Store depletion-induced calcium influx in rat cerebellar astrocytes

Abstract

1. In rat cerebellar astrocytes, intracellular Ca2+ store depletion by receptor agonists or sarco(endo)plasmic reticulum Ca2+ ATPase inhibitors induced a transient increase in the intracellular Ca2+ concentration ([Ca2+]i) in the absence of extracellular Ca2+ and a sustained increase in its presence. 2. After 10 min treatment with thapsigargin, the [Ca2+]i was unaffected by removal of thapsigargin, but fell rapidly to the basal level when extracellular Ca2+ was removed, suggesting the involvement of capacitative Ca2+ entry (CCE); this effect was not seen until cells had been exposed to thapsigargin for at least 2 min. 3. Using the whole cell voltage clamp technique, a 60-100 pA inward current was activated by store depletion, the reversal potential ranging from -5 to 0 mV. 4. When extracellular Na+ was isotonically replaced by Tris, the thapsigargin-induced [Ca2+]i increase was enhanced, while the inward current was reduced, indicating that store-operated Ca2+ channels were permeable to Na+; however, they were not permeable to Sr2+ or Ba2+. 5. Thapsigargin-induced CCE remained the same in the presence of nifedipine, La3+ or Cd2+, while it was inhibited in the presence of SK&F96365. 6. In cerebellar astrocytes, inhibition of protein serine/threonine phosphorylation promoted CCE. 7. In conclusion, in rat cerebellar astrocytes, store depletion activated a CCE via channels which were permeable to Ca2+ and Na+ and regulated by phosphorylation.