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Calcium-dependent proteolysis and its inhibition in the ischemic rat myocardium
Insights
In acute myocardial ischemia, calcium-dependent neutral proteinase activity significantly increases. This heightened enzyme activity correlates with reduced inhibitor levels, suggesting a role in heart tissue proteolysis.
Area of Science:
- Biochemistry
- Cardiovascular Physiology
- Enzymology
Background:
- Myocardial ischemia triggers cellular damage.
- Calcium-dependent neutral proteinases are implicated in cellular proteolysis.
Purpose of the Study:
- To investigate the activity of calcium-dependent neutral proteinase and its inhibitor in acutely ischemic rat myocardium.
- To explore the role of enzyme-inhibitor interactions in regulating proteolysis during ischemia.
Main Methods:
- Induction of acute myocardial ischemia via left descending coronary artery ligation in rats.
- Measurement of calcium-dependent neutral proteinase and endogenous inhibitor activity in heart tissue homogenates at various time points post-ligation.
- Comparison with sham-operated and normal control groups.
Main Results:
- Calcium-dependent neutral proteinase activity was significantly elevated in ischemic myocardium, increasing with ischemia duration.
- Enzyme activity was substantially increased in ventricular tissue 20 minutes after ligation.
- The activity of the endogenous inhibitor was significantly reduced in ischemic conditions.
- Sham-operated animals showed a time-dependent increase in enzyme activity.
Conclusions:
- Increased calcium-dependent neutral proteinase activity during acute myocardial ischemia is accompanied by decreased inhibitor levels.
- The interplay between this protease and its inhibitor likely regulates intracellular proteolysis in the ischemic heart.
- Findings suggest a potential mechanism for myocardial damage during ischemic events.
Abstract:
Activity of calcium-dependent neutral proteinase and its specific inhibition was investigated in the acutely ischemic myocardium after ligation of the left descending coronary artery in anaesthetized open chest rats. In experiments where the mean arterial blood pressure could be maintained above 70 mm Hg the hearts were quickly removed 5 to 30 min after ligation and homogenized in ice-cold buffer. The activity of the calcium-dependent neutral proteinase and of its endogenous inhibitor were determined in the 10,000 g supernatant of ventricular and septal tissues. Hearts from normal anaesthetized and sham operated animals left on the respirator for 10, 20 and 30 min, were used as controls. Only traces of proteinase activity could be found in the supernatants obtained from normal controls, while in the sham-operated animals the specific activity of the Ca2+-dependent proteinase increased with time, reaching significantly elevated values after 30 min on the respirator. In the ischemic groups enzyme activity also increased with increasing duration of ischemia and was substantially elevated in the ventricular myocardium 20 min after ligation. The increased calcium-dependent proteinase activity was accompanied by significantly reduced activity of its endogenous inhibitor. The concomitant changes in the activities of the myocardial calcium-dependent neutral protease and its endogenous inhibitor suggest that interaction between the enzyme and its inhibitor play a role in the regulation of intracellular calcium-dependent proteolysis.