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NHE- and diffusion-dependent proton fluxes across the tubular system membranes of fast-twitch muscle fibers of the rat
- Source :
- Journal of General Physiology. 150:95-110
- Publication Year :
- 2017
- Publisher :
- Rockefeller University Press, 2017.
-
Abstract
- The complex membrane structure of the tubular system (t-system) in skeletal muscle fibers is open to the extracellular environment, which prevents measurements of H+ movement across its interface with the cytoplasm by conventional methods. Consequently, little is known about the t-system’s role in the regulation of cytoplasmic pH, which is different from extracellular pH. Here we describe a novel approach to measure H+-flux measurements across the t-system of fast-twitch fibers under different conditions. The approach involves loading the t-system of intact rat fast-twitch fibers with a strong pH buffer (20 mM HEPES) and pH-sensitive fluorescent probe (10 mM HPTS) before the t-system is sealed off. The pH changes in the t-system are then tracked by confocal microscopy after rapid changes in cytoplasmic ionic conditions. T-system sealing is achieved by removing the sarcolemma by microdissection (mechanical skinning), which causes the tubules to pinch off and seal tight. After this procedure, the t-system repolarizes to physiological levels and can be electrically stimulated when placed in K+-based solutions of cytosolic-like ionic composition. Using this approach, we show that the t-system of fast-twitch skeletal fibers displays amiloride-sensitive Na+/H+ exchange (NHE), which decreases markedly at alkaline cytosolic pH and has properties similar to that in mammalian cardiac myocytes. We observed mean values for NHE density and proton permeability coefficient of 339 pmol/m2 of t-system membrane and 158 µm/s, respectively. We conclude that the cytosolic pH in intact resting muscle can be quantitatively explained with respect to extracellular pH by assuming that these values apply to the t-system membrane and the sarcolemma.
- Subjects :
- 0301 basic medicine
HEPES
Sarcolemma
Physiology
Chemistry
Membrane structure
60807 Animal Structure and Function
03 medical and health sciences
Cytosol
Sodium–hydrogen antiporter
chemistry.chemical_compound
030104 developmental biology
Membrane
FOS: Biological sciences
60106 Cellular Interactions (incl. Adhesion, Matrix, Cell Wall)
Extracellular
Biophysics
Myocyte
60603 Animal Physiology - Systems
Subjects
Details
- ISSN :
- 15407748 and 00221295
- Volume :
- 150
- Database :
- OpenAIRE
- Journal :
- Journal of General Physiology
- Accession number :
- edsair.doi.dedup.....f3daf40c3a73fd1fda96902b6a2b293e