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Calcium equally increases the internal calcium recirculation fraction before and after beta-blockade in canine left
Insights
Intracoronary calcium administration slightly increased calcium recirculation fraction (RF) after beta-blockade, similar to its effect before blockade. This suggests myocardial cyclic AMP levels do not significantly alter calcium
Area of Science:
- Cardiology
- Physiology
- Pharmacology
Background:
- Beta-blockade impacts cardiac contractility and calcium handling.
- Intracoronary calcium administration is a potential intervention for cardiac dysfunction.
- Understanding calcium recirculation fraction (RF) is crucial for assessing myocardial calcium handling.
Purpose of the Study:
- To investigate the effect of intracoronary calcium administration on calcium recirculation fraction (RF) after beta-blockade.
- To compare the impact of calcium administration before and after beta-blockade on myocardial calcium handling.
- To explore the role of myocardial cyclic AMP-dependent phosphorylation in modulating calcium administration effects.
Main Methods:
- Utilized excised cross-circulated canine hearts for experimental analysis.
- Analyzed the exponential decay component of postextrasystolic potentiation (PESP).
- Measured the time constant (tau(e)) of alternans PESP decay and calculated RF.
Main Results:
- Intracoronary calcium (1.5 mmol/l) enhanced left ventricular contractility index (Emax) 2.5-fold, both before and after beta-blockade.
- Intracoronary calcium administration post-beta-blockade significantly increased tau(e) and consequently RF.
- The observed increase in tau(e) and RF after calcium administration was analogous to findings before beta-blockade.
Conclusions:
- Intracoronary calcium administration influences myocardial calcium handling similarly, irrespective of prior beta-blockade.
- Myocardial cyclic AMP-dependent phosphorylation levels may not significantly alter the effects of intracoronary calcium on myocardial calcium handling.
- The study provides insights into the dynamics of calcium recirculation in the myocardium under different pharmacological conditions.
Abstract:
We studied whether intracoronary Ca administration after beta-blockade would increase the internal Ca recirculation fraction (RF) analogously to the Ca administration before beta-blockade. This was performed in excised cross-circulated canine hearts. We analyzed the exponential decay component of the postextrasystolic potentiation (PESP) following a spontaneous extrasystole. All the PESPs decayed in alternans with atrial pacing at a constant rate. We obtained the time constant (tau(e)) of the monoexponential decay component of the alternans PESP. An increment of intracoronary Ca by 1.5 mmol/l enhanced the left ventricular contractility index Emax (end-systolic maximum elastance) by 2.5 times before and after beta-blockade with propranolol. The intracoronary Ca after beta-blockade slightly but significantly increased tau(e), and hence increased RF calculated from tau(e) by RF = exp(-1/tau(e)). This was analogous to the slightly increased tau(e) and RF with Ca before beta-blockade. We speculate that the myocardial cyclic AMP-dependent phosphorylation level would not significantly alter the effect of intracoronarily administered Ca on myocardial Ca handling, in terms of tau(e) and RF.