THE change in shape of erythrocytes from the normal biconcave disk to a spiculed sphere (echinocyte1) can be caused by an increased intracellular concentration of Ca2+ (refs 2 to 5). We have found that an immediate biochemical effect of raising intracellular [Ca2+] is to increase the production of 1,2-diacylglycerol and cause its accumulation in the plasma membrane. This change in membrane composition may alter the structure of the membrane and thus cause the change in shape. Energy-depleted cells also show increased 1,2-diacylglycerol and similar but less extreme morphological changes, even in the absence of Ca2+.
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