Figure 1.

Low and high voltage–activated Ca²⁺ channels have specific Ca²⁺/Ba²⁺ selectivities. (A and B) Representative current traces recorded in oocytes expressing HVA Ca_V1.2, Ca_V2.1, Ca_V2.2, or Ca_V2.3 and α₂-δ + β₂ Ca²⁺ channel subunits (A) or LVA Ca_V3.1, Ca_V3.2, or Ca_V3.3 Ca²⁺ channels (B) using solutions of different Ca²⁺ mole fractions (Ba²⁺/Ca²⁺: 10/0, 9/1, 8/2, 6/4, 4/6, 2/8, and 0/10 mM). Whole-cell currents were recorded during voltage ramps from −80 to +80 mV (A) or from −100 to +60 mV (B) at a speed of 0.4 to 2.6 V/s applied every 15 s. Bars, 100 nA. (C) Normalized current/mole fraction curves obtained from recordings similar to those in A or B by plotting the peak current of the IV curve against the Ca/Ba mole fraction. Note the different ICa/IBa ratios and the presence/absence of AMFE in each case. Left, averaged curves obtained from oocytes expressing Ca_V1.2 (▵), Ca_V2.1 (○), Ca_V2.2 (▿), or Ca_V2.3 (□) HVA VGCC. Right, curves obtained from oocytes expressing Ca_V3.1 (□), Ca_V3.2 (▵) or Ca_V3.3 (○) LVA VGCC.