Ion transport in the intestine of Gobius niger in both isotonic and hypotonic conditions

Abstract

Ion transport in the intestine of Gobius niger, a euryhaline teleost, was studied in both isotonic and hypotonic conditions. Isolated tissues, mounted in Ussing chambers and bilaterally perfused with isotonic Ringer solution, developed a serosa negative transepithelial voltage and a short circuit current indicating a net negative current in absorptive direction. Bilateral removal of Cl À and Na þ from the bathing solutions as well as the luminal removal of K þ in the presence of Ba 2þ (10 À3 M) almost abolished both V t and I sc . Similar results were obtained by adding bumetanide (10 À5 M) to the luminal bath while other inhibitors of Cl À transport mechanisms were ineffective. These observations suggest that salt absorption begins with a coupled entry of Na þ , Cl À , and K þ across the apical membrane; a Ba 2þ inhibitable K þ conductance, demonstrated also by micropuncture experiments, recycles the ion into the lumen. Salt entry into the cell is driven by the operation of the basolateral Na þ /K þ -ATPase since serosal ouabain (10 À4 M) completely abolished both V t and I sc ; this pump also completes the Na þ absorption. The inhibitory effect of both serosal bumetanide (10 À4 M) and SITS (5?10 À4 M) suggests that Cl À would leave the cell via the KCl cotransport, the Cl/HCO 3 À antiport and/or conductive pathways. Bilateral exposure of tissues to hypotonic media produced a reduction of both the transepithelial voltage and the short circuit current probably due to the activation of homeostatic ionic fluxes involved in cell volume regulation. The results of experiments with both isolated enterocytes and intestine exposed to hypotonic solution suggested that the recovery of cell volume, after the initial cell swelling, involves a parallel opening of K þ and Cl À channels to facilitate net solute and water effluxes from the cell.

Influence of cell volume changes on protein synthesis in isolated hepatocytes of air-breathing walking catfish (Clarias batrachus)

“…Looking at the enormous importance of osmoregulation in fishes, some reports on this line are already available concerning the cell volume regulatory mechanism in red blood cells (Fugelli and Thoroed 1986;Motais et al 1991;Haynes and Goldstein 1993;Cossins et al 1994), renal cells (Kanli and Terreros 1997;Kanli and Norderhus 1998), intestinal cells (Lionetto et al 2001(Lionetto et al , 2002(Lionetto et al , 2005Trischitta et al 2004), and few reports in fish liver cells (Bianchini et al 1988;Ballatori and Boyer 1992;Fossat et al 1997;Espelt et al 2003). More recently, it has been demonstrated that the liver cells of air-breathing walking catfish (Clarias batrachus) possess an efficient volume regulatory mechanism, but remain in a partly swollen or shrunken state as long as they are exposed to anisotonicity (Goswami and Saha 2006).…”

Regulatory volume decrease and P receptor signaling in fish cells: mechanisms, physiology, and modeling approaches

“…Thus, the presence of voltage‐sensitive K + efflux, inhibited e.g. by BaCl 2 , was reported in goldfish renal proximal tubules (Terreros et al, '90), sea bass ( Dicentrarchus labrax ) gill cells (Duranton et al, 2000b), trout red cells (Egée et al, 2000), Gobius niger enterocytes (Trischitta et al, 2004), turbot hepatocytes (Ollivier et al, 2006c), and Gilthead sea bream hepatocytes (Faggio et al, 2011). In contrast, BaCl 2 was without effect on swelling‐induced K + fluxes in rainbow trout hepatocytes (Bianchini et al, '88) and brown trout ( Salmo trutta ) proximal renal tubules (Kanli and Norderhus, '98), indicating not only cell‐specific, but also species‐specific differences in the expression of the transporter.…”

“…In trout proximal renal tubule cells, volume recovery was similarly affected by the anion channel blocker MK‐196 but not by NPPB (Kanli and Norderhus, '98), whereas in turbot hepatocytes, NPPB and 9‐anthracene carboxylate (9‐AC) also inhibited up to 50% of RVD (Ollivier et al, 2006c). Almost complete inhibition of RVD by NPPB was observed in G. niger enterocytes (Trischitta et al, 2004) and in the rainbow trout hepatoma cell line RTH‐149 (Krumschnabel et al, 2007). These quantitative differences may not actually reflect different contributions of Cl − channels to RVD, as the concentrations at which the inhibitors were used differed between studies and concurrent inhibition of other transporters cannot be ruled out.…”

“…It was suggested that such a lack of RVD might be of importance for the maintenance of epithelial barrier function. However, intestinal preparations from G. niger (Trischitta et al, 2004) and eel (Lionetto et al, 2005) were capable of volume regulation, arguing against this. Similarly, we observed that goldfish hepatocytes do not display RVD in standard experimental settings, keeping their volume unregulated for at least 5 hr of exposure (Espelt et al, 2003).…”

Preliminary Study on the In vitro and In vivo Effects of Asparagopsis taxiformis Bioactive Phycoderivates on Teleosts

“…This regulatory response is called “regulatory volume decrease” (RVD). Volume-regulatory behavior has been observed in: cells isolated from digestive glands of Mytilus galloprovincialis (Torre et al, 2013), Gobius niger enterocytes (Trischitta et al, 2004), Anguilla anguilla enterocytes (Trischitta et al, 2005), turbot hepatocytes (Ollivier et al, 2006), Ehrlich ascites tumour cells (Hoffmann, 1984), and mammalian red blood cells (Ellory et al, 1985) exposed to osmotic stress.…”