Ion transport across an isolated preparation of sheep rumen epithelium.

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.