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Effects of NaCl removal on osmolyte fluxes and regulatory volume decrease in cultured astrocytes
O Quesada1, E González, S Morales-Mulia
1Institute of Cell Physiology, Department of Byophysics, National University of Mexico, Mexico City.
Journal of Neuroscience Research
|July 22, 1998
Summary
Regulatory volume decrease (RVD) in astrocytes is accelerated by removing sodium chloride (NaCl). This enhances the efflux of potassium (K) and chloride (Cl), leading to faster cell volume recovery.
Area of Science:
- Cellular Physiology
- Neuroscience
- Biophysics
Background:
- Cultured cerebellar astrocytes regulate cell volume via ion and organic osmolyte extrusion.
- Regulatory Volume Decrease (RVD) is a critical homeostatic mechanism.
- Astrocytes swell in response to hyposmotic stress.
Purpose of the Study:
- To investigate the role of sodium chloride (NaCl) in regulating RVD in astrocytes.
- To determine the ionic and molecular mechanisms underlying RVD acceleration.
- To elucidate the impact of NaCl removal on ion and osmolyte efflux pathways.
Main Methods:
- Cell swelling induced in hyposmotic media (50% dilution).
- Measurement of RVD rate constants (k) and cell volume recovery.
- Tracer flux measurements for potassium (86Rb), chloride (125I), and organic osmolytes (taurine, D-aspartate).
- Ionic substitutions in the extracellular medium (e.g., replacing NaCl with sugars, polyalcohols, or altering cation/anion composition).
Main Results:
- Replacing NaCl with sugars/polyalcohols markedly accelerated RVD (k increased to 0.37-0.39 min(-1)), achieving full recovery in 3-5 min.
- NaCl removal significantly increased potassium (K) efflux (86Rb) by 80% and enhanced taurine/D-aspartate release by 25%.
- Delayed inactivation of chloride (Cl) efflux (125I) was observed upon NaCl removal.
- Ionic substitutions (Na+ or Cl-) partially accelerated RVD and K+ efflux, suggesting NaCl's general role.
Conclusions:
- NaCl removal significantly accelerates astrocyte RVD, primarily by enhancing K+ efflux and delaying Cl- efflux.
- The observed acceleration is attributed to alterations in the electrochemical gradient, increasing the driving force for K+ and facilitating amino acid release.
- Secondary effects of NaCl removal, such as changes in surface charge, ionic strength, intracellular calcium ([Ca]i), and intracellular sodium ([Na]i), may also modulate K+ efflux pathways.