Figure 1. The [Ca²⁺]_ER-response relation for the CRAC channel.

Simultaneous measurements of [Ca²⁺]_ER and I_CRAC in individual Jurkat T cells. a, Non-stationary measurements of I_CRAC and [Ca²⁺]_ER. Store depletion with 20 μM CPA induces an increase in I_CRAC (top) that follows a decrease in [Ca²⁺]_ER (middle) monitored with YC4.2er. The I-V relationship shows the inward rectification typical of I_CRAC (bottom). In this cell, a small inward current through outwardly-rectifying Cl⁻ channels is also present initially but disappears before I_CRAC is induced. b, Recordings of I_CRAC (top) and [Ca²⁺]_ER (middle) under steady-state conditions. Each cell was treated with the indicated CPA concentration for 8–15 min prior to recording, and CPA was maintained throughout the experiment. I-V relations are typical for I_CRAC (bottom). c, Steady-state I_CRAC and [Ca²⁺]_ER are plotted for 40 cells after treatment with 0.5–20 μM CPA. A fit of the Hill equation with a K_1/2 of 169 μM and Hill coefficient of 4.2 is superimposed on the data. Squares: mean ± s.e.m. of 3–12 cells. Circles: single cells (see Supplementary Information).