FUNCTIONAL EXPRESSION AT RAT-BRAIN CLONED ALPHA-1E CALCIUM CHANNELS IN COS-7 CELLS

The properties of the rat brain alpha 1E Ca2+ channel subunit and its modulation by accessory rat brain alpha 2-delta and beta 1b subunits w ere studied by transient transfection in a mammalian cell line in orde r to attempt to reconcile the debate as to whether alpha 1E forms a lo w-voltage-activated (LVA) or high-voltage-activated (HVA) Ca2+ channel and to examine its pharmacology in detail. alpha 1E alone was capable of forming an ion-conducting pore in COS-7 cells. The properties of h eteromultimeric alpha 1E/alpha 2-delta/beta 1b channels were largely d ictated by the presence of the beta 1b subunit, which increased curren t density and tended to produce a hyperpolarizing shift in the voltage dependence of activation and inactivation. alpha 1E/alpha 2-delta/bet a 1b channels did not appear to be regulated by Ca2+-induced inactivat ion. alpha 1E was shown to exhibit a unique pharmacological profile, o mega-Agatoxin IVA blocked the current in a dose-dependent manner with an IC50 Of approximately 50 nM and a maximum inhibition of about 80%, whilst omega-conotoxin MVIIC was without effect. The 1,4-dihydropyridi ne (DHP) antagonist nicardipine (1 mu M) produced an inhibition of 51 +/- 7%, whereas the DHP agonist S-(-)BAY K 8644 was without effect. Ou r findings suggest a re-evaluation of the classification of the alpha 1E Ca2+ channel subunit; we propose that rat brain alpha 1E forms a no vel Ca2+ channel with properties more similar to a subtype of LVA than HVA Ca2+ current.