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Altered contractile function in isoproterenol-induced hypertrophied rat heart
1Department of Biological Sciences, University of Windsor, Ontario, Canada.
Objective:
To study the calcium-dependent mechanisms contributing to altered contractile function in isoproterenol-induced ventricular hypertrophy of the rat heart.
Design:
The force-interval relationship, systemic evaluation of changed contractile force and calcium sensitivity of the myofilaments were investigated using small trabecular muscle from hearts with isoproterenol-induced cardiac hypertrophy.
Methods:
Cardiac hypertrophy was induced by daily subcutaneous injection of isoproterenol for 12 days. The calcium sensitivity of myofilaments was studied using non-ionic detergent (Triton-X-100)-skinned trabeculae. The contractile force was evaluated at various concentrations of extracellular calcium and muscle lengths. The force-interval relationship was used to reflect altered intracellular calcium handling.
Results:
The isoproterenol-induced cardiac hypertrophy was associated with significantly enhanced contractile force at various concentrations of extracellular calcium and muscle lengths. Also, an amplified force-interval relationship in hypertrophied muscle at long rest intervals was found. However, this study revealed no change in calcium sensitivity of myofilaments.
Conclusion:
Altered intracellullar calcium handling contributes to enhanced contractile force in isoproterenol-induced cardiac hypertrophy.