No abstract

K. J. DEGNAN AND OTHERS net Cl-blood side to seawater side flux of 162-8 isA/cm2 which was not statistically different (P > 0.70) from the mean short-circuit current of 158-6 + 163 ,uA/cm2 for these flux studies. The mean Na+ blood side to seawater side flux was 32-2 + 3-3 ,uA/cm2 and the mean Na+ seawater side to blood side flux was 34-8 + 4-1 isA/cm2, 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 % 02/5 % CO2.5. Ouabain (105 M), furosemide (10-3 M), thiocyanate (10-2 M), adrenaline (1I0 M), and anoxia (100 % N2) decreased the short-circuit current 92*7, 85-0, 45-3, 62-6, and 83'3 % respectively. Theophylline (104 M) stimulated the short-circuit current 54-9 %. Increasing the HC03-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. heteroclitU8, when bathed on both sides with Ringer, displayed a mean short-circuit current of 94-1 + 10 4 #sA/cm2, 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 Q. cm2 (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 ,uA/cm2 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 IzA/cm2, 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 Q.cm2 (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 ,uA/cm2 and a net Na+ blood side to seawater side flux of 65'3 + 28-6 ,uA/cm2.

The opercular epithelium of Fundulus heteroclitus contains typical gill chloride-secreting cells at the high density of 4 X 10(5) cells per square centimeter. When isolated, mounted as a membrane, and short-circuited, it actively transports chloride ions from the blood side to the seawater side of the preparation. This preparation offers a useful approach to the study of osmoregulation in bony fishes.