Format

Send to

Choose Destination
J Exp Biol. 2015 Apr 15;218(Pt 8):1259-69. doi: 10.1242/jeb.117317. Epub 2015 Mar 6.

Paracellular pathway remodeling enhances sodium secretion by teleost fish in hypersaline environments.

Author information

1
Department of Biology, St Francis Xavier University, J. Bruce Brown Hall, Room 214, 2320 Notre Dame Avenue, Antigonish, Nova Scotia, Canada B2G 2W5.
2
Department of Biology, St Francis Xavier University, J. Bruce Brown Hall, Room 214, 2320 Notre Dame Avenue, Antigonish, Nova Scotia, Canada B2G 2W5 bmarshal@stfx.ca.

Abstract

In vertebrate salt-secreting epithelia, Na(+) moves passively down an electrochemical gradient via a paracellular pathway. We assessed how this pathway is modified to allow Na(+) secretion in hypersaline environments. Mummichogs (Fundulus heteroclitus) acclimated to hypersaline [2× seawater (2SW), 64‰] for 30 days developed invasive projections of accessory cells with an increased area of tight junctions, detected by punctate distribution of CFTR (cystic fibrosis transmembrane conductance regulator) immunofluorescence and transmission electron miscroscopy of the opercular epithelia, which form a gill-like tissue rich in ionocytes. Distribution of CFTR was not explained by membrane raft organization, because chlorpromazine (50 μmol l(-1)) and filipin (1.5 μmol l(-1)) did not affect opercular epithelia electrophysiology. Isolated opercular epithelia bathed in SW on the mucosal side had a transepithelial potential (Vt) of +40.1±0.9 mV (N=24), sufficient for passive Na(+) secretion (Nernst equilibrium voltage≡ENa=+24.11 mV). Opercular epithelia from fish acclimated to 2SW and bathed in 2SW had higher Vt of +45.1±1.2 mV (N=24), sufficient for passive Na(+) secretion (ENa=+40.74 mV), but with diminished net driving force. Bumetanide block of Cl(-) secretion reduced Vt by 45% and 29% in SW and 2SW, respectively, a decrease in the driving force for Na(+) extrusion. Estimates of shunt conductance from epithelial conductance (Gt) versus short-circuit current (Isc) plots (extrapolation to zero Isc) suggested a reduction in total epithelial shunt conductance in 2SW-acclimated fish. In contrast, the morphological elaboration of tight junctions, leading to an increase in accessory-cell-ionocyte contact points, suggests an increase in local paracellular conductance, compensating for the diminished net driving force for Na(+) and allowing salt secretion, even in extreme salinities.

KEYWORDS:

CFTR; Chloride cell; Electrophysiology; Euryhaline; Fundulus heteroclitus; Gill epithelium; Immunocytochemistry; Ionocyte; Teleost fish; Tight junction

PMID:
25750413
DOI:
10.1242/jeb.117317
[Indexed for MEDLINE]
Free full text

Supplemental Content

Full text links

Icon for HighWire
Loading ...
Support Center