intact human fibroblasts take up thyroxine ( t4 ) even more rapidly than t3 , with maximum after 5 min , showing a lower affinity for t4 than for t3 and a negligible specific and saturable binding sites for t4 , the presence of a cellular transport system for t4 may be hypothesized , considering that iodothyronine cellular binding is increased by preincubation with low doses of t4 .
C0016030
fibroblasts
C0007634
cellular