Active NaCl absorption across posterior gills of hyperosmoregulatingChasmagnathus granulatus

Abstract

SUMMARYSplit lamellae of posterior gills of Chasmagnathus granulatusadapted to 2.5‰ salinity were mounted in a modified Ussing chamber. With NaCl-saline on both sides of the preparation a transepithelial voltage(Vte) of 4.1±0.5 mV (outside positive) was measured. After voltage-clamping, the negative short-circuit current(Isc) amounted to -142±21 μA cm-2 at a conductance (Gte) of 44±5 mS cm-2. Substitution of either chloride (by nitrate) or sodium (by choline) on both sides of split gill lamellae significantly reduced Isc (by 70-80%) and Gte (by 30-50%). External CsCl (but not BaCl2 or furosemide) inhibited the negative Isc without affecting Gte. Addition of ouabain, BaCl2 or diphenylamine-2-carboxylate to the internal bath inhibited Isc at unchanged Gte. Internal acetazolamide did not affect Isc or Gte across split gill lamellae. Unidirectional Na+ influx across isolated and perfused posterior gills, however, was reduced by internal acetazolamide by approximately 20% at constant Vte. The results suggest that posterior gills of hyperosmoregulating C. granulatus display a high conductance epithelium that actively absorbs NaCl in a coupled way by an electrogenic mechanism similar to that seen in the thick ascending limb of Henle's loop and, to a minor degree, by an electroneutral mechanism,presumably via apical Na+/H+- and Cl-/HCO3--antiports.

The role of an ancestral hyperpolarization activated cyclic nucleotide-gated K+-channel in branchial acid-base regulation in the green crab,Carcinus maenas(L.)

“…Each perfusion step allowed for 10 min adjustment of the gill, after which the perfusate was collected for 30 min. To block basolateral K + channels, BaCl 2 was applied basolaterally in the second perfusion step at a concentration of 12 mmol l −1 (Schirmanns and Zeiske, 1994;Riestenpatt, 1995;Riestenpatt et al, 1996;Onken et al, 2003). The inhibitor ZD7288 (4-ethylphenylamino-1,2-dimethyl-6-methylaminopyrimidinium Table 1.…”

“…8). In studies to date, the presence of K + channels in the gill epithelium of decapod crustaceans has only been verified by ion flux and shortcircuit current studies on split gill lamellae applying the inhibitors Ba 2+ and Cs + (Onken et al, 1991(Onken et al, , 2003Riestenpatt et al, 1996;Weihrauch et al, 1998Weihrauch et al, , 1999. Because of its similar radius in comparison to K + , Ba 2+ is able to enter the channel pore and bind to the selection filter motif (SF4) domain of the respective K + channels, thereby competing with K + and blocking its binding site more potently because of its dual positive charge (Rossi et al, 2013).…”

“…In the crustacean gill epithelium, K + channels have been identified to participate in the establishment of an electrochemical gradient over the basolateral membrane mainly generated by a basolateral Na + /K + -ATPase (Onken et al, 1991;Riestenpatt et al, 1996). Furthermore, apical K + channels seem to co-localize with apical Na + /K + /2Cl − (NKCC) to allow K + circulation and thereby an uptake of Na + and Cl − in crustaceans (Riestenpatt et al, 1996;Onken et al, 2003). Because of the presence of apical NKCC and apical K + channels, as well as the accompanying basolateral Cl − channel, the moderately leaky gill epithelium of C. maenas has been compared with the thick ascending limb (TAL) of the mammalian kidney (Riestenpatt et al, 1996).…”

“…BaCl 2 altered I SC without affecting the conductance, but had no effect when applied apically even though apical Cs + , another unspecific K + channel blocker, resulted in a significant decrease of I SC (Onken et al, 2003). At these relatively high concentrations, Ba 2+ is believed to target voltage-gated/delayed-rectifier K + channels (Rudy, 1988;Wollmuth, 1994), while specifically inhibiting Ca…”

The effects of hypoxia on active ionic transport processes in the gill epithelium of hyperregulating crab, Carcinus maneas

“…Application of the electrophysiological Isc method in transport studies on Carcinus gill hemilamella has shown that inward movement of Cl − is mediated by Na + /K + /2Cl − cotransport (Riestenpatt et al, 1996;Onken et al, 2003;Lucu and Towle, 2010). The main generator of this coupled transport is the basolaterally located Na + , K + -ATPase, because specific inhibition of Na + , K + -ATPase by applying ouabain to the basolateral side of the posterior Carcinus gills inhibits the Isc (Siebers et al, 1985;Onken and Siebers, 1992;Riestenpatt et al, 1996;Lucu and Flik, 1999).…”