Elimination of complement channels from the plasma membranes of U937, a nucleated mammalian cell line: temperature dependence of the elimination rate.

We have studied the release of radiolabeled small markers from nucleated cells carrying complement channels in order to determine the life-span of these channels at various temperatures. U937 cells, a human histiocytic cell line, were labeled with 14C-aminoisobutyric acid or 86RbCl, and treated with sublytic doses of C to form transmembrane channels. The cells were then incubated at various temperatures, and the persistence of channels was evaluated by measuring the release of the intracellular markers through the remaining channels. The results indicate that the life-span of the C channels in the plasma membranes of these cells varies markedly with temperature. Thus, at 2 degrees C, the half-life of the channels was about 2 hr, whereas at 37 degrees C, the half-life was estimated to be approximately 1 min. The rapid elimination of the transmembrane channels from the plasma membranes of these nucleated cells contrasts sharply with the long persistence of C channels in the membranes of erythrocytes or erythrocyte ghosts. It is likely that the multi-hit requirement recently reported for lysis of nucleated mammalian cells by C is due, at least in part, to the rapid disappearance of channels.