Morphological and functional characterization of a novel Na+/K+-ATPase-immunoreactive, follicle-like structure on the gill septum of Japanese banded houndshark, Triakis scyllium
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In teleost fishes, it is well-established that the gill serves as an important ionoregulatory organ in addition to its primary function of respiratory gas exchange. In elasmobranch fish, however, the ionoregulatory function of the gills is still poorly understood. Although mitochondria-rich (MR) cells have also been found in elasmobranch fish, these cells are considered to function primarily in acid-base regulation. In this study, we found a novel aggregate structure made up of cells with basolaterally-expressed Na+/K+-ATPase (NKA), in addition to NKA-immunoreactive MR cells that have already been described in the gill filament and lamella. The cell aggregates, named follicularly-arranged NKA-rich cells (follicular NRCs), were found exclusively in the epithelial lining of the venous web in the cavernous region of the filament and the inter-filamental space of the gill septum. The follicular NRCs form a single-layered follicular structure with a large lumen leading to the external environment. The follicular NRCs were characterized by: (i) well-developed microvilli on the apical membrane, (ii) less prominent infoldings of the basolateral membrane and (iii) typical junction structures including deep tight junction between cells. In addition, large numbers of vesicles were observed in the cytoplasm and some of them were fused to the lateral membrane. The follicular NRCs expressed Na+/H+ exchanger 3 and Ca2+ transporter 1. The follicular NRCs thus have the characteristics of absorptive ionoregulatory cells and this suggests that the elasmobranch gill probably contributes more importantly to body fluid homeostasis than previously thought.
KeywordsElasmobranch Gill Na+/K+-ATPase rich cell Follicular structure Ion regulation
We sincerely thank Prof. Christopher A Loretz of Univ. of Buffalo for critical reading of the manuscript and Dr. Soichi Watanabe of Univ. of Tokyo for his invaluable discussion and encouragement. This study was supported by Grants-in-Aid for Scientific Research to TK and SH.
- Braissant O, Wahli W (1998) A simplified in situ hybridization protocol using non-radioactively labeled probes to detect abundant and rare mRNAs on tissue sections. Biochem 1:10–16Google Scholar
- Burger JW (1965) Roles of the rectal gland and kidneys in salt and water excretion in the spiny dogfish. Physiol Zool 38:191–196Google Scholar
- Kaneko T, Watanabe S, Lee KM (2008) Functional morphology of mitochondrion-rich cells in euryhaline and stenohaline teleosts. Aqua BioSci Monogr 1:1–62Google Scholar
- Katoh F, Kaneko T (2003) Short-term transformation and longterm replacement of branchial chloride cells in killifish transferred from seawater to freshwater, revealed by morphofunctional observations and a newly established ‘time-differential double fluorescent staining’ technique. J Exp Biol 206:4113–4123PubMedCrossRefGoogle Scholar
- Piermarini PM, Verlander JW, Royaux IE, Evans DH (2002) Pendrin immunoreactivity in the gill epithelium of a euryhaline elasmobranch. Am J Physiol Regul Integr Comp Physio 283:R983–R992Google Scholar
- Tresguerres M, Parks SK, Wood CM, Goss GG (2007) V-H + -ATPase translocation during blood alkalosis in dogfish gills: interaction with carbonic anhydrase and involvement in the postfeeding alkaline tide. Am J Physiol 292:R2012–R2019Google Scholar