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.

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
  • 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

Join CureHunter, for free Research Interface BASIC access!

Take advantage of free CureHunter research engine access to explore the best drug and treatment options for any disease. Find out why thousands of doctors, pharma researchers and patient activists around the world use CureHunter every day.
Realize the full power of the drug-disease research network!

Choose Username:
Verify Password: