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.

• Authors: Héctor Rojas, Magaly Ramos, Gustavo Benaim, Carlo Caputo, Reinaldo DiPolo
• Journal: The journal of physiological sciences : JPS (J Physiol Sci) Vol. 58 Issue 4 Pg. 277-9 (Aug 2008) ISSN: 1880-6546 [Print] Japan
• PMID: 18638422 (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