Store depletion-induced calcium influx in rat cerebellar astrocytes.
1. In rat cerebellar astrocytes, intracellular Ca(2+) store depletion by receptor agonists or sarco(endo)plasmic reticulum Ca(2+) ATPase inhibitors induced a transient increase in the intracellular Ca(2+) concentration ([Ca(2+)](i)) in the absence of extracellular Ca(2+) and a sustained increase in its presence. 2. After 10 min treatment with thapsigargin, the [Ca(2+)](i) was unaffected by removal of thapsigargin, but fell rapidly to the basal level when extracellular Ca(2+) was removed, suggesting the involvement of capacitative Ca(2+) 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 [Ca(2+)](i) increase was enhanced, while the inward current was reduced, indicating that store-operated Ca(2+) channels were permeable to Na(+); however, they were not permeable to Sr(2+) or Ba(2+). 5. Thapsigargin-induced CCE remained the same in the presence of nifedipine, La(3+) or Cd(2+), 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 Ca(2+) and Na(+) and regulated by phosphorylation.
Lo
Kuo-Jung
KJ
Department of Biochemistry, National Defense Medical Center, Taipei, Taiwan, Republic of China.
Luk
Hsiang-Ning
HN
Chin
Ting-Yu
TY
Chueh
Sheau-Huei
SH
D000818:Animals; D001253:Astrocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007424:Intracellular Fluid / Q000187:drug effects / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D010769:Phosphothreonine / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
D002121:Calcium Channel Blockers; D004791:Enzyme Inhibitors; D010769:Phosphothreonine; D010768:Phosphoserine; D002118:Calcium