Active sodium transport across the epithelium of the human kidney pelvis. Part 1.

To clarify whether the epithelium of the human urinary tract possesses an active transepithelial sodium transport, the unidirectional sodium fluxes and the electrical parameters of the epithelium were determined on isolated pieces of renal pelvis. The epithelium was incubated in isotonic Ringer's solution at 37.3C in Ussing-type chambers. The transepithelial potential difference was found to be 15.8 +/- 3.0 mV and the transepithelial electrical resistance 760 +/- 48 omega . cm.-2. The transepithelial, unidirectional sodium fluxes were measured under short-circuit conditions. From both the unidirectional sodium influx from the luminal to the serosal side (7.01 +/- 2.17) and from the efflux in the opposite direction (0.45 +/- 0.07) a transepithelial sodium net flux of 6.56 +/- 2.20 nmol. . minutes-1. cm.-2 was calculated. Since there are no passive forces across the epithelium under short circuited conditions to explain the net flux, an active sodium transport has to be postulated. In all experiments, the simultaneously measured short circuit current (6.43 +/- 2.18 nmol. . minutes-1 . cm-2) was not significantly different from the net sodium flux, and can therefore be taken as a measure of the net flux.