Fig. 5.

Effect of no treatment (TC, no I/R), IR only, or IR + BK_Ca channel antagonist PAX ± SK_Ca channel antagonist NS8593, in 20 isolated guinea pig hearts on respiration (A) and Ca²⁺ retention capacity (CRC) (B) in mitochondria isolated after 20 min reperfusion from groups described in Figs. 1,2. The rate of O₂ consumption (respiration) was measured when substrate was added (state 2), followed by ADP (state 3) and after the added ADP was consumed (state 4); substrates added were pyruvate, succinate, or succinate + rotenone (see also Table 2); state 3/state 4 ratio is defined as the respiratory control index (RCI). Uptake of external Ca²⁺ was assessed (Fura-4 fluorescence) in mitochondria energized under the same 3 substrate conditions; increased number of 20 μM CaCl₂ injections (pulses) = increased CRC. Note hat the decreased RCI with IR only was not different after treatment with the BK_Ca and or SK_Ca antagonists; in contrast, CRC was reduced after treatment with the BK_Ca and or SK_Ca antagonists in the presence of pyruvate or succinate. For each group n = 4; RCI and CRC were measured from same mitochondrial pellet from each heart. * P<0.05.