THE ALPHA(1E) CALCIUM-CHANNEL EXHIBITS PERMEATION PROPERTIES SIMILAR TO LOW-VOLTAGE-ACTIVATED CALCIUM CHANNELS

The physiological and pharmacological properties of the ct,, calcium ( Ca) channel subtype do not exactly match any of the established catego ries described for native neuronal Ca currents. Many of the key diagno stic features used to assign cloned Ca channels to their native counte rparts, however, are dependent on a number of factors, including cellu lar environment, beta subunit coexpression, and modulation by second m essengers and G-proteins. Here, by examining the intrinsic pore charac teristics of a family of transiently expressed neuronal Ca channels, w e demonstrate that the permeation properties of alpha(1E) closely rese mble those described for a subset of low-threshold Ca channels. The al pha(1A) (P-/Q-type), alpha(1B) (N-type), and alpha(1C) (L-type) high-t hreshold Ca channels all exhibit larger whole-cell currents with bariu m (Ba) as the charge carrier as compared with Ca or strontium (Sr). In contrast, macroscopic alpha(1E) currents are largest in Sr, followed by Ca and then Ba. The unique permeation properties of alpha(1E) are m aintained at the single-channel level, are independent of the nature o f the expression system, and are not affected by coexpression of alpha (2) and beta subunits. Overall, the permeation characteristics of alph a(1E) are distinct from those described for R-type currents and share some similarities with native low-threshold Ca channels.