Intracellular Ca2+ signals induced by ATP and thapsigargin in glioma C6 cells. Calcium pools sensitive to inositol 1,4,5-trisphosphate and thapsigargin

• Published in: Neurochemistry international 1997-07, Vol.31 (1), p.55-64
• Main Authors: SABAŁA, P, AMLER, E, BARANSKA, J
• Format: Article
• Language: English
• Subjects: Adenosine Triphosphate - pharmacology; Biological and medical sciences; Calcium - metabolism; Drug Evaluation, Preclinical; Endoplasmic Reticulum - drug effects; Endoplasmic Reticulum - metabolism; Enzyme Inhibitors - pharmacology; Fundamental and applied biological sciences. Psychology; Glioma - metabolism; Glioma - pathology; Humans; Inositol 1,4,5-Trisphosphate - pharmacology; Isolated neuron and nerve. Neuroglia; Signal Transduction - drug effects; Thapsigargin - pharmacology; Tumor Cells, Cultured; Vertebrates: nervous system and sense organs
• ISSN: 0197-0186; 1872-9754
• DOI: 10.1016/S0197-0186(96)00135-0

In glioma C6 cells, extracellular ATP generates inositol 1,4,5-trisphosphate (InsP3), indicating the presence of purinergic receptors coupled to phosphoinositide turnover. To identify the effect of ATP (acting via InsP3) and thapsigargin (acting without InsP3 production as a specific inhibitor of the endoplasmic reticulum Ca(2+)-ATPase) on intracellular Ca2+ pools we used video imaging of Fura-2 loaded into single, intact glioma C6 cells. It has been shown that ATP and thapsigargin initiate Ca2+ response consistent with the capacitative model of Ca2+ influx. When the cells were stimulated by increasing concentrations of ATP (1, 10, 50 and 100 microM) the graded, quantal Ca2+ response was observed. In the absence of extracellular Ca2+ thapsigargin and ionomycin-releasable Ca2+ pools are overlapping, demonstrating that Ca2+ stores are located mainly in the endoplasmic reticulum. After maximal Ca2+ mobilization by ATP, thapsigargin causes further increase in cytosolic Ca2+ concentration, whereas emptying of thapsigargin-sensitive intracellular stores prevents any further Ca2+ release by ATP. Thus, the thapsigargin-sensitive intracellular pool of Ca2+ in glioma C6 cells seems to be larger than that sensitive to InsP3. Two hypothesis to explain this result are proposed. One postulates a presence of two different Ca2+ pools, sensitive and insensitive to InsP3 and both discharged by thapsigargin, and the other, the same intracellular pool of Ca2+ completely emptying by thapsigargin and only partially by InsP3. These results may contribute to understanding the mechanism of Ca2+ signalling mediated by ATP, the most potent intracellular Ca2+ mobilizing agonist in all types of glial cells.