Circulation Research, Vol 63, 1060-1069, Copyright © 1988 by American Heart Association

ARTICLES

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

AO Jorgensen, R Broderick, AP Somlyo and AV Somlyo
Department of Anatomy, Faculty of Medicine, University of Toronto, Canada.

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.(ABSTRACT TRUNCATED AT 250 WORDS)

This article has been cited by other articles:

				C. V. Remillard, W.-M. Zhang, L. A. Shimoda, and J. S. K. Sham Physiological properties and functions of Ca2+ sparks in rat intrapulmonary arterial smooth muscle cells Am J Physiol Lung Cell Mol Physiol, August 1, 2002; 283(2): L433 - L444. [Abstract] [Full Text] [PDF]

				M. Hagedorn and A. Ziegler Analysis of Ca2+ uptake into the smooth endoplasmic reticulum of permeabilised sternal epithelial cells during the moulting cycle of the terrestrial isopod Porcellio scaber J. Exp. Biol., July 1, 2002; 205(13): 1935 - 1942. [Abstract] [Full Text] [PDF]

				I. Gombosova, P. Boknik, U. Kirchhefer, J. Knapp, H. Luss, F. U. Muller, T. Muller, U. Vahlensieck, W. Schmitz, G. S. Bodor, et al. Postnatal changes in contractile time parameters, calcium regulatory proteins, and phosphatases Am J Physiol Heart Circ Physiol, June 1, 1998; 274(6): H2123 - H2132. [Abstract] [Full Text] [PDF]

				R. E. Lesh, G. F. Nixon, S. Fleischer, J. A. Airey, A. P. Somlyo, and A. V. Somlyo Localization of Ryanodine Receptors in Smooth Muscle Circ. Res., February 9, 1998; 82(2): 175 - 185. [Abstract] [Full Text] [PDF]

				W. Chen, C. Steenbergen, L. A. Levy, J. Vance, R. E. London, and E. Murphy Measurement of Free Ca[IMAGE] in Sarcoplasmic Reticulum in Perfused Rabbit Heart Loaded with 1,2-Bis(2-amino-5,6-difluorophenoxy)ethane-N,N,N`,N`-tetraacetic Acid by [IMAGE]F NMR J. Biol. Chem., March 29, 1996; 271(13): 7398 - 7403. [Abstract] [Full Text] [PDF]

				R. Zucchi, S. Ronca-Testoni, G. Yu, P. Galbani, G. Ronca, and M. Mariani Postischemic Changes in Cardiac Sarcoplasmic Reticulum Ca2+ Channels : A Possible Mechanism of Ischemic Preconditioning Circ. Res., June 1, 1995; 76(6): 1049 - 1056. [Abstract] [Full Text]