AUTHOR=Hu Marian Y. , Sung Po-Hsuan , Guh Ying-Jey , Lee Jay-Ron , Hwang Pung-Pung , Weihrauch Dirk , Tseng Yung-Che 

TITLE=Perfused Gills Reveal Fundamental Principles of pH Regulation and Ammonia Homeostasis in the Cephalopod Octopus vulgaris

JOURNAL=Frontiers in Physiology

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2017.00162

DOI=10.3389/fphys.2017.00162

ISSN=1664-042X

ABSTRACT=<p>In contrast to terrestrial animals most aquatic species can be characterized by relatively higher blood <inline-formula><mml:math id="M1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msubsup><mml:mtext>NH</mml:mtext><mml:mn>4</mml:mn><mml:mo>+</mml:mo></mml:msubsup></mml:mrow></mml:math></inline-formula> concentrations despite its potential toxicity to the central nervous system. Although many aquatic species excrete <inline-formula><mml:math id="M2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msubsup><mml:mtext>NH</mml:mtext><mml:mn>4</mml:mn><mml:mo>+</mml:mo></mml:msubsup></mml:mrow></mml:math></inline-formula> via specialized epithelia little information is available regarding the mechanistic basis for NH<sub>3</sub>/<inline-formula><mml:math id="M3" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msubsup><mml:mtext>NH</mml:mtext><mml:mn>4</mml:mn><mml:mo>+</mml:mo></mml:msubsup></mml:mrow></mml:math></inline-formula> homeostasis in molluscs. Using perfused gills of <italic>Octopus vulgaris</italic> we studied acid-base regulation and ammonia excretion pathways in this cephalopod species. The octopus gill is capable of regulating ammonia (NH<sub>3</sub>/<inline-formula><mml:math id="M4" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msubsup><mml:mtext>NH</mml:mtext><mml:mn>4</mml:mn><mml:mo>+</mml:mo></mml:msubsup></mml:mrow></mml:math></inline-formula>) homeostasis by the accumulation of ammonia at low blood levels (&lt;260 μM) and secretion at blood ammonia concentrations exceeding <italic>in vivo</italic> levels of 300 μM. <inline-formula><mml:math id="M5" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msubsup><mml:mtext>NH</mml:mtext><mml:mn>4</mml:mn><mml:mo>+</mml:mo></mml:msubsup></mml:mrow></mml:math></inline-formula> transport is sensitive to the adenylyl cyclase inhibitor KH7 indicating that this process is mediated through cAMP-dependent pathways. The perfused octopus gill has substantial pH regulatory abilities during an acidosis, accompanied by an increased secretion of <inline-formula><mml:math id="M6" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msubsup><mml:mtext>NH</mml:mtext><mml:mn>4</mml:mn><mml:mo>+</mml:mo></mml:msubsup></mml:mrow></mml:math></inline-formula>. Immunohistochemical and qPCR analyses revealed tissue specific expression and localization of Na<sup>+</sup>/K<sup>+</sup>-ATPase, V-type H<sup>+</sup>-ATPase, Na<sup>+</sup>/H<sup>+</sup>-exchanger 3, and Rhesus protein in the gill. Using the octopus gill as a molluscan model, our results highlight the coupling of acid-base regulation and nitrogen excretion, which may represent a conserved pH regulatory mechanism across many marine taxa.</p>