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Imaging Local Ca2+ Signals in Cultured Mammalian Cells
Published on: March 3, 2015
Immunofluorescence localization of the Na-Ca exchanger in heart cells
R S Kieval1, R J Bloch, G E Lindenmayer
1Department of Physiology, School of Medicine, University of Maryland, Baltimore 21201.
Insights
The Na-Ca exchanger is found throughout the cardiac cell surface, including sarcolemma and T-tubules. This widespread distribution offers new insights into the role of sodium-calcium exchange in heart function.
Area of Science:
- Cardiovascular Physiology
- Cell Biology
- Molecular Cardiology
Background:
- The sodium-calcium exchanger (Na-Ca exchanger) plays a critical role in regulating intracellular calcium levels in cardiomyocytes.
- Understanding the precise localization of the Na-Ca exchanger is essential for elucidating its function in cardiac excitation-contraction coupling.
Purpose of the Study:
- To investigate the subcellular localization of the Na-Ca exchanger in isolated cardiac cells from rat and guinea pig.
- To determine the distribution of the Na-Ca exchanger across various membrane domains within cardiomyocytes.
Main Methods:
- Immunocytochemical techniques were employed on fixed, isolated heart cells.
- Epifluorescence and confocal microscopy were utilized to visualize the Na-Ca exchanger.
- Quantitative analysis of fluorescent foci distribution was performed.
Main Results:
- The Na-Ca exchanger was found to be distributed across all membranes interfacing with the extracellular space.
- Significant localization was observed in the sarcolemma, transverse tubules (T-tubules), and intercalated disks.
- Confocal imaging revealed a regular grid of Na-Ca exchanger foci in T-tubules, aligned with Z-lines, spaced at approximately 1.80 microns sarcomere-to-sarcomere and 1.22 microns along Z-lines.
Conclusions:
- The Na-Ca exchanger exhibits a widespread distribution on the cardiac cell surface.
- This extensive localization suggests a significant role for the Na-Ca exchanger in cellular calcium handling and cardiac function.
Abstract:
We investigated the localization of the Na-Ca exchanger in fixed, isolated heart cells from rat and guinea pig using immunocytochemical methods with epifluorescence and confocal microscopy. We found that the Na-Ca exchanger is distributed throughout all membranes in contact with the extracellular space, including the sarcolemma, the transverse tubules (T-tubules), and the intercalated disks. Microscopic nonuniformities in the fluorescent labeling appear to reflect varying views of the membranes containing Na-Ca exchanger protein. Confocal thin-section imaging reveals a regular grid of discrete foci of fluorescence, which represent Na-Ca exchanger in T-tubules viewed en face. These foci are 1.80 +/- 0.01 microns apart from sarcomere to sarcomere and are aligned with the Z-line. Along each Z-line, these foci are spaced at 1.22 +/- 0.11-microns intervals. Longitudinal sections of the sarcolemma-T-tubule junction show a comblike appearance, with T-tubules extending inward from the heavily labeled sarcolemma. Our finding that the Na-Ca exchanger is widely distributed over the cell surface may provide further insight into the role of Na-Ca exchange in the heart.
