Contact-inhibited revertant cell lines isolated from SV40-transformed cells. V. Contact inhibition of sugar transport

The transport of 2-deoxyglucose in BALB/c 3T3 cells, Simian virus 40-transformed BALB/c 3T3 (SVT2) cells, and concanavalin A-selected revertant cells of SVT2 has been measured. Sparsely-seeded BALB/c 3T3 cells transport the sugar at about one-fourth, and sparsely-seeded revertant cells at three-fourths, the rate of SVT2 cells. BALB/c 3T3 cells undergo a dramatic drop in sugar uptake at confluency, transporting sugar at about one-tenth the rate of subconfluent cells. Revertant cells (contact-inhibited variants of transformed cells) are similar in this respect, but the drop is only 5-fold. SVT2 cells show no such change in uptake over wide cell densities. Subconfluent BALB/c 3T3, SVT2, and revertant cells have similar K_m and V_max values for 2-deoxyglucose transport; however, confluent 3T3 and confluent revertant cells show a large increase in K_m and a 5-fold decrease in V_max as compared to their subconfluent counterparts or SVT2 cells—indications of a decreased number of transport sites and a decreased affinity of these sites for sugar when these cells make intimate contacts with each other. These data indicate that extensive changes in the architecture of the cell surface occur when contactinhibited cells are in close apposition with each other, regardless of the persistence of partially expressed SV40 genetic information, and are discussed with regard to the membrane compositions of these cell lines.