdelta subunit has little effect on alpha1E inactivation kinetics. The subunit specificity of the changes in current properties were analyzed for all four beta subunit genes. The slower inactivation was unique to alpha1E/beta2a currents. Coexpression with beta1a, beta1b, beta3, and beta4, yielded faster-inactivating Ba2+ currents than currents recorded from the alpha1E subunit alone. Furthermore, alpha1E/alpha2bdelta/beta1a; alpha1E/alpha2bdelta/beta1b; alpha1E/alpha2bdelta/beta3; alpha1E/alpha2bdelta/beta4 channels elicited whole-cell currents with steady-state inactivation curves shifted in the hyperpolarized direction. The beta subunit-induced changes in the properties of alpha1E channel were comparable to modulation effects reported for alpha1C and alpha1A channels with beta3 approximately beta1b > beta1a approximately beta4 >> beta2a inducing fastest to slowest rate of whole-cell inactivation.