AJP - Renal Physiology, Vol 249, Issue 5 704-F712, Copyright © 1985 by American Physiological Society
Segmental localization of the rabbit renal proximal tubular Na+-H+ exchange system
U. Kragh-Hansen, H. Roigaard-Petersen and M. I. Sheikh
The activity of the Na+-H+ exchanger in rabbit proximal tubule was
investigated by using luminal membrane vesicles prepared from "outer
cortex" (proximal convoluted tubule) or "outer medulla" (proximal straight
tubule). The purity of the preparations was examined by measuring the
activity of several marker enzymes, and the degree of cross-contamination
and the functional state of the membrane vesicles were assessed by studying
Na+-dependent uptake of D-glucose. The Na+ uptake by pars convoluta
membrane vesicles exhibited an overshoot in the presence of an
intravesicular greater than extravesicular H+ gradient. The overshoot was
eliminated by omitting or reversing the transmembranal H+ gradient or by
adding amiloride. In contrast, Na+ uptake by pars recta membrane vesicles
did not show an overshoot and was independent of H+ gradients and of
amiloride. However, Na+ uptake by pars recta membrane vesicles pretreated
with monensin exhibited an overshoot. This overshoot apparently was
amiloride insensitive. The findings propose that the Na+-H+ exchanger is
predominantly operative in the proximal convoluted tubule and is either
lacking or of minor significance in the proximal straight tubule.
