A passive sodium transport inhibitory factor (inhibitin) released from leukaemic promyelocytes in culture

Previous studies have shown that myeloid leukaemic blast cells contain a heat stable factor which inhibits bidirectional sodium transport in normal erythrocytes. This study was undertaken to establish whether leukaemic promyelocytes in culture secrete this factor. Two cell-lines of leukaemic promyelocytes (HL-60 and JR) were grown and culture media from both reduced significantly the ouabain-insensitive sodium efflux rate constant, whereas conditioned culture medium (incubated like the cells in culture) had no inhibitory effect. Promyelocyte extract reduced significantly (P less than 0.01) the total sodium efflux rate constant from 0.393 +/- 0.030 (SD) to 0.311 +/- 0.060, and ouabain-insensitive efflux rate constant from 0.131 +/- 0.008 to 0.079 +/- 0.009 (P less than 0.001). The inhibitory factor was heat stable (80 degrees C for 30 min) and it inhibited sodium efflux through a pathway which was not inhibited by ouabain or frusemide. These studies suggest that leukaemic promyelocytes secrete the previously identified passive sodium transport inhibitory factor.