In vascular smooth muscle cells and several other cell types, inhibition of Na + ⁄K + -ATPase leads to the expression of early response genes, including c-Fos. We designed this study to examine whether or not a putative Na + i ⁄K + i-sensitive element is located within the c-Fos5¢-UTR from )650 to +103 containing all known response elements activated by ‘classic’ stimuli, such as growth factors and Ca 2+ i-raising compounds.