Carbonic anhydrase expression in the branchial ionocytes of rainbow trout

Abstract

Rainbow trout () exposed to acid-base challenges activate branchial mechanisms for the excretion of acid-base equivalents. Current models of branchial acid-base excretion in freshwater rainbow trout propose two main ionocyte types: the peanut lectin agglutinin-positive (PNA) mitochondrion-rich cell or ionocyte is believed to secrete HCO in exchange for Cl, whereas H secretion is thought to occur across PNA ionocytes in exchange for Na Both HCO and H are supplied by intracellular hydration of CO catalysed by cytosolic carbonic anhydrase (CAc). Immunohistochemical approaches revealed that under control conditions, CAc was detectable in 92.3±1.0% (=11) of PNA ionocytes, and the abundance of PNA ionocytes increased in response to systemic acidosis elicited by 72 h exposure to water of low pH (nominally pH 4.5), hypercapnia (1% CO, nominally 7.6 Torr) or hyperoxia (achieved by gassing water with pure O), as did the abundance of PNA ionocytes that exhibited immunofluorescence for CAc. However, just 4.3±0.6% (=11) of PNA ionocytes expressed detectable CAc under control conditions. Marked increases in the abundance of CAc-positive PNA ionocytes were detected following exposure of trout to a base load via recovery from hypercapnia or base infusion (72 h infusion with 140 mmol l NaHCO). The percentage of CAc-positive PNA ionocytes also was increased in trout treated with cortisol (10 mg kg hydrocortisone 21-hemisuccinate daily for 7 days). These results suggest that regulation of CA within PNA ionocytes and/or the abundance of CAc-positive PNA ionocytes plays a role in activating base secretion in response to systemic alkalosis.

Specific immunity proteomic profile of the skin mucus of Antarctic fish Chionodraco hamatus and Notothenia coriiceps

“…Considering AFP-IV was related to antioxidative, anti-inflammatory and antibacterial functions (Mao et al, 2018), and it upregulated in C. hamatus, the AFP-IV may play an important role in the C. hamatus immune system. Furthermore, in the "response to stress" GO group (Table .1), the presence of MnSOD and hspe1 has been reported to play an important role in antioxidant status, inflammation, transformation and other normal cellular functions (Brannen & Gilmour, 2018;Hatzel et al, 2015;Qin et al, 2020). The protein KRT8 was upregulated in the skin mucus of gilthead sea bream (Sparus aurata), and after chronic exposure to low temperatures many fragments or cleaved proteins presented as keratin forms were detected.…”

Conflict and Compromise: Using Reversible Remodeling to Manage Competing Physiological Demands at the Fish Gill

“…The Amazonian oscar, for example, does not appear to cover and uncover its gill lamellae with an ILCM, but exposure to hypoxia induces a different type of reversible morphological plasticity of the gill epithelium, in which pavement cells cover ionocytes (36,74). Similarly, rainbow trout (Oncorhynchus mykiss) do not develop an ILCM in response to elevated ammonia (62) or high salinity ( 2), yet this species shows changes in ionocyte abundance and covering of ionocytes by pavement cells in response to acid-base or osmotic challenges (6,24,27,51). Indeed, morphological plasticity of the gill epithelium in response to acid-base (the "morphological model" of acid-base regulation) or osmotic challenges has been documented in a range of fish species (25,26,29,53).…”