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Calcium channels in normal and dystrophic hamster cardiac muscle. [3H]nitrendipine binding studies
Insights
Cardiac cell necrosis in dystrophic hamsters is linked to calcium overload. However, studies show no increase in calcium channels, suggesting other mechanisms are responsible for this condition.
Area of Science:
- Cardiology
- Cell Biology
- Biochemistry
Background:
- Progressive cardiac cell necrosis in dystrophic hamsters is potentially linked to intracellular calcium overload.
- Calcium channel antagonists can prevent this necrosis, suggesting a role for calcium regulation.
Purpose of the Study:
- To investigate if an increased number of calcium channels in myopathic cells contributes to excessive calcium influx.
- To quantify the number of [3H]nitrendipine ([3H]NTP) binding sites in cardiac muscle of normal and dystrophic hamsters.
Main Methods:
- Comparison of equilibrium binding studies using [3H]nitrendipine on crude homogenate and partially-purified ventricular muscle preparations.
- Analysis of normal and genetically dystrophic hamster cardiac muscle from 60-day-old animals.
Main Results:
- No significant difference was found in the affinity (KD) or maximum number (Bmax) of [3H]NTP binding sites between normal and dystrophic hamster cardiac muscle.
- For homogenates, KD values were 0.07 ± 0.01 nM (normal) vs. 0.08 ± 0.01 nM (dystrophic), and Bmax values were 62 ± 6 fmol/mg protein (normal) vs. 73 ± 6 fmol/mg protein (dystrophic).
Conclusions:
- A simple increase in the number of calcium channels is unlikely to be the cause of calcium overload in cardiomyopathic hamsters.
- These findings suggest that alternative mechanisms, beyond altered calcium channel density, contribute to calcium dysregulation in this model of cardiac disease.
Abstract:
Progressive cardiac cell necrosis in the dystrophic hamster may be related to intracellular calcium overload, particularly as necrosis is prevented by treatment with calcium channel antagonists. Calcium overload could arise as a consequence of an imbalance in calcium influx, efflux and/or sequestration. The possibility that increased numbers of calcium channels in myopathic cells leads to excessive calcium influx has been studied by assaying the number of [3H]nitrendipine [( 3H]NTP) binding sites in cardiac muscle preparations. Crude homogenate and partially-purified ventricular muscle preparations from 60-day-old normal and genetically dystrophic hamsters were compared in this study. The results of equilibrium binding studies showed that, in both crude and partially-purified membrane preparations, the affinity and the maximum number of [3H]NTP binding sites in normal muscle were not significantly different from those measured in dystrophic muscle. For the homogenate preparation, the KD values were 0.07 +/- 0.01 and 0.08 +/- 0.01 nM for normal and dystrophic tissues, respectively, and the Bmax values were 62 +/- 6 and 73 +/- 6 fmol/mg protein for normal and dystrophic preparations respectively. These data show that a simple increase in the number of [3H]NTP binding sites is unlikely to account for calcium overload in the cardiomyopathic hamster.