OBJECTIVES: To examine whether the atrial natriuretic peptide receptor (NPR-A) is present in the secretory regions of the membrane labyrinth of the adult mouse inner ear.
SETTING: Recent studies have implied that the homeostasis of endolymph fluid in the inner ear may be regulated by receptor-mediated mechanisms. Several studies have identified the presence of atrial natriuretic peptide receptors in the inner ear of guinea pig and rat. As a member of the natriuretic peptide receptor family, which also includes B-type natriuretic peptide receptor (NPR-B) and C-type natriuretic peptide receptor (NPR-C), NPR-A may be involved in the regulation of fluid homeostasis in the inner ear.
METHODS: In this study, samples of stria vascularis, nonstrial tissue of the cochlear lateral wall and vestibular organ tissue from the ears of 6 adult mice were obtained by immediate excision of bony labyrinth under operating microscope after decapitation. Total RNA was isolated and mRNA was amplified by the reverse transcription-polymerase chain reaction (RT-PCR) using consensus primers flanking a region of 127 bp at the target sequence. Mouse renal cortex known to contain NPR-A was used as a positive control.
RESULTS: We demonstrated that NPR-A was expressed in the mouse stria vascularis as well as in the nonstrial tissue of the cochlear lateral wall and vestibular organ.
CONCLUSION: These results suggest that natriuretic peptides may play an important role in maintaining the fluid homeostasis of inner ear endolymph via interaction with NPR-A.