Ion transport and its regulation in the endolymphatic sac (ES) are reviewed on the basis of recent lines of evidence. The morphological and physiological findings demonstrate that epithelial cells in the intermediate portion of the ES are more functional in ion transport than those in the other portions. Several ion channels, ion transporters, ion exchangers, and so on have been reported to be present in epithelial cells of ES intermediate portion. An imaging study has shown that mitochondria-rich cells in the ES intermediate portion have a higher activity of Na+, K+-ATPase and a higher Na+ permeability than other type of cells, implying that molecules related to Na+ transport, such as epithelial sodium channel (ENaC), Na+–K+–2Cl− cotransporter 2 (NKCC2) and thiazide-sensitive Na+–Cl− cotransporter (NCC), may be present in mitochondria-rich cells. Accumulated lines of evidence suggests that Na+ transport is most important in the ES, and that mitochondria-rich cells play crucial roles in Na+ transport in the ES. Several lines of evidence support the hypothesis that aldosterone may regulate Na+ transport in ES, resulting in endolymph volume regulation. The presence of molecules related to acid/base transport, such as H+-ATPase, Na+–H+ exchanger (NHE), pendrin (SLC26A4), Cl−–HCO3
− exchanger (SLC4A2), and carbonic anhydrase in ES epithelial cells, suggests that acid/base transport is another important one in the ES. Recent basic and clinical studies suggest that aldosterone may be involved in the effect of salt-reduced diet treatment in Meniere’s disease.
This study compared the utility of 39-deoxy-39-18 F-fluorothymidine PET ( 18 F-FLT PET) with that of 18 F-FDG PET for assessment of the early locoregional clinical outcomes of chemoradiotherapy for head and neck squamous cell carcinomas. Methods: From May 2006 to September 2010, 28 patients with head and neck squamous cell carcinomas underwent 18 F-FLT and 18 F-FDG PET before radiation therapy (RT), 4 wk after the initiation of RT, and 5 wk after completion of RT. PET images were evaluated qualitatively for regions of focally increased metabolism and were analyzed in relation to residual accumulation and local disease control. Results: During RT, 18 F-FLT uptake decreased more significantly than 18 F-FDG uptake. 18 F-FLT accumulations disappeared in 34 of 54 lesions (63%), and negative predictive value was 97%. 18 F-FDG PET during RT also had a high negative predictive value (100%), but only 9 lesions (16%) showed complete absence of accumulation. The specificity and overall accuracy of 18 F-FLT PET were significantly higher than those of 18 F-FDG PET both during and after RT. In particular, high significance was attributable to the results of the evaluations of primary lesions. There were significant differences in 3-y local control between the residual-accumulation and no-accumulation groups on both posttreatment 18 F-FLT PET (P , 0.0001) and posttreatment 18 F-FDG PET (P 5 0.0081). Conclusion: 18 F-FLT PET during RT and early follow-up facilitates the selection of optimal further therapy and the prediction of outcomes.
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