Inorganic phosphate (P_i) dependence of mitochondrial Ca²⁺ uptake for large or small Ca²⁺ additions. Isolated mitochondria were incubated in 0.1 (A), 1 (B), or 10 (C) mM P_i with 5 mM NaCl, 5 mM G/M, and 1 µM CsA present. Ca²⁺ additions: First Ca²⁺ addition was 15.3 µM, subsequent additions 5.7 µM each (A–C); red line represents mitochondrial membrane potential ΔΨ (D–E). First Ca²⁺ addition 0.2 µM, subsequent 0.011 µM each. The black, red, blue lines represent 0.1, 1.0, and 10.0 mM P_i, respectively. (E) 10 nM Ru360-treated mitochondria.