OBJECTIVE: Atrial natriuretic peptide (ANP) regulates the homeostasis of body fluid and blood pressure as a neuropeptide in the central nervous system. To assess the possible physiological role in the inner ear, we investigated the expression of ANP in primary culture of marginal cells, and then we detected the expression of ANP and its receptor (NPR-A) in cochlear tissues derived from neonatal and adult rats of various ages.
METHODS: Marginal cells were isolated from cochlear stria vascularis of the neonatal rats. The cultured cells were subsequently characterized by morphology, immunocytochemistry, and scanning electron microscope (SEM) analysis. In order to examine the expression of ANP in marginal cells as well as in the developing rats' cochleae, immunocytochemistry and reverse-transcription polymerase chain reaction (RT-PCR) were applied respectively.
RESULTS: The present study demonstrated typical characteristics of marginal cells, including cobblestone, polygonal monolayer, pleomorphic growth pattern and the expression of cell type-specific marker, and SEM analysis. Subsequently, immunoreactive product of ANP were found in cultured marginal cells. The mRNAs encoding ANP and NPR-A receptor was expressed in rats' cochleae from postembryonic stage to early postnatal period. During the maturation stage, ANP expression was gradually down-regulated, while the expression of NPR-A receptor was relatively stable.
CONCLUSION: ANP might be synthesized and secreted by marginal cells of stria vascularis, and could play an important role in modulating the microenvironment of the inner ear. In addition, ANP might contribute to development and growth process of cochlea.