Key Points
- To determine whether intracellular sodium accumulation drives cell injury in the cardiac calcium paradox and evaluate how membrane potential modulates this process.
- Measured intracellular sodium and calcium ion activities in enzymatically isolated guinea-pig ventricular myocytes using suction-type ion-sensitive microelectrodes under current and voltage clamp.
- Assessed inward currents, sodium accumulation rates, and contraction severity during divalent cation-free depletion and subsequent calcium repletion, incorporating intracellular calcium buffering with BAPTA.
- Inward sodium current through L-type calcium channels, the rate of intracellular sodium accumulation, and subsequent repletion contracture displayed a bell-shaped dependence on membrane potential during calcium depletion.
- Calcium repletion provoked calcium entry quantitatively consistent with a 3 Na+:1 Ca2+ exchange mechanism, and resulting hypercontracture was suppressed dose-dependently by intracellular BAPTA.
- Clamping membrane potential to prevent intracellular sodium elevation during calcium deprivation completely mitigated calcium repletion injury, supporting the intracellular sodium hypothesis.
Structured PICO
PPopulationIsolated guinea-pig ventricular myocytes
IInterventionCalcium depletion and repletion, manipulation of membrane potential, and intracellular sodium buffering with BAPTA
OOutcomeIntracellular activities of Na+ and Ca2+ ions, inward sodium current, and strength of contractionsurrogate
This preclinical study supports the intracellular sodium hypothesis for the origin of the calcium paradox in the heart, demonstrating that preventing the rise in intracellular sodium prevents the effects of calcium repletion.