A culture system was used to evaluate the radiosensitivity of CD4+ and CD8+ T cells, Leu 19+ cells, and B cells obtained from normal adult males. Unstimulated CD8+ lymphocytes (D0 = 55 cGy) were twice as radiosensitive as CD4+ cells (D0 = 115 cGy). B cells had an intermediate radiosensitivity (D0 = 100 cGy). Leu 19+ cells were much more radioresistant and expressed a D0 of 550 cGy. When lymphoid cells were irradiated 1 or 4 days before phytohemagglutinin (PHA) stimulation, they were more radiosensitive than if they were first stimulated with PHA and then irradiated. When lymphoid cells were irradiated 1 h after PHA stimulation each lymphocyte subset was characterized by an increase in the D0 to 150 cGy for B cells to 290 cGy for CD4+ cells, and to 240 cGy for CD8+ cells. In contrast, Leu 19+ cells exhibited a decrease in their D0 to 290 cGy after they were stimulated by PHA.

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The effect of hyperthermia (42OC) on K + transport has been examined by monitoring t h e uptake of 42KCI by Chinese hamster (line CHO) cells at both 37O and 42OC as well as 37OC following a 30-min treatment at 42OC. Early studies showed that CHO cells exhibit two components of uptake at both 37O and 42OC. Consequently, it was necessary to determine rate equations describing a three-compartment system (i.e., the bathing medium and two cellassociated compartments) and apply them to this system. Using the equations describing the behavior of the tracer in each compartment as well as the general solutions given by Robertson et al (1957), a method was developed for obtaining the two components of influx. The two transport rates were determined from equations arising from mathematical analysis and requiring only measurable quantities for their solutions. The results of this study showed that (1) both components of influx at 42OC are increased over influx at 37OC;(2) the increase is significant (by an average 68% for the rapid component and 55% for the slow component); and (3) the increase is due entirely to an increase in active transport. The increased active transport is both immediate and quickly reversible when cells are returned to 37OC; resumption of cell division is delayed for several additional hours, indicating that changes in potassium transport are not directly responsible for the prolonged delay in cell division. Rather, the results suggest that increased activity of the membrane pump may be the initial event in a series of events resulting from heat treatment.