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Calcium exposure required for full expression of injury in the calcium paradox
Insights
The calcium paradox causes heart injury and protein release. Irreversible heart cell damage occurs within 30 seconds of calcium repletion, even if calcium is removed again.
Area of Science:
- Cardiovascular Physiology
- Cellular Biology
- Biochemistry
Background:
- The calcium paradox describes injury to isolated hearts when calcium is reintroduced after calcium-free perfusion.
- This phenomenon leads to cellular protein release and cell death.
Purpose of the Study:
- To determine the critical time window for calcium repletion that initiates irreversible injury in isolated hearts.
- To investigate the relationship between calcium repletion duration and subsequent protein loss.
Main Methods:
- Isolated rat hearts were perfused with a calcium-free solution, followed by perfusion with a calcium-containing HEPES solution for varying durations (20-30 seconds).
- Hearts were then returned to calcium-free perfusion.
- Protein loss was quantified to assess cellular injury.
Main Results:
- Perfusion with calcium-containing solution for 15 minutes after calcium-free perfusion resulted in significant protein loss (42.7 ± 3.9 mg/g heart).
- A brief 30-second calcium repletion followed by calcium-free perfusion caused similar protein loss.
- Reducing calcium repletion to 20 seconds led to less protein loss (23.9 ± 1.3 mg/g heart), coinciding with the onset of contracture but preceding major ion shifts.
Conclusions:
- The transition to irreversible injury during the calcium paradox occurs rapidly, within approximately 30 seconds of calcium repletion.
- Subsequent removal of extracellular calcium does not prevent the progression of cell death once this critical window is passed.
Abstract:
Isolated hearts repleted with calcium after a short period of perfusion with a calcium-free medium undergo the injury of the calcium paradox and release cellular protein. In the present experiments, 15 min perfusion with a calcium containing HEPES solution subsequent to 10 min calcium-free perfusion resulted in the loss of 42.7 +/- 3.9 mg of protein/g heart. If hearts were repleted with calcium for 30 s only, then returned to calcium-free perfusion, resultant protein loss was the same. When calcium repletion was further decreased to 20 s, 23.9 +/- 1.3 mg/g of protein was lost. This critical period coincided with the onset of contracture but was prior to major ion movements. It is concluded that the transition to irreversible injury occurs within 30 s of calcium repletion and that subsequent removal of extra-cellular calcium does not alter the course of events leading to cell death.