Effect of ionizing radiation on the transport of 2-aminoisobutyric acid in rat thymic and splenic lymphocytes

The effects of gamma-irradiation on the Na$sup +$-dependent 2- aminoisobutyric acid (AIB) transport system in rat thymic and splenic lymphocytes were compared. The results show that gamma-irradiation (0.25 to 10 krads) impairs the ability of lymphocytes from the thymus and spleen to accumulate AIB. The radiation effect is specific for this transport system since the transport of 1-aminocyclopentane-1-carboxylic acid (ACPC), a Na$sup +$-independent system, is not affected in either organ by the levels of radiation used. This suggests that the cells are not becoming leaky and that the mechanism which affects AIB transport in thymic lymphocytes is the same in splenic lymphocytes. The radiation effect is both time and dose dependent, but anomalies were found in the uptake of AIB in the splenic lymphocytes as a function of both parameters in irradiated and nonirradiated splenic lymphocytes. These anomalies suggested that splenic lymphocytes contained a sensitive population of cells. The effect of radiation on lymphocytes from spleens treated with anti-rat lymphocyte serum (ALS) was compared with the effect on lymphocytes from nontreated spleens. The population of lymphocytes remaining after ALS treatment was much more radioresistant. This indicated that the sensitive population of lymphocytes in the spleen with respect to AIB transportmore » was a thymus-derived cell population. Previously, insulin, which increases 2-aminoisobutyric acid influx by increasing the maximal rate of uptake, V/sub max/, was found to protect the thymocyte 2- aminoisobutyric acid system against the effects of radiation. In the case of splenic lymphocytes, no such protective effect was found. In both cases insulin (10$sup -7$ M to 10$sup -12$ M) stimulated AIB transport by 10 to 15 percent. This indicated that splenic lymphocytes do have insulin receptor sites but that the mechanism of the insulin radioprotective effect observed in thymocytes is not functioning in splenic lymphocytes. (auth)« less