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The activity of the Na+/Ca2+ exchanger largely modulates the Ca2+i signal induced by hypo-osmotic stress in rat cerebellar astrocytes. The effect of osmolarity on exchange activity.

Abstract
We recently demonstrated that rat cerebellar Type-1 astrocytes express a very active Na(+)/Ca(2+) exchanger highly colocalized with ryanodine receptors (RyRs), which in turn play a key role in glutamate-induced Ca(2+) signaling through a calcium-induced calcium release (CICR) mechanism. In this work we have explored whether the Na(+)/Ca(2+) exchanger has any role in the Ca(2+)(i) signal induced by hypo-osmotic stress in these cells, using microspectrofluorometric measurements with Fura-2, pharmacological tools, and confocal microscopy image analysis. We present evidence for the first time that the increase in [Ca(2+)](i) in rat cerebellar Type-1 astrocytes, resulting from moderate hypotonic shock, is mediated by Ca(2+) release from ryanodine-operated Ca(2+)(i) stores, and that the magnitude of the intracellular Ca(2+) signal induced by hypotonicity in the short term (up to 240 s) is small and controlled by the activity of the Na(+)/Ca(2+) exchanger operating in its extrusion mode. With longer times in the hypotonic medium, intracellular Ca(2+) store depletion leads to Ca(2+) entry through store-operated Ca(2+) channels. We found it interesting that the activity of the Na(+)/Ca(2+) exchanger measured during this reverse mode operation (Ca(2+) entry in exchange for internal Na(+)) was found to be greatly increased in hypotonic solutions and decreased in hypertonic ones. The buffering of the [Ca(2+)](i) rise induced by hypo-osmotic stress may prevent excessive increases in [Ca(2+)](i), which otherwise might impair the normal function of this glial cell.
AuthorsHéctor Rojas, Magaly Ramos, Gustavo Benaim, Carlo Caputo, Reinaldo DiPolo
JournalThe journal of physiological sciences : JPS (J Physiol Sci) Vol. 58 Issue 4 Pg. 277-9 (Aug 2008) ISSN: 1880-6546 [Print] Japan
PMID18638422 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
Chemical References
  • Hypotonic Solutions
  • Ryanodine Receptor Calcium Release Channel
  • Sodium-Calcium Exchanger
  • Sodium
  • Calcium
Topics
  • Animals
  • Astrocytes (metabolism)
  • Calcium (metabolism)
  • Calcium Signaling
  • Cell Size
  • Cells, Cultured
  • Cerebellum (cytology, metabolism)
  • Hypotonic Solutions
  • Microscopy, Confocal
  • Microspectrophotometry
  • Osmotic Pressure
  • Rats
  • Rats, Sprague-Dawley
  • Ryanodine Receptor Calcium Release Channel (metabolism)
  • Sodium (metabolism)
  • Sodium-Calcium Exchanger (metabolism)
  • Spectrometry, Fluorescence
  • Time Factors

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