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Figure 9 | Frontiers in Zoology

Figure 9

From: Branchial NH4+-dependent acid–base transport mechanisms and energy metabolism of squid (Sepioteuthis lessoniana) affected by seawater acidification

Figure 9

Hypothetical model for the coupling of acid–base regulation and gas exchange in the squid gill. Schematic illustration of the inner (ion-transporting) and the outer (respiratory) epithelium connected by pillar cells. Ionocytes of the ion-transporting epithelium express Na+/K+-ATPase (NKA), V-type H+-ATPase (HA), Na+/H+ exchanger 3 (NHE3), Rhesus protein (RhP) and Na+/HCO3 co-transporter (NBC) which are involved in HCO3 buffering and NH4+ excretion. NH4+ is trapped in the acidified tubular space of the 3° gill lamellae whereas the outer respiratory epithelium is spatially separated from the excretory epithelium. HA expressed in pillar cells may contribute to blood pH homeostasis to support gas transport by the highly pH sensitive hemocyanin (HC).

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