Open‐circuit sodium and chloride fluxes across isolated opercular epithelia from the teleost Fundulus heteroclitus.

Abstract

2. The mean predicted Na+ flux ratio was 0-94 + 0-08 and the observed ratio was 1-14+0-12 (n = 15; mean+s.E. of mean). The difference in these means was not significant (P > 0-20). The mean predicted Cl-flux ratio was 11-4 + 0-9 and the mean observed ratio was 1-38 + 0-27 (n = 10). The difference in these means was significant (P < 0-001).3. Ouabain, at 10-6 M in the serosal solution, produced a significant (P < 0-01) reduction in the Na+ efflux while having no significant (P > 0-40) effect on the Na+ influx. The agreement between the predicted (1.70 + 0-14) and observed (1-72 + 0-18) Na+ flux ratios after ouabain treatment suggested that this effect could be completely attributed to the depolarization of the epithelium secondary to ATPase inhibition. 4. fl-adrenergic activation by isoprenaline stimulated the Cl-efflux 24-2 % and ot-adrenergic activation by noradrenaline inhibited the Cl-efflux 66-5 %. These changes occurred oppositely to those predicted by the changes in the electrical gradient produced by these agents, while the changes in the Cl-influxes corresponded to the electrical changes. Short-circuit experiments confirmed these effects on the Cl-efflux and the lack of effects on the Cl-influx.5. The results suggested that Na+ was near thermodynamic equilibrium and that the unidirectional fluxes were passive. The effects of a-and /i-adrenergic activation suggested that the active Cl-secretion may be antagonistically regulated by catecholamines.

Passive sodium movements across the opercular epithelium: The paracellular shunt pathway and ionic conductance

“…It appeared then, that the opercular epithelium was not strictly "leaky", could vary its ionic permeability in vitro, similar to the intact fish, and could possibly exhibit an amiloride sensitivity. Additional evidence against transcellular Na § movements is the lack of a direct effect of ouabain on the unidirectional Na + fluxes across the operculum Degnan & Zadunaisky, 1979).…”

“…The effect of a variety of compounds, including TAP, on the transcellular C1-efflux while having no effect on the CI-influx Degnan & Zadunaisky, 1979), can be taken as evidence favoring an extracellular CIinflux. In the operculum, TAP had no effect on the…”

Gene expression after freshwater transfer in gills and opercular epithelia of killifish: insight into divergent mechanisms of ion transport

“…In contrast, when the opercular epithelium of freshwater-acclimated killifish is mounted in vitro with freshwater on the apical surface, it absorbs Cl -actively at low rates and Na + uptake is passive Burgess et al, 1998). Only 1% of Na + and Cl -transport in the intact animal is accomplished by the opercular epithelium (Degnan and Zadunaisky, 1979) Patrick and Wood, 1999;Edwards et al, 2005). Some other genes thought to be important in freshwater fish gills, such as carbonic anhydrase (CA) and Na + ,HCO 3 -cotransporter (NBC), may also be involved (Wood and Pärt, 2000;Marshall, 2002;Perry et al, 2003a,b).…”

Sodium dependency of active chloride transport across isolated fish skin (Gillichthys mirabilis).

“…The results show clearly that the active secretion of Cl-by chloride cells depends upon Na,K-ATPase; previous in vivo studies with eels suggested that extra-renal Na+ and Cl-excretion are inhibited by ouabain, but the injection of this cardiac glycoside could reduce the physiological surface area of the gill as a result of the inhibition of cardiac activity (Silva, Solomon, Spokes & Epstein, 1977). Ouabain decreases net Na+ transport by the Fundulus opercular epithelium at open circuit (Degnan & Zadunaisky, 1979), apparently as a result ofreduced transepithelial potential, because there is no net Na+ transport by the opercular epithelium or Gillichthys skin when these tissues are clamped to zero mV (Degnan et al 1977;Marshall & Bern, 1980). Both ouabain and Na-free Ringer solution reduced net Cl-flux as a result of decreased efflux and increased influx.…”