Robert I. Weed

Calcium-pH Interactions in the Production of Shape Change in Erythrocytes

Isovolumic change of erythrocyte shape from a disc to a sphere may occur as the result of exposure to a variety of chemical agents [6, 11, 13, 21, 30], changes in pH [21, 22, 24, 30, 31] or by virtue of ATP depletion [10, 19, 33, 34]. Up to a point, these shape changes are reversible upon removal of the agent, restoration of the pH or regeneration of intracellular ATP.

Divalent Cation Content of Normal and ATP-Depleted Erythrocytes and Erythrocyte Membranes

Recent studies have suggested a central role for alterations in cellular divalent cations in the pathogenesis of red cell damage during in vitro storage [27, 43, 45]. Copper and calcium are known to exchange between plasma and red cells. Passive exchange occurs between plasma free copper and non-erythrocuprein red cell copper, allowing copper to come to equilibrium between plasma and two cellular compartments [4]. Calcium, which enters the red cell by diffusion, is extruded by a process which requires energy [36]. Calcium exodus is mediated by a « pump » which is linked to a calcium-activated ATPase [20, 26, 37, 42, 44, 45, 46]. This phosphohydrolytic enzyme tranduces energy from adenosine triphosphate (ATP) for the work required for calcium extrusion against a steep gradient. Hence, the system in several respects is analogous to the red cell sodium pump [14]. Weed, La Celle and Merrill provided evidence for the physiological importance of the red cell calcium pump by demonstrating that calcium accumulation was accompanied by detrimental changes in biophysical properties of the cell [43]. Studies by Wins and Schoffeniels [45], and Palek, Curby and Lionetti [27, 28] also indicated that calcium ion has an effect on the red cell membrane in vitro, since it induced volume reduction (shrinkage), in part explained as being due to a conformational change in membrane protein.

Fractionation of spectrin by differential precipitation with calcium

Abstract The calcium-stimulated ATPase activity of spectrin can be substantially separated from the magnesium-stimulated activity by partial precipitation of spectrin with calcium. The precipitated Ca-ATPase fraction can be dissolved by dialysis against EDTA, and the resulting solution can be polymerized into characteristic spectrin fibrils. The supernatant contains Mg-ATPase and, either before or after dialysis, contains predominantly “torus” forms. The two fractions are essentially identical on gel electrophoresis, being composed primarily of the high molecular weight peptides with a constant level of minor bands. These results imply that the Ca-ATPase is associated firmly with the high molecular weight peptides.