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Impairment of Na⁺-dependent Amino Acid Transport in a Cultured Human T-Cell Line by Hyperthermia and Irradiation¹

Tufts-New England Medical Center, Department of Therapeutic Radiology, Radiobiology Division, Boston, Massachusetts 02111

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° for 1 to 4 hr damages the ability of these cells to accumulate AIB. The damage to the transport system at 43° impairs only the maximal rate of AIB uptake, i.e., V_max. 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.

¹ A preliminary report of this work was presented at the Second Intermational Symposium on Cancer Therapy by Hyperthermia and Radiation, Essen, West Germany, June 1977 (9). This work was supported by Grant 5P02 CA12178-06 from the National Cancer Institute.

Received 6/10/77. Accepted 10/ 5/77.