Effects of P_i, (black), arsenate (As_i, blue), or vanadate (V_i, red) anions on the regulation of mitochondrial Ca²⁺. The buffer solution contained 2 mM P_i, As_i, or V_i in the presence of 1 µM of CsA. (A–E) Large Ca²⁺ additions (first Ca²⁺ addition was 15.3 µM, subsequent additions 5.7 µM each) were made until mitochondrial PTP opening occurred, as indicated by ΔΨ_m collapse (C), swelling (D), and uncontrolled Ca²⁺ efflux (A). (F–J) Smaller Ca²⁺ additions (first Ca²⁺ addition 0.2 µM, subsequent 0.011 µM each) evoked similar [Ca²⁺]_mito responses without significantly disrupting ΔΨ_m or activating PTP.