Pendrin, a Cl^-/anion exchanger encoded by the gene PDS, is highly expressed in the kidney, thyroid and inner ear epithelia and is essential for bicarbonate secretion, iodide accumulation and endolymph ion balance, respectively. This study aimed to define promoter regulatory elements essential for renal, thyroid and inner-ear epithelial-specific expression of human PDS (hPDS) and to explore the effect of ambient pH and aldosterone on hPDS promoter activity. Endogenous pendrin mRNA and protein were detected in renal HEK293, thyroid LA2 and inner ear VOT36 epithelial cell lines, but not in the fibroblast cell line, NIH3T3. A 4.2kb hPDS 5'-flanking DNA sequence and consecutive 5'-deletion products, were cloned into luciferase reporter vectors and transiently transfected into the above cell lines. Distinct differences in expression/activity of deduced positive/negative regulatory elements within the hPDS promoter between HEK293, LA2 and VOT36 cells were demonstrated, with only basal activity in NIH3T3 cells. Acidic pH (7.0-7.1) decreased, and alkaline pH (7.6-7.7) increased, hPDS promoter activity in transfected HEK293 and VOT36, but not in LA2 cells. Aldosterone (10^-8M) reduced hPDS promoter activity in HEK293, but had no effect in LA2 and VOT36 cells. These pH and aldosterone-induced effects on the hPDS promoter occurred within 96bp and 89bp regions, respectively, which likely contain distinct response elements to these modulators. Acidic pH and aldosterone decreased and alkaline pH increased endogenous pendrin mRNA level in HEK293 cells. In conclusion, pendrin-mediated HCO₃^- secretion in the renal tubule and anion transport in the endolymph may be regulated transcriptionally by systemic pH and aldosterone.