Key Points
- To determine whether acidosis and free radicals interact to cause excitation-contraction uncoupling and sarcoplasmic reticulum dysfunction in the ischemic myocardium.
- Isolated cardiac sarcoplasmic reticulum (SR) and whole heart homogenates from canine left ventricle.
- Measured calcium uptake velocity and Ca2+-stimulated Mg2+-dependent ATPase activity across varying pH levels (7.0 vs. 6.4) with or without exogenous free radicals generated by xanthine and xanthine oxidase.
- Evaluated the reversibility of calcium transport defects using superoxide dismutase (SOD) and the hydroxyl radical scavenger mannitol across varying preincubation times.
- Acidosis (pH 6.4) reduced calcium uptake from 0.95 ± 0.02 to 0.50 ± 0.02 μmol Ca2+·mg protein−1·min−1 (p < 0.01) and decreased the coupling ratio from 0.87 ± 0.06 to 0.51 ± 0.05 without affecting ATPase activity.
- At pH 7.0, free radicals reduced calcium uptake (0.15 ± 0.02 vs. 0.95 ± 0.02) and ATPase activity (0.30 ± 0.01 vs. 1.05 ± 0.02 μmol Pi·mg protein−1·min−1; p < 0.01), both of which were fully reversed by SOD.
- At pH 6.4, free radicals lowered calcium uptake to 0.11 ± 0.01 μmol Ca2+·mg protein−1·min−1 (coupling ratio 0.13), requiring both SOD and 20 mM mannitol to normalize transport.
Structured PICO
PPopulationCardiac sarcoplasmic reticulum (SR) isolated from the wall of canine left ventricle and whole heart homogenate
IInterventionExposure to acidosis (pH 6.4) and exogenous free radicals generated from the xanthine-xanthine oxidase system
CComparatorNormal pH (7.0) and absence of exogenous free radicals
OOutcomeCalcium uptake velocity and Ca2+-stimulated Mg2+-dependent ATPase activitysurrogate
Acidosis and free radical generation (specifically hydroxyl radicals) uncouple calcium transport from ATP hydrolysis in canine cardiac sarcoplasmic reticulum, suggesting a mechanism for the transition from reversible to irreversible myocardial ischemia.