Membrane carrier-activity in X- or .GAMMA.-irradiated human diploid fibroblasts.

As protein molecules constitute 60% by mass of all membranes, one might expect to detect radiationinduced lesions in this compartment. The efficiency of the two carrier-proteins for D-glucose and glycine were determined post-irradiation (p.r.). A finite line of human diploid fibroblasts was used for this purpose. Quiescent Phase II cultures were exposed to 1, 5, 10, 30, 50 and 100 Gy X-rays and to 2.103 and 5.103 Gy 60Co-γ-rays. For each given dose, cells were detached enzymatically for measurements of their transport capabilities at time-intervals ranging from 30 mins. to 21 days p.r. The affinity to substrate (KM), maximal transport rate (Vmax) and the rate constant of the non-saturable component (KNS) were measured. Vmax varied depending on the criterium considered i.e. maximal transport rate per cell number, per unit volume cell space and per unit area cell surface. This incongruity was due to the concomitant increase in cell volume with time p.r. Soon after irradiation and even days later, no impairment in either Vmax or KM was detectable for either D-glucose or glycine for doses up to 100 Gy. At doses of 2.103 and 5.103 Gy, a 50% decrease in Vmax was observed. KM remained constant throughout.