Cellular mechanism for spontaneous calcium oscillations in astrocytes.
OBJECTIVE
To determine the Ca2+ source and cellular mechanisms of spontaneous Ca2+ oscillations in hippocampal astrocytes.


METHODS
The cultured cells were loaded with Fluo-4 AM, the indicator of intracellular Ca2+, and the dynamic Ca2+ transients were visualized with confocal laser-scanning microscopy.


RESULTS
The spontaneous Ca2+ oscillations in astrocytes were observed first in co-cultured hippocampal neurons and astrocytes. These oscillations were not affected by tetrodotoxin (TTX) treatment and kept up in purity cultured astrocytes. The spontaneous Ca2+ oscillations were not impacted after blocking the voltage-gated Ca2+ channels or ethylenediamine tetraacetic acid (EDTA) bathing, indicating that intracellular Ca2+ elevation was not the result of extracellular Ca2+ influx. Furthermore, the correlation between the spontaneous Ca2+ oscillations and the Ca2+ store in endoplasmic reticulum (ER) were investigated with pharmacological experiments. The oscillations were: 1) enhanced when cells were exposed to both low Na+ (70 mmol/L) and high Ca2+ (5 mmol/L) solution, and eliminated completely by 2 micromol/L thapsigargin, a blocker of sarcoplasmic reticulum Ca2+-ATPase; and 2) still robust after the application with either 50 micromol/L ryanodine or 400 micromol/L tetracaine, two specific antagonists of ryanodine receptors, but depressed in a dose-dependent manner by 2-APB, an InsP3 receptors (InsP3R) blocker.


CONCLUSIONS
InsP3R-induced ER Ca2+ release is an important cellular mechanism for the initiation of spontaneous Ca2+ oscillation in hippocampal astrocytes.
Wang
Tong-fei
TF
State Key Laboratory of Biomembrane and Membrane Biotechnology, College of Life Sciences, Peking University, Beijing 100871, China.
Zhou
Chen
C
Tang
Ai-hui
AH
Wang
Shi-qiang
SQ
Chai
Zhen
Z
D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000378:metabolism*; D001896:Boron Compounds / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D020013:Calcium Signaling; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002478:Cells, Cultured; D004492:Edetic Acid / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006624:Hippocampus / Q000166:cytology* / Q000378:metabolism; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000037:antagonists & inhibitors; D018613:Microscopy, Confocal; D009474:Neurons / Q000166:cytology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012433:Ryanodine / Q000494:pharmacology; D013748:Tetracaine / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology
D001896:Boron Compounds; D053496:Inositol 1,4,5-Trisphosphate Receptors; D013748:Tetracaine; D012433:Ryanodine; D013779:Tetrodotoxin; D019284:Thapsigargin; D004492:Edetic Acid; C109986:2-aminoethoxydiphenyl borate; D000252:Calcium-Transporting ATPases; D002118:Calcium