in contrast to the single metallothionein ( mt)-1 gene of the mouse , the human mt-1 gene family is composed of seven active genes and six pseudogenes . in this study , the expression of mrna representing the seven active human mt-1 genes was determined in cultured human proximal tubule ( hpt ) cells under basal conditions and after exposure to the metals cd2 + , zn2 + , cu2 + , hg2 + , ag2 + , and pb2 + . 
 basal expression of mt-1x and mt-1e mrna in hpt cells was similar to expression of the housekeeping gene glyceraldehyde 3-phosphate dehydrogenase . 
 in contrast , mrnas representing the basal expression of mt-1a and mt-1f were a minor transcript in hpt cells . 
 treatment of hpt cells with cd2 + , zn2 + , or cu2 + increased the levels of mt-1e and mt-1a mrna , but not the levels of mt-1x or mt-1f mrna . 
 the increase in mt-1e mrna appeared to be influenced mainly by exposure to the various metals , whereas the increase in mt-1a mrna was influenced more by exposure to a metal concentration eliciting a loss of cell viability . 
 treatment of hpt cells with the metals hg2 + , ag2 + , and pb2 + was found to have no effect on the level of mt-1 mrna at either sublethal or lethal concentrations . 
 using hpt cells as a model , these results suggest that new features of mt gene expression have been acquired in the human due to the duplication of the mt-1 gene.imagesfigure 1figure 2figure 3figure 4figure 5figure 6figure 7figure 8figure 9figure 10figure 11figure 12