The effect of heat shock on amino acid transport and cell volume in 3T3 cells

In 3T3 cells temperatures higher than physiological stimulated amino acid t ransport activity in a dose-dependent manner up to 44 degreesC. However, th e temperature increase did not induce widespread transport increase of all other nutrients tested. The activities of both amino acid transport systems A and ASC were enhanced within a few minutes following cell exposure to in creased temperature. The maintenance of this effect required continuous exp osure of the cells to hyperthermia. Kinetic analysis indicated that the sti mulation of the activity of transport System A occurred through a mechanism affecting Vmax rather than Km, The continuous presence of cycloheximide di d not prevent the transport changes induced by hyperthermia. These results suggest that the increased amino acid uptake reflects an activation or relo cation of existing amino acid transport proteins. During the hyperthermic t reatment, the content of ninhydrin-positive substances (NPS), mostly amino acids, increased within the cells and the accumulation of these compatible osmolytes was parallelled by an increase in cell volume. The withdrawal of amino acids from the culture medium immediately before and during the shock phase counteracted the increase and reduced the NPS content but did not pr event the increase in amino acid transport, the cell swelling and the induc tion of the heat shock response.