AUTHOR=Lin Meng-Wei , Kuan Pou-Long , Sung Po-Hsuan , Tseng Yung-Che 

TITLE=Metabolic trade-offs associated with homeostatic adjustments in pelagic and benthic cephalopods: Comparative evaluations of NH4+/H+ transport machinery in gills

JOURNAL=Frontiers in Marine Science

VOLUME=9

YEAR=2022

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2022.971764

DOI=10.3389/fmars.2022.971764

ISSN=2296-7745

ABSTRACT=<p>Cephalopods are ancient mollusks that can be found in many different ecological niches in the ocean ranging from the intertidal zone to the deep-sea abyss. In order to adapt to a lifestyle in various habitats, cephalopods have evolved a variety of locomotory modes to accommodate their respective habitats. Most cephalopods have relatively high metabolic rates due to their less efficient swimming mode by jet propulsion. This lifestyle is characterized by a high level of energy expenditure, fueled exclusively by protein diets that are rapidly digested and may produce metabolic nitrogenous waste NH<sub>3</sub>/<inline-formula><mml:math display="inline" id="im1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mrow><mml:msubsup><mml:mrow><mml:mtext>NH</mml:mtext></mml:mrow><mml:mn>4</mml:mn><mml:mo> </mml:mo></mml:msubsup></mml:mrow><mml:mo>+</mml:mo></mml:msup></mml:mrow></mml:math></inline-formula>accumulation and acid-base disturbances. This study observed that the <inline-formula><mml:math display="inline" id="im2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mrow><mml:msubsup><mml:mrow><mml:mtext>NH</mml:mtext></mml:mrow><mml:mn>4</mml:mn><mml:mo> </mml:mo></mml:msubsup></mml:mrow><mml:mo>+</mml:mo></mml:msup></mml:mrow></mml:math></inline-formula>transport rate in pelagic bigfin reef squid <italic>(Sepioteuthis lessoniana)</italic> is two times faster than benthic common octopus (<italic>Octopus vulgaris</italic>). Inhibition of Na<sup>+</sup>/H<sup>+</sup> exchangers (NHEs) showed significant disruption of <inline-formula><mml:math display="inline" id="im3" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mrow><mml:msubsup><mml:mrow><mml:mtext>NH</mml:mtext></mml:mrow><mml:mn>4</mml:mn><mml:mo> </mml:mo></mml:msubsup></mml:mrow><mml:mo>+</mml:mo></mml:msup></mml:mrow></mml:math></inline-formula> and H<sup>+</sup> excretory processes in gills of octopus but not in squid. However, inhibition of vacuolar-type H<sup>+</sup>-ATPase (VHA) significantly disrupts <inline-formula><mml:math display="inline" id="im4" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mrow><mml:msubsup><mml:mrow><mml:mtext>NH</mml:mtext></mml:mrow><mml:mn>4</mml:mn><mml:mo> </mml:mo></mml:msubsup></mml:mrow><mml:mo>+</mml:mo></mml:msup></mml:mrow></mml:math></inline-formula> and H<sup>+</sup> transport rates in gills of both animals. Accordingly, for <inline-formula><mml:math display="inline" id="im5" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mrow><mml:msubsup><mml:mrow><mml:mtext>NH</mml:mtext></mml:mrow><mml:mn>4</mml:mn><mml:mo> </mml:mo></mml:msubsup></mml:mrow><mml:mo>+</mml:mo></mml:msup></mml:mrow></mml:math></inline-formula> and H<sup>+</sup> homeostasis, benthic octopus with lower aerobic respiration rates utilize both active and Na<sup>+</sup>-driven secondary transport machinery. In order to avoid <inline-formula><mml:math display="inline" id="im6" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mrow><mml:msubsup><mml:mrow><mml:mtext>NH</mml:mtext></mml:mrow><mml:mn>4</mml:mn><mml:mo> </mml:mo></mml:msubsup></mml:mrow><mml:mo>+</mml:mo></mml:msup></mml:mrow></mml:math></inline-formula> accumulated in the blood, pelagic squids with higher aerobic respiration rates prefer active <inline-formula><mml:math display="inline" id="im7" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mrow><mml:msubsup><mml:mrow><mml:mtext>NH</mml:mtext></mml:mrow><mml:mn>4</mml:mn><mml:mo> </mml:mo></mml:msubsup></mml:mrow><mml:mo>+</mml:mo></mml:msup></mml:mrow></mml:math></inline-formula> and H<sup>+</sup> transport mechanisms that consume ATP intensively.</p>