IIV relations at different concentrations of Ca²⁺_o (A and B) and Ba²⁺_o (C and D). Values are from 5, 8, 5, 7, 4, and 3 cells in Ca²⁺_o, and 3, 5, 7, 6, 4, and 3 cells in Ba²⁺_o (respectively, 100 nM, 10 μM, 0.1 mM, 0.5 mM, 8 mM, and 110 mM). Control values at 2 mM Ca²⁺_o or Ba²⁺_o are averaged from all these cells (32 in Ca²⁺_o, 28 in Ba²⁺_o). In each cell, the control value was the average of measurements before and after the test solution, to correct for rundown. Values were normalized for each cell as described in Materials and methods. 3–5,⁴⁵ are based on this same dataset.