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Effect of prolonged hypothermic ischaemia on myocardial sarcoplasmic reticular calcium transport
K Fukumoto1, H Takenaka, Y Koga
1Second Department of Surgery, Miyazaki Medical College, Japan.
Insights
Hypothermia preserves myocardial sarcoplasmic reticulum function during ischemia for up to 3 hours. Beyond this, calcium uptake is impaired, and Ca-ATPase activity decreases, suggesting uncoupling and reduced pump units.
Area of Science:
- Cardiology
- Biochemistry
- Cellular Physiology
Background:
- Myocardial ischemia leads to impaired calcium regulation.
- Sarcoplasmic reticulum (SR) dysfunction contributes to cardiac damage during ischemia.
- Understanding SR response to hypothermia is crucial for preserving heart function.
Purpose of the Study:
- To evaluate the impact of hypothermia on myocardial sarcoplasmic reticulum (SR) function.
- To compare the effects of hypothermic vs. normothermic ischemia on SR calcium handling.
- To determine the duration of hypothermic protection for SR during prolonged ischemia.
Main Methods:
- Isolated rabbit hearts subjected to varying durations of hypothermic (4°C) or normothermic (37°C) ischemia.
- Measurement of calcium uptake and calcium-dependent ATPase (Ca-ATPase) activity in SR vesicles.
- Analysis of SR protein composition using SDS-PAGE.
Main Results:
- Normothermic ischemia markedly inhibited Ca-ATPase activity and calcium uptake.
- Hypothermic ischemia showed only slight depression of calcium uptake at 3 hours.
- Significant depression of calcium uptake occurred after 6 hours of hypothermic ischemia, with reduced Ca-ATPase activity at 12 hours.
Conclusions:
- Hypothermia preserves myocardial SR function for up to 3 hours of ischemia.
- Impaired calcium uptake after 6 hours of hypothermia is likely due to uncoupling of calcium transport from ATP hydrolysis.
- Reduced Ca-ATPase activity at 12 hours suggests a decrease in functional calcium pump units.
Study Objective:
The aim of the study was to assess the effects of hypothermia on sarcoplasmic reticulum in myocardium subjected to prolonged ischaemia.
Design:
Calcium regulatory activity of myocardial sarcoplasmic reticulum was measured in hearts subjected to various periods of hypothermic ischaemia in comparison with hearts subjected to normothermic ischaemia.
Subjects:
Hearts (n = 5-9 per experiment) were obtained from male New Zealand white rabbits, 2.0-2.8 kg weight.
Measurements And Results:
Calcium uptake and calcium dependent ATPase activity were measured in isolated sarcoplasmic reticulum vesicles after hypothermic ischaemia was produced by immersing hearts in saline at 4 degrees C for 3, 6, or 12 h. Normothermic hearts were immersed for 3 h at 37 degrees C. Calcium uptake and calcium dependent ATPase (Ca-ATPase) activity were markedly inhibited by normothermic ischaemia. In hypothermic ischaemia, calcium uptake was only slightly depressed after 3 h, though longer periods of ischaemia resulted in significant depression of uptake. Ca-ATPase activity was unaffected after 6 h of hypothermic ischaemia. The ratio of calcium uptake to Ca-ATPase activity decreased after 3 h of hypothermic ischaemia. The phosphoenzyme concentration in sarcoplasmic reticulum was unaffected up to 6 h. The ratio of Ca-ATPase activity to phosphoenzyme concentration was not significantly altered until 12 h. Protein composition, examined by SDS-polyacrylamide gel electrophoresis, showed a decrease in 100,000 dalton polypeptide in normothermic ischaemia and after 12 h of hypothermic ischaemia.
Conclusions:
These results suggest that the depression of calcium uptake activity after 6 h of hypothermic ischaemia is likely to be due to uncoupling of calcium transport from ATP hydrolysis. Depressed Ca-ATPase activity at 12 h can be attributed to a reduction in the number of active calcium pump units. Hypothermia preserves function of myocardial sarcoplasmic reticulum during ischaemia for up to 3 h.