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Natriuretic peptide receptors in the human endolymphatic sac
John L Dornhoffer1, Christopher Danner, Shulin Li
1Department of Otolaryngology/Head and Neck Surgery, University of Arkansas for Medical Sciences, 4301 W Markham, MS 543, Little Rock, AR 72205. DornhofferJohnL@uams.edu
Objective:
To examine human endolymphatic sac (ELS) tissue for atrial natriuretic peptide (ANP) receptor subtypes A, B, and C.
Design:
Pilot study.
Methods:
Immunohistochemical analysis of human ELS tissue specimens. The ANP receptors were characterized using the peroxidase/antiperoxidase method and polyclonal antibodies directed against each receptor subtype. The identity of the stain regarding receptor subclass was masked from the observer. Human kidney tissue known to contain all 3 receptor subtypes was used as a control. Presence of the receptor subclasses was confirmed using reverse transcriptase-polymerase chain reaction (RT-PCR) techniques.
Subjects:
Samples of ELS tissue were obtained at autopsy from 3 fresh cadaver specimens (6 ears) and as surgical specimens from 3 patients (1 for immunohistochemical analysis and 2 for RT-PCR) undergoing acoustic neuroma resection using the translabyrinthine approach.
Results:
The ANP type B receptors demonstrated moderate to strong reactivity in all 7 specimens, and mild to moderate staining to the ANP type C receptor was also noted. No appreciable reactivity to the ANP type A receptor was detected using immunohistochemical techniques. All 3 receptor subclasses were detected using RT-PCR.
Conclusions:
The ANP receptors are found within the human ELS, with a predominance of ANP type B based on the intensity of staining. The ANPs may be involved in fluid homeostasis in the inner ear. Based on these findings, C-type natriuretic peptide may be a more effective peptide within the human ELS for fluid regulation because its binding affinity is virtually exclusive for the ANP type B receptor.