Impairment of Na+-dependent amino acid transport in a cultured human T-cell line by hyperthermia and irradiation.

We have examined the effects of hyperthermia and radiation on the ability of a human T-leukemic lymphocyte line (Molt-4) to transport the Na+-dependent amino acid, 2-aminoisobutyrate (AIB). Heating Molt-4 at 43 degrees for 1 to 4 hr damages the ability of these cells to accumulate AIB. The damage to the transport system at 43 degrees impairs only the maximal rate of AIB uptake, i.e., Vmax. The thermal effect on AIB transport parallels the radiation effects observed for this system. Preliminary data indicate that heat and radiation may induce irreversible transitions in the tertiary or quaternary structure of a plasma membrane protein involved in regulating Na+-dependent amino acid transport. However, the mechanism by which heat and radiation damage this protein is different.