Differential Expression of Phospholipase C Specific for Inositol Phospholipids at the Cell Surface of Rat Glial Cells and REF52 Rat Embryo Fibroblasts

Abstract: 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 phopholipase 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/106 cells), whereas in confluent cultures ecto‐PLC activity increased to approximately 300 pmol/min/106 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/106 cells) and by C6 glioma cells (approximately 100 pmol/min/106 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.

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