Mechanisms of intercellular calcium signaling in glial cells studied with dantrolene and thapsigargin

Mechanical stimulation of a single cell in a primary mixed glial cell culture induced a wave of increased intracellular calcium concentration ([Ca 2+ ] i ) that was communicated to surrounding cells. Following propagation of the Ca 2+ wave, many cells showed asynchronous oscillations in [Ca 2+ ] i . Dantrolene sodium (10 μM) inhibited the increase in [Ca 2+ ] i associated with this Ca 2+ wave by 60‐80%, and prevented subsequent Ca 2+ oscillations. Despite the markedly decreased magnitude of the increase in [Ca 2+ ] i , the rate of propagation and the extent of communication of the Ca 2+ wave were similar to those prior to the addition of dantrolene. Thapsigargin (10 nM to 1 μM) induced an initial increase in [Ca 2+ ] i ranging from 100 nM to 500 nM in all cells that was followed by a recovery of [Ca 2+ ] i to near resting levels in most cells. Transient exposure to thapsigargin for 2 min irreversibly blocked communication of a Ca 2+ wave from the stimulated cell to adjacent cells. Glutamate (50 μM) induced an initial increase in [Ca 2+ ] i in most cells that was followed by sustained oscillations in [Ca 2+ ] i in some cells. Dantrolene (10 μM) inhibited this initial [Ca 2+ ] i increase caused by glutamate by 65‐90% and abolished subsequent oscillations. Thapsigargin (10 nM to 1 μm) abolished the response to glutamate in over 99% of cells. These results suggest that while both dantrolene and thapsigargin inhibit intracellular Ca 2+ release, only thapsigargin affects the mechanism that mediates intercellular communication of Ca 2+ waves. These findings are consistent with the hypothesis that inositol trisphosphate (IP 3 ) mediates the propagation of Ca 2+ waves whereas Ca 2+ ‐induced Ca 2+ release amplifies Ca 2+ waves and generates subsequent Ca 2+ oscillations.