Intracellular pH regulation in rainbow trout (Oncorhynchus mykiss) hepatocytes: the activity of sodium/proton exchange is oxygen-dependent

Tuominen, Aulis; Rissanen, Eeva; Bogdanova, Anna; Nikinmaa, Mikko

doi:10.1007/s00360-003-0336-x

Cited by 10 publications

(11 citation statements)

References 35 publications

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“…This observation makes it tempting to suggest that this radical species is the second messenger involved in transferring information from so far unknown primary oxygen-binding protein(s) to ion transporters. Notably, treatment of hepatocytes with MPG suppresses proton extrusion mediated by Na + /H + exchanger (Tuominen et al, 2003). The latter finding suggests common regulatory pathways for oxygen-induced regulation of both ion transporters.…”

Section: Discussionmentioning

confidence: 79%

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Hypoxic responses of Na+/K+ ATPase in trout hepatocytes

Bogdanova

Grenacher

Nikinmaa

et al. 2005

Journal of Experimental Biology

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SUMMARY Reduction in oxygenation induces inhibition of Na+/K+ATPase in a number of cells and tissues, including hepatocytes. When not reversed, decrease in Na+/K+ pump activity leads to a gradual Na+ accumulation, cell swelling and death. However, when accompanied by suppression of dissipative cation pathways, it has also been shown to be a beneficial adaptive strategy used by some hypoxia-tolerant species to reduce ATP consumption during prolonged periods of anoxia. This study aims to investigate acute hypoxic responses of the Na+/K+ ATPase in primary cultures of trout hepatocytes. Gradual decrease in oxygenation was followed by an instantaneous transient dose-dependent downregulation of the Na+/K+ ATPase transport activity, but was without an effect on hydrolytic function of the enzyme. Hypoxia-induced inhibition of active K+ influx was reversed spontaneously when hypoxic incubation time exceeded 20 min. The stimulating effect of prolonged hypoxic exposure on the Na+/K+ pump is most probably secondary to hypoxia-induced activation of the Na+/H+ exchanger with the following Na+accumulation leading to Na+/K+ ATPase activation. Hypoxia-induced inhibition of the Na+/K+ pump was not caused by ATP depletion or global oxidative stress. However, local controlled production of reactive oxygen species seems to play an important role in hypoxia-induced regulation of the Na+/K+ ATPase. Treatment of cells with mercaptopropionyl glycine (MPG), a scavenger of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{O}\mathrm{H}^{.-}\) \end{document}, abolished hypoxia-induced inhibition of the Na+/K+ ATPase. Earlier on we have shown that activation of Na+/H+ exchanger under hypoxic conditions can be opposed by MPG treatment as well. Taken together our results suggest that regulation of both oxygen-sensitive transporters may be accomplished by local changes in free radical production.

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Section: Discussionmentioning

confidence: 79%

“…Data we have obtained previously on oxygen sensitivity of Na + /H + exchanger reveal that this transporter is activated by hypoxic treatment (Tuominen et al, 2003). If this were the case, hypoxic conditions should result in gradual Na + accumulation as passive Na + uptake is increased and active efflux downregulated.…”

Section: Discussionmentioning

confidence: 90%

Hypoxic responses of Na+/K+ ATPase in trout hepatocytes

Bogdanova

Grenacher

Nikinmaa

et al. 2005

Journal of Experimental Biology

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“…To further substantiate our conclusion on the dependence of Na ϩ /H ϩ exchange activity on an intact actin-based cytoskeleton, we also investigated the impact of CB on pH i recovery following an acid load, which, as shown in previous studies on trout hepatocytes (23,60,63), is to a major extent dependent on Na ϩ /H ϩ exchange and, to a minor extent, on a SITSsensitive anion transporter. We observed that upon acidification after an NH 4 ϩ prepulse in the presence of SITS, control cells clearly recovered pH i , whereas in CB-treated cells, no such recovery was noted.…”

Section: Discussionmentioning

confidence: 84%

“…The Prompted by our findings on proton secretion rates, we suspected that these different pH i response patterns could have been caused by an effect of cytoskeletal disruption on the Na ϩ /H ϩ exchanger. To investigate this possibility, we examined the pH i recovery in controls and CB-treated hepatocytes after the induction of an acid load, a condition known to strongly activate this ion transporter in trout hepatocytes (23,60,63). Intracellular acidification was achieved using the NH 4 ϩ prepulse technique (8,47) with concurrent addition of the inhibitor of Na ϩ -dependent Cl Ϫ /HCO 3 Ϫ exchange, SITS, to prevent compensatory activation of this transporter should Na ϩ /H ϩ exchange indeed have been diminished by the CB treatment.…”

Section: Effect Of Cytoskeleton Disrupting Agents On F-actin and Tubumentioning

confidence: 99%

Importance of cytoskeletal elements in volume regulatory responses of trout hepatocytes

