Tellurite effect on ATPase activity of contractile membrane protein.

The effect of tellurite on ATPase activity of the contractile membrane protein in human erythrocytes was studied. Tellurite, even at a concentration of 0.01 mM, inhibited 25 per cent of the saponin-stimulated ATPase activity of the contractile membrane protein; the inhibition increased with increasing tellurite concentration, and was reversible.

Red blood cells under mechanical stress.

The effect of mechanical stress on erythrocytes suspended in various media was studied. The ability of the cells to increase their glucose consumption was found to be the major criterion allowing to divide the media into two groups. In plasma, serum or in Ringer's solution supplemented with albumin and glucose the energy consumption by mechanically stressed erythrocytes increased 20 to 50%; no morphological changes of the cells were observed either in suspension or on Giemsa smears.

Dual effect of calcium on erythrocyte membrane contraction.

Effect of different calcium concentrations on erythrocyte ghost shape and size has been studied. Erythrocyte ghosts are smallest at approximately 10 microM of total calcium content and in the absence of EDTA; both decrease and increase of free Ca2+ results in expansion of ghosts. Changes in erythrocyte ghost size occur at equal Ca2+ concentrations which, as it has been already found, alter ATPase activity of contractile membrane protein.

Energy requirements of erythrocytes under mechanical stress.

Factors influencing an increase of glucose consumption in erythrocytes under mechanical stress were studied. Under the shear stress of 2000-5000 s-1 the glucose consumption goes up 20-50%. This effect disappears in protein-free media, in Ca2+-free media and in resealed red ghosts; in all these cases certain morphological deviations were observed in the stressed cells.

Is Ca2+ effect on passive K+ transport mediated by spectrin--dependent ATPase?

The aim of this report was to find which part of the membrane is responsible for the Ca2+ dependence of membrane permeability to K+. We found that the enzyme activity of large contractile complex of membrane proteins, the so called spectrin-dependent ATPase (sp-ATPase) increases at certain Ca2+ concentrations when K+ permeability decreases and vice versa. Ca2+ apparent dissociation constant for sp-ATPase is 6 X 10(-7) M which is the value corresponding to findings of Porzig and Stoffel (1978) for Ca2+ binding to membrane with low K+ permeability.