Comparison of Cl⁻‐absorption in the intestine of the seawater‐ and freshwater‐adapted eel, Anguilla anguilla: Evidence for the presence of an Na‐K‐Cl cotransport system on the luminal membrane of the enterocyte

Abstract

The mechanism(s1 of absorption of chloride ions (C1-absorption), as measured by the short-circuit current (I,,, pA-cm ' 1, was investigated in the intestinal middle part of the seawater-(SW) and the freshwater-(FW) adapted eel. Tissues, mounted in an Ussing chamber and continuously perfused by gravity flow on both sides with 20 mM HCOB -1% C 0 2 Ringer's solution at pH 8.0, developed a serosa-negative transepithelial voltage (V,, mV) and an I,, that were both lower in FW-adapted than in SW-adapted eels. Bilateral removal of Na+ or C1-from the bathing solutions reduced both electrical variables to zero. Removal of K + from or addition of Ba'' (1 mM) to the luminal bath markedly decreased I,, and V,. When a K'-free plus Ba2+-containing solution perfused the lumen, I,, and V, were almost completely abolished. Luminal bumetanide (10 MI, an inhibitor of Na+-K + -2C1-cotransport, reduced I,, and V, by about 90% in a few minutes. M) and DIDS (4,4'-diisothiocyanostilbene-2,2-disulphonic acid; 10 -4 M), inhibitors of Na+/H+ and C1-/HC03-exchangers, and hydrochlorothiazide (lop4 M), an inhibitor of the Na-Cl symport, had no effect on I,, and V, when added luminally. Serosal ouabain M) abolished I,, and V, in about 30 min. All the above experimental manoeuvres led to similar results in both SW-adapted and FW-adapted eels.The data suggest that in the intestine of both SW and FW eels, Cl--absorption is mediated by a luminally located neutral Na Amiloride (

Hypotonicity induced K+ and anion conductive pathways activation in eel intestinal epithelium

“…-cotransporter (Trischitta et al, 1992a), and that external hypertonicity increases V te and I sc by stimulation of the triporter (Lionetto et al, 2001). The possibility that the observed decrease of V te and I sc induced by hypotonicity might be the result of an inhibition of the luminal Na following their conductance changes.…”

“…-transporter system (Trischitta et al, 1992a;Marvão et al, 1994). Marvão et al (1994), using conventional and selective microelectrodes, also found a Ba 2+ -inhibitable K + conductance on the basolateral membrane.…”

Molecular Characterization and Expression Pattern of Na⁺-K⁺-2Cl^- Cotransporter 2 (NKCC2) in the Intestine of Starry Flounder Platichthys stellatus after Bacterial Challenge

“…Piscine NKCC has been suggested to be involved in intestinal salt absorption in several fish species, including European eel, Anguilla anguilla, and Mozambique tilapia, Oreochromis mossambicus (Musch et al, 1982;Trischitta et al, 1992;Li et al, 2014). In addition, a duplicated pair of NKCC2 isoforms (NKCC2α and NKCC2β) has been identified in several teleosts, and they are expressed in different tissues and organs (Cutler and Cramb, 2008;Hiroi et al, 2008;Watanabe et al, 2011).…”

Changes in the electrophysiological parameters of the posterior intestine of Anguilla anguilla (Pisces) induced by oxytocin, urotensin II and aldosterone

“…However, Na + -K + -ATPase and the coupled Na + -K + -Cl -transport, observed in the intestine of seawater-adapted A. anguilla, were also demonstrable in the intestine of freshwateradapted eels (2,3). In addition, Trischitta et al (2) showed that adaptation to seawater or freshwater does not alter the basic transport properties of the intestine of A. anguilla, and proposed that even in freshwater-adapted fishes this organ could complement the function of the gills in the maintenance of the internal ionic composition. The pattern of stabilization of the transepithelial potential difference of the intestine of this species also suggests that this organ may quickly lead to greater animal adaptation to sea-or freshwater, which is important for the catadromous life of A. anguilla (3).…”

“…Transepithelial potential difference (TPD), short-circuit current (SCC) and conductance (G) were measured in the stripped posterior intestine of A. anguilla as previously described by Baldisserotto and Mimura (3). The physiological control solution contained 118.5 mM NaCl, 25.0 mM NaHCO 3 , 3.0 mM CaCl 2 .2H 2 O, 4.7 mM KCl, 1.0 mM MgCl 2 .6H 2 O, 5.0 mM D-glucose, and 10.0 mM D-mannitol, pH 7.8, and was gassed with 98% O 2 -2% CO 2 .…”