Molecular biological study of the endolymphatic sac

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The expression of mRNAs encoding epithelial Na^+ channel (ENaC) and hormone receptors (aldosterone, vasopressin and ANP receptors) in the endolymphatic sac (ES) of the rat was examined by PCR and in situ hybridization. After reverse-transcription of rat ES RNA,cDNA was amplified by PCR using pairs of primers specific to ENaC (-subunit) and aldosterone, vasopressin V1a, V1b, V2, ANP-A and ANP-B receptors. After subcloning of the PCR products, the nucleic acid sequences were determined. Next, the localization of expression of ENaC and those receptors in the ES was examined by in situ hybridization using 35S-labeled cRNA probes.Expressions of EnaC,aldosterone, vasopressin V1a and ANP-A receptors were detected in the ES by PCR.In situ hybridization revealed the presence of aldosterone receptor in epithelial cells of the intermediate portion of the ES,while it failed to show the presence of vasopressin V1a and ANP-A receptors. The results suggest the involvement of aldosterone in Na^+ transport of the ES.