Abstract
1. The fluxes of isotopically labelled sodium, potassium and chloride passing in each direction across isolated sheets of rumen epithelium from the sheep have been measured under short-circuit conditions.2. With both sides of the epithelium bathed in chloride Ringer the mean sodium fluxes were 2.85 mumole/cm(2).hr from rumen to blood and 1.28 mumole/cm(2).hr in the reverse direction. In sulphate Ringer the sodium fluxes were 1.64 mumole/cm(2).hr from rumen to blood and 0.54 mumole/cm(2).hr from blood to rumen.3. In chloride Ringer the mean potassium fluxes were 0.18 mumole/cm(2).hr from rumen to blood and 0.54 mumole/cm(2).hr from blood to rumen. In sulphate Ringer the potassium fluxes were 0.07 mumole/cm(2).hr from rumen to blood and 0.35 mumole/cm(2).hr from blood to rumen.4. In chloride Ringer the mean chloride fluxes were 4.89 mumole/cm(2).hr from rumen to blood and 3.78 mumole/cm(2).hr from blood to rumen.5. In chloride Ringer the mean value of the short-circuit current was 13 muA/cm(2), corresponding to a flux of 0.49 muequiv/cm(2).hr. When sulphate was substituted for chloride, the short-circuit current was increased by about 40%, and the net flux of sodium from rumen to blood fell by 30%.6. Neither the sodium nor the chloride fluxes changed significantly when the epithelium was temporarily open-circuited.