INSULIN PRODUCES A BIPHASIC RESPONSE IN TETRAHYMENA-THERMOPHILA BY STIMULATING CELL-SURVIVAL AND ACTIVATING PROLIFERATION IN 2 SEPARATE CONCENTRATION INTERVALS

Cells of Tetrahymena may produce autocrine signal molecules with effec ts on survival and proliferation. Here we have tested the effects of h uman recombinant and bovine insulin, and the B22-B30 fragment of bovin e insulin over a wide range of concentrations (10(-5)-10(-18) M) on ce ll survival and proliferation in a synthetic nutrient medium. The cell s were grown in conical flasks at low initial cell densities (40 and 4 00 cells/ml). Insulin prevented rapid cell death and/or promoted cell proliferation over two separate concentration ranges: down to nanomola r levels and again in the low pico- and femtomolar range. At an initia l population density of 400 cells/ml the cells multiplied at both conc entration intervals. At 40 or fewer organisms/ml the cells multiplied in the high concentration interval, whereas in the low interval they s urvived for about four times longer than those in the control cultures . B22-B30 added to cultures of 40 initial cells/ml produced a stimulat ion of cell survival in the low pico- and high femtomolar range. In th e presence of hemin (50 nM) cells at 400 initial organisms/ml multipli ed at insulin concentrations down to about 3 nM and again from 300 aha to 10 pM. In some cases, hemin plus insulin activated cell proliferat ion between the two concentration intervals as well. At 40 cells/ml th e cells not only survived but proliferated in the femtomolar range. Ce lls in cultures supplemented with both hemin and B22-B30 multiplied at the low concentration interval (from about 100 fM to 10 pM). (C) 1996 Academic Press Limited