Ionic changes accompanying astrocytic intercellular calcium waves triggered by mechanical cell damaging stimulation

Mechanically poking or damaging a single cell within a confluent astrocyte culture produces the so-called intercellular calcium (Ca2+) waves, that is, cell-to-cell propagating changes of intracellular free Ca2+. We were interested whether intercellular Ca2+ waves are also associated with changes in other intra- or extracellular ions. To that purpose, we investigated spatiotemporal changes of intracellular Ca2+ (Ca2+), sodium (Na-i(+)) and protons (H-i(+)) in primary cultures of rat cortical astrocytes using microfluorescence imaging with fura-2, SBFI and BCECF, respectively; changes of extracellular potassium (K-e(+)) were monitored with K+-sensitive microelectrodes. Mechanical damage to a single cell by stimulation with a piezo-electrically driven micropipette initialed intercellular Ca2+ waves that propagated to about 160 mu m away from the stimulation point. Na-i(+) increases could be detected in cells located 2-3 cell diameters from the stimulated cell, acidification was observed 1-2 cell diameters away and K-e(+) increases were measured up to 75 mu m away. Kinetic analysis suggests that the Na-i(+) and H-i(+) changes occur after, and thus secondary to the Ca-i(2+) changes. In contrast, K-e(+) changes occurred very fast, even before the Ca-i(2+) changes, but their propagation speed was too fast to implicate them as a trigger of Ca-i(2+) changes. As Na-i(+) is an important regulator of glycolysis in astrocytes, we hypothesize that astrocytic Na-i(+) changes in cells located remotely from a damaged cell might be a signal that activates glycolysis thereby producing more lactate that is transferred to the neurons and increases their energy potential to survive the inflicted damage. (C) 2000 Elsevier Science B.V. All rights reserved.