Increased Activity of the Diastrophic Dysplasia Sulfate Transporter in Otosclerosis and Its Inhibition by Sodium Fluoride

Hypothesis This study investigates the function of the diastrophic dysplasia sulfate transporter (DTDST) in otosclerotic bone and the effect on it of sodium fluoride (NaF). Background Otosclerosis is a localized bone dystrophy with increased bone turnover. DTDST is implicated in the regulation of the bone turnover. Materials and methods Primary cultures of cells were obtained from the stapes and external auditory canal (EAC) of 26 patients with otosclerosis and from nine control patients. Sulfate uptake was quantified under basal conditions and with NaF. The NaF signaling pathways were investigated using forskolin and verapamil. Results The relative initial rates of sulfate uptake and the apparent Vmax values were: otosclerotic stapes > EAC > control stapes = control EAC. The sulfate uptake by the otosclerotic stapes was correlated with the loss of sensorineural hearing. The amounts of DTDST mRNA (RNase protection assay) in the four subgroups did not differ. NaF (10(-6)M, 1 hr) inhibited sulfate uptake by the otosclerotic stapes and EAC cells but not by control samples. Conclusion The authors believe that whether the increased DTDST activity is a cause or an effect of otosclerosis, it appears to be a specific target for NaF treatment.