Thermal inactivation of membrane proteins, volume-dependent Na+, K(+)-cotransport, and protein kinase C activator-induced changes of the shape of human and rat erythrocytes.

The heat sorption curves for human and rat erythrocyte membranes in the temperature region from 40 degrees C to 90 degrees C have been compared resulting from thermal gel analysis of these membranes. The main heat sorption peaks are located within the temperature regions from 49 degrees C to 52 degrees C (A transition), from 56 degrees C to 59 degrees C (B transition), from 62 degrees C to 65 degrees C (C transition) and from 74 degrees C to 82 degrees C (D transition). Thermoinactivation temperatures for most of the membrane proteins in human and rat erythrocytes are rather different, which suggests essential differences in the arrangement of their membrane frameworks. Addition of the protein kinase C activator TPA induces a fast increase in light scattering of human and rat erythrocyte suspension which is connected with some changes of cell shape. This reaction is completely blocked by a minimal thermal treatment of the membrane framework proteins (preincubation at the temperature of the A transition). Such treatment inhibits also the increase of Na+, K(+)-cotransport in rat erythrocytes induced by hyperosmotic shrinkage. It is assumed that the proteins of the membrane framework take part in the volume-dependent regulation of the ion-transport systems of plasma membranes.