(A) Ca²⁺ currents evoked by 100-ms steps from –70 to +40 mV in 10-mV increments applied every 6 s from a V_H of –90 or –50 mV. Shown are representative currents evoked by steps to –60, –40, or +10 mV from a V_H of –90 or –50 mV to reduce Cav3.x channel availability. Current-voltage relationship was constructed from peak current densities (n = 16). (B) Representative currents as in A evoked in the presence of 1 μM (S)-(–)BAYK8644 or 1 μM nifedipine from a V_H of –90 mV. Current-voltage relationships were constructed from peak current densities (n = 8 per group). (C) Ca²⁺ currents evoked by step (100-ms to –40 mV) or tail current (35-ms repolarization to –70 mV following 9-ms step to –40 mV) voltage protocols from a V_H of –90 mV applied every 6 s, in the absence, then presence, of Ni²⁺ in the bath solution from 1 to 100 μM (mean ± SEM). (D) Ni²⁺ inhibition curves of Ca²⁺ channel currents (ICa). Percent inhibition was calculated as measured current relative to maximal current recorded in the absence of Ni²⁺. Datasets were fitted with a logistic equation yielding IC₅₀ 22.5 μM (n = 6) for Ni²⁺ block of Ca²⁺ currents expressed in ZG cells and 9.2 μM (n = 6) for block of recombinant Cav3.2 currents expressed in HEK293 cells.