Radiation-induced changes in the cell membrane of cultured human endothelial cells.

We investigated the effect of irradiation on the kinetic characteristics of amino acid and glucose transport, and the effect on the activity of the cell membrane-bound enzyme 5'-nucleotidase and on the receptor-mediated stimulation of cyclic adenosine monophosphate synthesis by prostaglandin E1. Irradiation inhibited the sodium-dependent amino acid transport by a reduced binding of the amino acid to the transport unit. The transport of glucose, which appeared to be a sodium-independent process, was temporarily stimulated by increased maximal velocity of the transport. No effect was found on the binding to the transport unit. Irradiation increased the 5'-nucleotidase activity and decreased the prostaglandin E1-stimulated cyclic adenosine monophosphate synthesis 48 h after exposure to 20 Gy. It is concluded that irradiation decreases sodium-dependent transport by impairment of the transport unit, does not impair a sodium-independent process, and has opposite effects on membrane-bound enzyme activity and a receptor-mediated process.

Studies on the determination of extracellular galactosyltransferase in human intestinal tissue.

The determination of extracellular galactosyl transferase (EC 2.4.1.38) activity in human intestinal tissue by assessment of the incorporation of label after incubation with UDP[3H]galactose was evaluated. Intestinal biopsy specimens were incubated with membrane-permeable L-[1-14C]fucose and non-permeable UDP-D-[6-3H]galactose (UDP[3H]Gal). Comparison of the amounts of 3H- and 14C-label incorporated into subcellular fractions showed uptake and incorporation of galactose formed by the hydrolysis of UDP[3H]Gal by brush-border enzymes. The results indicate that incorporation of galactose after incubation of the tissue with UDP[3H]Gal is not exclusively attributable to extracellular galactosyl transferase.