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Subcellular calcium content in cardiomyopathic hamster hearts in vivo: an electron probe study
M Bond1, A R Jaraki, C H Disch
1Department of Heart and Hypertension, Research Institute of the Cleveland Clinic Foundation, OH 44195-5069.
Insights
Myopathic hamster hearts show varied cellular calcium levels, not a generalized overload. Localized calcium increases occur only at necrotic sites, challenging previous theories on heart failure pathogenesis.
Area of Science:
- Cardiovascular Research
- Cellular Biology
- Pathophysiology
Background:
- Abnormal cellular calcium regulation is implicated in Syrian cardiomyopathic hamster heart failure.
- An alternative hypothesis suggests coronary vasospasm leading to necrosis as the primary issue.
Purpose of the Study:
- To investigate whether myopathic hamster hearts exhibit generalized myocytic calcium elevation.
- To differentiate between generalized calcium overload and localized increases at necrotic sites.
Main Methods:
- Electron probe microanalysis of cryosections from myopathic and control hamster hearts (50- and 96-day-old).
- Measurement of total ventricular calcium content using atomic absorption spectrophotometry.
- In vivo rapid freezing to preserve cellular calcium distribution.
Main Results:
- No significant differences in subcellular calcium levels were found between myopathic and control hearts.
- Localized calcium elevations were observed exclusively at sites of necrotic foci.
- Total heart calcium content was significantly higher in myopathic hamsters (13-50 times controls).
Conclusions:
- The study does not support a generalized cellular calcium overload in myopathic hamster hearts.
- Data indicate marked heterogeneity in cellular calcium distribution.
- Localized calcium increases are associated with necrotic cells and extracellular deposits.
Abstract:
In the Syrian cardiomyopathic hamster heart, abnormal cellular calcium regulation, resulting in cellular calcium overload, is believed to play a role in the pathogenesis of cardiac hypertrophy and failure. Alternatively, the primary abnormality may be coronary vasospasm, resulting in reperfusion-induced necrosis. According to the latter hypothesis, only those cells that suffer an ischemic insult would contain elevated calcium levels. To determine whether a generalized elevation in myocytic calcium exists in myopathic hamster hearts, we measured cellular and subcellular calcium concentrations by electron probe microanalysis in cryosections of 50-day and 96-day myopathic and control hearts, rapidly frozen in vivo. Total calcium content of ventricular homogenates from each group was also measured by atomic absorption spectrophotometry. No significant differences in subcellular calcium were found by electron probe microanalysis among 50-day and 96-day myopathics and their age-matched controls. In 50-day myopathic and control hearts, mitochondrial calcium was 0.7 +/- 0.2 and 0.9 +/- 0.2, respectively, and A-band calcium was 3.0 +/- 0.4 and 2.6 +/- 0.4 mmol calcium/kg dry wt(+/- SEM). Results from 96-day animals were similar. Localized regions of elevated calcium were found only at sites of necrotic foci: in Na+-loaded cells (mitochondria: 4.7 +/- 1.3 (SEM) mmol/kg dry wt), in dying cells (mitochondria: 72 +/- 22 (SEM) mmol/kg dry wt) or as extracellular deposits (7-10 mol/kg dry wt). Total calcium content of hearts from myopathic hamsters, as determined by atomic absorption spectrophotometry, was also 13 times (50-day) and 50 times (96-day) higher than controls. These results demonstrate that there is a marked heterogeneity in cellular calcium content in myopathic hamster hearts, but the data do not support the hypothesis of a generalized cellular calcium overload.