Figure 4.

Ni²⁺ inhibits Ca²⁺_i responses to ZP3. Ni²⁺ was added either 2 min before (○) or 15 s after ZP3 ( ). Response rates (ΔCa²⁺_i/Δt) were determined as described (Figure 1). (A) Data are means ± SD of observations on 7–22 cells and are fit to the expression I = (100 × IC₅₀)/(IC₅₀ + C), where I is the inhibition of response rates in the presence Ni²⁺ and C and IC₅₀ are the specific Ni²⁺ concentration and the concentration that inhibits Ca²⁺_i response by 50%, respectively. Calculated values of IC₅₀ were 26 μM for Ni²⁺ before ZP3 (black line) and 481 μM for Ni²⁺ after ZP3 (gray line). Letters (a and b) designate points that are illustrated by traces in B. (B) Montage of traces showing sperm treatment with 10 μg/ml ZP3 (●), with 1 mM Ni²⁺ added 15 s after ZP3 ( ), or with Ni²⁺ added 2 min before ZP3 (○).