The effect of pH on sugar transport and ion distribution in kidney cortex cells

Abstract

The effect of pH (range: 6.2–8.2) on active sugar transport and the steady-state ionic distribution was studied using slices of rabbit kidney cortex. Sugars used: 2-deoxy- d-glucose, 2-deoxy- d-galactose, d-galactose and α-methyl- d-glucoside. 1. 1. An increase of pH from 6.2 to 8.2 affected sugar transport as follows: (a) A 3-fold increase in the rate and steady-state accumulation of 2-deoxy- d-glucose both in Na +- and Na +-free (Li +) salines was found; changes of pH affected the K m of 2-deoxy- d-glucose transport. (b) A marked decrease of the accumulation of 2-deoxy- d-galactose in both Na +- and Li +-salines was observed, the transport K m being affected. (c) A 4-fold stimulation of d-galactose transport in Na 2+-saline took place, with only a minimial effect on the Na +-independent transport. This pH effect was reversible. An increase of pH from 7.2 to 8.2 markedly decreased the efflux of d-galactose from the cells. Evidence for complex influx kinetics was obtained. (d) No major changes of the steady-state accumulation of α-methyl- d-glucoside in Na +-salines could be detected; in Li +-saline, an accumulation of α-methyl- d-glucoside at pH 6.2 was found ( [S] 1/[S] 0: 1.725 ± 0.101 ( S.E.) . This active accumulation at [ Na +] 0 = 0 (and [ Na +] i < 3 mM ) was inhibited to [S] 1/[S] 0 values below 1.0 by anaerobiosis, and by 0.1 mM dinitrophenol or phlorrhizin, but was insensitive to 0.5 mM ouabain or acetazolamide. 2. 2. The increase of pH from 6.2 to 8.2 affected as follows the steady-state tissue water and the respective electrochemical ionic potential (referred to E 36 Cl − ): (a) In Na +-salines, tissue water, E 36 Cl − and E K + were minimally altered; E Na + and E H + decreased. (b) In Li +-salines, tissue water markedly increased with increasing pH; E 36 Cl − was of the same order as in Na +-salines; E K + , lower at pH 6.2 than in Na +-saline, significantly decreased; a small electrochemical gradient of Li + at pH 6.2 (12 mV) decreased; E H + was of the same magnitude as in Na +-salines at all pH. 3. 3. The active transport of α-methyl- d-glucoside at pH 6.2 in the absence of Na + was found to be independent of all ionic electrochemical gradients with the exception of Li +. It is concluded that the four sugars tested are transported into kidney cortex cells by a variety of pathways which do not appear to be related to the demonstrated active, independent mechanisms for H + and K + transport. A Li + dependency for the active transport of α-methyl- d-glucoside in the absence of Na + was observed.