AJP - Regulatory, Integrative and Comparative Physiology, Vol 265, Issue 2 474-R479, Copyright © 1993 by American Physiological Society
High-density localization of ANP receptors in chondrocytes of eel gill cartilage
H. Sakaguchi, T. Katafuchi, H. Hagiwara, Y. Takei and S. Hirose
Department of Biological Sciences, Tokyo Institute of Technology, Japan.
Very high levels of atrial natriuretic peptide (ANP) receptor were found in
a quite unexpected tissue, i.e., the chondrocyte of the eel gill cartilage.
125I-labeled ANP binding assay indicated that the eel gill contains large
amounts of the receptor and its levels are much higher (> 10-fold) than
those in the other tissues examined, including the brain, kidney, head
kidney including steroidogenic interrenal cells, and gut. Autoradiography
using gill sections revealed dense localization of ANP receptors in the
chondrocytes of the cartilage as well as moderate localization in the
parenchymal cells. Biochemical and pharmacological characterization of the
chondrocyte receptor indicated that most of the receptors are type C
receptors, having a broad ligand specificity and a reduced M(r) of 68,000.
Because a hyaline cartilage in which chondrocytes reside lacks blood
vessels, and all metabolic exchange is by slow diffusion through the
matrix, the chondrocyte localization of the type C ANP receptor is notable
and may stimulate not only chondrocyte research but also studies on
physiological significance of the type C receptor, which is generally
considered to be merely a clearance (silent) receptor.
