Active chloride transport in the in vitro opercular skin of a teleost (Fundulus heteroclitus), a gill-like epithelium rich in chloride cells

Abstract

1. The opercular epithelium lining the inside of the gill chamber of the killifish, Fundulus heteroclitus, contains Cl(-) cells, identical in fine structure to gill Cl(-) cells, at the high density of 4 x 10(5) cells/cm(2). This epithelium can be isolated, mounted in a Lucite chamber, and its ion transport properties studied with the short-circuit current technique.2. The isolated opercular epithelia of seawater-adapted fish, when bathed on both sides with Ringer and gassed with 100% O(2), displayed a mean short-circuit current of 136.5 +/- 11.1 muA/cm(2), a mean transepithelial potential difference of 18.7 +/- 1.2 mV (blood side positive), and a mean transepithelial d.c. resistance of 173.7 +/- 12.1 Omega.cm(2) (mean +/- S.E. of mean; n = 64).3. The transepithelial potential difference across the opercular epithelia of seawater-adapted fish was dependent on both Na(+) and Cl(-) in the bathing solutions and increased linearly with increasing Cl(-) concentrations with a slope of 28.3 +/- 2.1 mV/tenfold concentration change. The short-circuit current was Na(+) dependent and increased linearly with increasing Cl(-) concentrations with no evidence of saturation kinetics below 142.5 m-equiv/l.4. When the short-circuited epithelia of seawater-adapted fish, bathed on both sides with Ringer, was gassed with 100% O(2) the mean Cl(-) blood side to seawater side flux was 211.7 +/- 27.1 muA/cm(2) and the mean Cl(-) seawater side to blood side flux was 48.9 +/- 10.0 muA/cm(2). This resulted in a net Cl(-) blood side to seawater side flux of 162.8 muA/cm(2) which was not statistically different (P > 0.70) from the mean short-circuit current of 158.6 +/- 16.3 muA/cm(2) for these flux studies. The mean Na(+) blood side to seawater side flux was 32.2 +/- 3.3 muA/cm(2) and the mean Na(+) seawater side to blood side flux was 34.8 +/- 4.1 muA/cm(2), resulting in no significant (P > 0.20) net flux of this cation. Similar results were obtained with short-circuited epithelia of seawater-adapted fish when bathed on both sides with Ringer and gassed with 95% O(2)/5% CO(2).5. Ouabain (10(-5)M), furosemide (10(-3)M), thiocyanate (10(-2)M), adrenaline (10(-6)M), and anoxia (100% N(2)) decreased the short-circuit current 92.7, 85.0, 45.3, 62.6, and 83.3% respectively. Theophylline (10(-4)M) stimulated the short-circuit current 54.9%. Increasing the HCO(3) (-) concentration in the bathing solutions had a stimulatory effect on the short-circuit current and the potential difference across epithelia from seawater-adapted fish.6. The opercular epithelia of freshwater-adapted F. heteroclitus, when bathed on both sides with Ringer, displayed a mean short-circuit current of 94.1 +/- 10.4 muA/cm(2), a mean transepithelial potential difference of 14.8 +/- 1.9 mV (blood side positive), and a mean d.c. resistance of 169.0 +/- 14.0 Omega.cm(2) (mean +/- S.E. of mean; n = 20). Isotope flux studies across these short-circuited epithelia revealed a net Cl(-) blood side to freshwater side flux of 95.2 +/- 16.1 muA/cm(2) and no significant net flux of Na(+).7. The opercular epithelia of 200% seawater-adapted F. heteroclitus, when bathed on both sides with Ringer, displayed a mean short-circuit current of 33.5 +/- 8.5 muA/cm(2), a mean transepithelial potential difference of 10.5 +/- 2.5 mV (blood side positive), and a mean transepithelial d.c. resistance of 440.7 +/- 62.6 Omega.cm(2) (mean +/- S.E. of mean n = 18). Isotope flux studies across these short-circuited epithelia revealed a net Cl(-) blood side to seawater side flux of 96.2 +/- 51.5 muA/cm(2) and a net Na(+) blood side to seawater side flux of 65.3 +/- 28.6 muA/cm(2).