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Endogenous calcium in sickle cells does not activate polyphosphoinositide phospholipase C
M D Rhoda1, J C Sulpice, P Gascard
1INSERM U 91, Hôpital Henri Mondor, Creteil, France.
The Biochemical Journal
|August 15, 1988
Summary
Sickle-cell-anaemia erythrocytes have altered phospholipid levels and turnover, but deoxygenation-induced calcium does not activate phospholipase C. Excess calcium in SS cells is compartmentalized, not freely available.
Area of Science:
- Biochemistry
- Hematology
- Cell Biology
Background:
- Sickle-cell-anaemia erythrocytes (SS cells) exhibit elevated intracellular calcium and deoxygenation-induced calcium uptake.
- Previous research suggested high calcium activates Ca2+-dependent K+ loss and Ca2+-sensitive polyphosphoinositide phospholipase C (PIC) in SS cells.
- The role of intracellular calcium in regulating phospholipid metabolism in SS cells requires further investigation.
Purpose of the Study:
- To investigate the effect of deoxygenation-induced calcium influx on polyphosphoinositide and phosphatidic acid metabolism in SS cells.
- To determine if endogenous calcium in SS cells activates phospholipase C activity.
- To characterize changes in phospholipid content and turnover in SS erythrocytes.
Main Methods:
- Analysis of phospholipid content (phosphatidylinositol 4,5-bisphosphate, phosphatidylinositol 4-phosphate, phosphatidic acid) in normal (AA) and SS erythrocytes.
- Measurement of deoxygenation-induced calcium entry into SS cells.
- Quantification of inositol 1,4,5-trisphosphate formation using ion-pair reverse-phase h.p.l.c.
- Assessment of 32P incorporation into phospholipids in response to deoxygenation.
Main Results:
- SS erythrocytes showed increased phosphatidylinositol 4-phosphate and decreased phosphatidic acid compared to AA cells, with no change in phosphatidylinositol 4,5-bisphosphate.
- Deoxygenation-induced calcium entry did not alter polyphosphoinositide or phosphatidic acid levels or their 32P-labeling.
- No inositol 1,4,5-trisphosphate formation was detected, indicating no Ca2+-dependent PIC activation.
- 32P incorporation into phospholipids was higher in SS cells than AA cells, irrespective of cell density.
Conclusions:
- Deoxygenation-induced calcium influx does not activate phospholipase C in SS cells.
- The excess calcium in SS cells appears to be compartmentalized and not freely available to activate intracellular enzymes.
- Increased phospholipid turnover in SS cells suggests alterations in lipid kinase/phosphatase activity or metabolic compartmentation, independent of acute calcium changes.