Cytoskeletal proteolysis during calcium-induced morphological transitions of human erythrocytes

An analysis was made of the rate, extent, and reversibility of the morphological transitions which were induced in human erythrocytes after loading with 150 microM or 1 mM Ca2+. The rate and extent of proteolytic cleavage of cytoskeletal proteins were monitored simultaneously, particularly those of the ankyrins and band 4.1, and were found not to reflect the rate of shape change. These observations were made when intact cells were incubated either in a buffer which supported glycolysis or in a simple isotonic Tris buffer without glucose. The composition of the buffer affected the initial morphology of the cells, the rate of morphological transition, the rate of proteolysis of cytoskeletal proteins, and the extent and kinetics of the reversal of morphology from the echinocyte to discocyte after removal of the ionophore A23187 and Ca2+. The morphology of cells transformed to spheroechinocytes by loading metabolically depleted cells for 15 min with 1 mM Ca2+, and which retained 50% band 2.1, was reversed in the presence of substrates for ATP synthesis to that of a mixture of 60% stage 1 echinocytes plus 25% discocytes, suggesting that ankyrin may not be essential for the maintenance of a disc-like morphology. Echinocytes which were depleted of greater than 50% band 4.1 were unable to undergo the transition back to discs.