Differential expression of phospholipase C specific for inositol phospholipids at the cell surface of rat glial cells and REF52 rat embryo fibroblasts.
Phosphatidylinositol(PI)-specific phospholipase C activity was detected on the surface of rat astrocytes, rat C6 glioma cells, and rat embryo (REF52) fibroblasts. The cell surface phospholipase C (ecto-PLC) activity was calcium-dependent, did not result from secreted phospholipase C, and was not released from the cell surface by bacterial PI-specific phospholipase C. Agents known to stimulate intracellular PI turnover, including carbachol, L-glutamic acid, acetylcholine, and orthovanadate, did not induce measurable alterations in the activity of the ecto-PLC. The expression of ecto-PLC activity by REF52 fibroblasts was density-dependent: subconfluent cultures of REF52 exhibited low levels of activity (less than 80 pmol of inositol phosphate formed/min/10(6) cells), whereas in confluent cultures ecto-PLC activity increased to approximately 300 pmol/min/10(6) cells. In contrast to this behavior and that exhibited by previously reported ecto-PLC-positive cell types, the ecto-PLC activity exhibited by astrocytes (approximately 1,000 pmol/min/10(6) cells) and by C6 glioma cells (approximately 100 pmol/min/10(6) cells) was independent of cell culture density up to confluence. The constitutive expression of ecto-PLC activity of astroglial cells may be related to their function as accessory cells in close association with neurons.
Birrell
G B
GB
Institute of Molecular Biology, University of Oregon, Eugene 97403.
Hedberg
K K
KK
Volwerk
J J
JJ
Griffith
O H
OH
D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000201:enzymology*; D002455:Cell Division; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology*; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000201:enzymology*; D004622:Embryo, Mammalian; D005347:Fibroblasts / Q000201:enzymology; D005910:Glioma / Q000201:enzymology*; D007328:Insulin / Q000494:pharmacology; D007700:Kinetics; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D010716:Phosphatidylinositols / Q000378:metabolism*; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism*; D051381:Rats; D013379:Substrate Specificity; D014407:Tumor Cells, Cultured
D007328:Insulin; D010716:Phosphatidylinositols; D010727:Phosphoric Diester Hydrolases; D043265:Phosphatidylinositol Diacylglycerol-Lyase