Regulation of Na+/K+-ATPase activity by nitric oxide in the kidney and gill of the brown trout (Salmo trutta)

Abstract

SUMMARYIn teleost fish, successful osmoregulation involves controlled ion transport mechanisms in kidney and gill epithelia. In this study, the effect of nitric oxide (NO) on Na+/K+-ATPase was investigated in vitro in these two tissues in brown trout (Salmo trutta)acclimated to freshwater. The NO donor sodium nitroprusside (SNP) inhibited in situ Na+/K+-ATPase activity, measured as ouabain-sensitive Rb+ uptake, in both samples of kidney and gill tissue and in isolated gill cells. The effect was dose-dependent in both tissues, with a maximal observed inhibition of approximately 40–50% (1 mmol l –1 SNP). The time-course of inhibition revealed a maximum effect with 10 min pre-incubation. The effect of SNP was reproduced with another NO donor, papa-nonoate (NOC-15; 200 μmol l–1), and was prevented by the NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO; 1 mmol l–1). To further investigate the mechanism of the NO effect,whole-tissue Na+ and K+ levels were analysed. In kidney,SNP (1 mmol l–1) led to an increase in tissue Na+levels and a decrease in K+ levels in a 3:2 ratio. In gill tissue,no change in either ion was observed. These observations indicate that the effect on Na+/K+-ATPase is direct rather than due to a decrease in intracellular Na+, its rate-limiting substrate. SNP elevated the level of cyclic GMP (cGMP) in both kidney and gill tissue. Dibutyryl cyclic GMP (db-cGMP; 1 mmol l–1) also inhibited Na+/K+-ATPase activity in both tissues. Hence, a possible mechanism may involve the cGMP-activated kinase, even though other mechanisms cannot be excluded.

Neuroendocrine control of ionic balance in zebrafish

“…Increasing evidence suggests that gasotransmitters may play a role in osmoregulation in fish (Ebbesson et al, 2005;Kumai et al, 2014c;Kwong and Perry, 2015b;Tipsmark and Madsen, 2003). To date, only the role of H 2 S in ionic regulation has been investigated in zebrafish.…”

Metabolic fates and effects of nitrite in brown trout under normoxic and hypoxic conditions: blood and tissue nitrite metabolism and interactions with branchialNOS,Na+/K+-ATPaseandhsp70expression

“…On the basis of a reported inhibitory effect of NO on gill NKA activity (Tipsmark and Madsen, 2003;Ebbesson et al, 2005) and the formation of NO from nitrite, particularly under hypoxic conditions, we anticipated that nitrite exposure would inhibit branchial NKA activity. Hypoxia per se can also decrease gill NKA activity in fish (Richards et al, 2007;Wood et al, 2007;Lundgreen et al, 2008;Hansen and Jensen, 2010).…”

“…We also tested specific new hypotheses that relate to the NO-generating power of nitrite. Thus, NO has been shown to inhibit branchial Na + /K + -ATPase (NKA) activity in brown trout (Tipsmark and Madsen, 2003), and we predicted that nitrite would exert a similar inhibition, and that this would become reflected in a reduced branchial NKA activity and increased nka mRNA expression. We also hypothesized the existence of crosstalk between nitrite and the NOS reaction, so that nitrite -as a natural product of the NOS reaction -exerts a negative-feedback inhibition on NOS gene expression.…”

Differential regulation of cystic fibrosis transmembrane conductance regulator and Na+,K+-ATPase in gills of striped bass, Morone saxatilis: effect of salinity and hormones

“…Experiment 4: effect of EGF in vitro on ERK 1/2 activity Gill cells from FW-acclimated fish were prepared as described in Tipsmark & Madsen (2003) modified from Verbost et al (1994). They were transferred to 96-well plates and allowed to settle in Ringer's solution (see above) for 20 min at room temperature.…”