Ebner¹,

Cordas²,

Pafundo³

et al. 2005

American Journal of Physiology-Regulatory, Integrative and Comp

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The role of cytoskeletal elements in volume regulation was studied in trout hepatocytes by investigating changes in F-actin distribution during anisotonic exposure and assessing the impact of cytoskeleton disruption on volume regulatory responses. Hypotonic challenge caused a significant decrease in the ratio of cortical to cytoplasmic F-actin, whereas this ratio was unaffected in hypertonic saline. Disruption of microfilaments with cytochalasin B (CB) or cytochalasin D significantly slowed volume recovery following hypo- and hypertonic exposure in both attached and suspended cells. The decrease of net proton release and the intracellular acidification elicited by hypotonicity were unaltered by CB, whereas the increase of proton release in hypertonic saline was dramatically reduced. Because amiloride almost completely blocked the hypertonic increase of proton release and cytoskeleton disruption diminished the associated increase of intracellular pH (pH(i)), we suggest that F-actin disruption affected Na(+)/H(+) exchanger activity. In line with this, pH(i) recovery after an ammonium prepulse was significantly inhibited in CB-treated cells. The increase of cytosolic Na(+) under hypertonic conditions was not diminished but, rather, enhanced by F-actin disruption, presumably due to inhibited Na(+)-K(+)-ATPase activity and stimulated Na(+) channel activity. The elevation of cytosolic Ca(2+) in hypertonic medium was significantly reduced by CB. Altogether, our results indicate that the F-actin network is of crucial importance in the cellular responses to anisotonic conditions, possibly via interaction with the activity of ion transporters and with signalling cascades responsible for their activation. Disruption of microtubules with colchicine had no effect on any of the parameters investigated.

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“…rainbow trout hepatocytes have both NHE and Na ϩ /HCO 3 Ϫ cotransporters that contribute to pHi regulation during acid loading (18). In addition, NHE activity is higher at low O 2 levels, suggesting a role in correcting for anoxia-induced acidosis (54). On the other hand, in hepatocytes isolated from goldfish (Carassius auratus), a far more anoxia-tolerant fish, a sodium-independent Cl Ϫ /HCO 3 Ϫ exchanger was experimentally determined to increase acid excretion during chemical anoxia, implying that this pH regulatory mechanism may be contributing to hypoxia tolerance (29).…”

Section: Discussionmentioning

confidence: 99%

Complete intracellular pH protection during extracellular pH depression is associated with hypercarbia tolerance in white sturgeon,Acipenser transmontanus

Baker

Matey²,

Huynh³

et al. 2009

American Journal of Physiology-Regulatory, Integrative and Comp

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Baker DW, Matey V, Huynh KT, Wilson JM, Morgan JD, Brauner CJ. Complete intracellular pH protection during extracellular pH depression is associated with hypercarbia tolerance in white sturgeon, Acipenser transmontanus. Am J Physiol Regul Integr Comp Physiol 296: R1868 -R1880, 2009. First published April 1, 2009 doi:10.1152/ajpregu.90767.2008.-Sturgeons are among the most CO 2 tolerant of fishes investigated to date. However, the basis of this exceptional CO 2 tolerance is unknown. Here, white sturgeon, Acipenser transmontanus, were exposed to elevated CO 2 to investigate the mechanisms associated with short-term hypercarbia tolerance. During exposure to 1.5 kPa PCO 2, transient blood pH [extracellular pH (pHe)] depression was compensated within 24 h and associated with net plasma HCO 3 Ϫ accumulation and equimolar Cl Ϫ loss, and changes in gill morphology, such as a decrease in apical surface area of mitochondrial-rich cells. These findings indicate that pHe recovery at this level of hypercarbia is accomplished in a manner similar to most freshwater teleost species studied to date, although branchial mechanisms involved may differ. White sturgeon exposed to more severe hypercarbia (3 and 6 kPa PCO 2) for 48 h exhibited incomplete pH compensation in blood and red blood cells. Despite pHe depression, intracellular pH (pHi) of white muscle, heart, brain, and liver did not decrease during a transient (6 h of 1.5 kPa PCO 2 ) or prolonged (48 h at 3 and 6 kPa PCO 2) blood acidosis. This pHi protection was not due to high intrinsic buffering in tissues. Such tight active cellular regulation of pHi in the absence of pHe compensation represents a unique pattern for non-air-breathing fishes, and we hypothesize that it is the basis for the exceptional CO 2 tolerance of white sturgeon and, likely, other CO 2 tolerant fishes. Further research to elucidate the specific mechanisms responsible for this tremendous pH regulatory capacity in tissues of white sturgeon is warranted. sturgeon; acid-base regulation; intracellular pH; CO 2 tolerance; hypercarbia/hypercapnia AQUATIC HYPERCARBIA (elevated PCO 2 in water) occurs in fresh and estuarine systems, and Pw CO 2 levels as great as 8 kPa (20-to 30-fold increase over the resting arterial Pa CO 2 of fish) have been observed (24,55) (16)] changes at the gill. These changes in branchial morphology and acid-base-relevant ion transporters may aid with the net acid secretion or base absorption mechanisms necessary to promote blood pH compensation (16,20), although direct evidence for this is lacking.Changes in intracellular pH (pHi) in most fish species studied to date are qualitatively similar to, albeit smaller than, blood pH changes during a respiratory acidosis (6, 49). Because function of many cellular components, such as enzyme activity, is pH sensitive, a general acidosis may have severe consequences on cellular processes, including metabolic energy production (25, 50). Only a handful of studies have measured pHi and pHe simultaneously during hypercarbia in fish; these studies...

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Intracellular pH regulation in rainbow trout (Oncorhynchus mykiss) hepatocytes: the activity of sodium/proton exchange is oxygen-dependent

Cited by 10 publications

References 35 publications

Hypoxic responses of Na+/K+ ATPase in trout hepatocytes

Hypoxic responses of Na+/K+ ATPase in trout hepatocytes

Importance of cytoskeletal elements in volume regulatory responses of trout hepatocytes

Complete intracellular pH protection during extracellular pH depression is associated with hypercarbia tolerance in white sturgeon,Acipenser transmontanus

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