LONG-TERM EXPOSURE TO CHROMIUM(VI) OXIDE LEADS TO DEFECTS IN SULFATE TRANSPORT-SYSTEM IN CHINESE-HAMSTER OVARY CELLS

Chromium(VI) resistant Chinese hamster ovary (CHO) cell lines were est ablished in this study by exposing parental CHO-K1 cells to sequential increases in CrO3 concentration. The final concentration of CrO3 used for selection was 7 mu M for Cr7 and 16 mu M for Cr16 cells. Cr16-1 w as a subclone derived from Cr16 cells. Next, these resistant cells wer e cultured in media without CrO3 for more than 6 months. The resistanc e of these cells to CrO3 was determined by colony-forming ability foll owing a 24-h treatment. The LD(50) of CrO3 for chromium(VI) resistant cells was at least 25-fold higher than that of the parental tells. The cellular growth rate, chromosome number, and the hprt mutation freque ncy of these chromium(VI) resistant cells were quite similar to their parental cells. The glutathione level, glutathione S-transferase, cata lase activity, and metallothionine mRNA level in Cr7 and Cr16-1 cells were not significantly different from their parental cells. Furthermor e, Cr16-1 cells were as sensitive as CHO-K1 cells to free-radical gene rating agents, including hydrogen peroxide, nickel chloride, and metha nesulfonate methyl ester, and emetine, i.e., a protein synthesis inhib itor. The uptake of chromium(VI) and the remaining amount of this meta l in these resistant and the parental cell lines were assayed by atomi c absorption spectrophotometry. Experimental results indicated that a vastly smaller amount of CrO3 entered the resistant cell lines than th eir parental cells did. A comparison was made of the sulfate uptake ab ilities of CHO-K1 and chromium(VI) resistant cell lines. These results revealed that the uptake of sulfate anion was substantially reduced i n Cr7 and Cr16-1 cells. Extracellular chloride reduced sulfate uptake in CHO-K1 but not in Cr16-1 cells. Therefore, the major causative for chromium(Vl) resistance in these resistant cells could possibly be due to the defects in SO42-/C1(-) transport system for uptake chromium(VI ). (C) 1995 Wiley-Liss, Inc.