Two structurally distinct calcium storage sites in rat cardiac sarcoplasmic reticulum: an electron microprobe analysis study

Journal Article · Thu Dec 01 00:00:00 EST 1988 · Circ. Res.; (United States)

DOI:https://doi.org/10.1161/01.RES.63.6.1060· OSTI ID:6517731

Jorgensen, A O; Broderick, R; Somlyo, A P; Somlyo, A V

The elemental composition of subcellular organelles in resting rat papillary muscle was measured by electron probe x-ray microanalysis of cryosections of flash-frozen tissue. Nonmitochondrial electron-dense structures (50-100 nm in diameter) with a phosphorous concentration larger than 375 mmol/kg dry wt were identified in the interfibrillar spaces of the I band region. They were not visible in the proximity of transverse tubules. The sodium, magnesium, phosphorus, sulfur, chlorine, and potassium content of the electron dense structures showed a normal distribution, consistent with a uniform composition of a specific subcellular organelle. However, the distribution of the calcium concentrations in these electron-dense structures was bimodal, suggesting that they are composed of at least two subpopulations. One subpopulation had relatively high calcium (up to 53 mmol/kg dry wt) content with a mean value of 12.5 +/- 1.1 mmol/kg dry wt, while the other one had a relatively low calcium content with a mean value of 2.8 +/- 0.3 mmol/kg dry wt. The mean calcium concentration in the junctional sarcoplasmic reticulum (j-SR) in rat papillary muscle with calcium concentrations larger than 6 mmol/kg dry wt was 14.6 +/- 2.0 mmol/kg dry wt. We propose that the electron-dense structures described above correspond to nonjunctional sarcoplasmic reticulum and that the population containing relatively high calcium concentrations is calsequestrin-containing corbular sarcoplasmic reticulum (c-SR) confined to the I band region, while the population containing relatively low calcium concentrations corresponds to anastomosing regions of the network sarcoplasmic reticulum that lack calsequestrin.

• Research Organization: Univ. of Toronto (Canada)
• OSTI ID: 6517731
• Journal Information: Circ. Res.; (United States), Vol. 63:6
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
CALCIUM
SUBCELLULAR DISTRIBUTION
SARCOPLASMIC RETICULUM
MOLECULAR STRUCTURE
CHEMICAL COMPOSITION
ELECTRON MICROPROBE ANALYSIS
MUSCLES
MYOCARDIUM
RATS
ALKALINE EARTH METALS
ANIMALS
BODY
CARDIOVASCULAR SYSTEM
CELL CONSTITUENTS
CHEMICAL ANALYSIS
DISTRIBUTION
ELEMENTS
HEART
MAMMALS
METALS
MICROANALYSIS
ORGANOIDS
ORGANS
RODENTS
VERTEBRATES
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