Effect of D-glucose and L-glutamate on the kinetics of bicarbonate reabsorption in rat proximal tubules.

The effect of D-glucose or L-glutamate on the kinetics of bicarbonate reabsorption in the early (EPT) and middle proximal tubule (MPT) was studied in vivo in Munich-Wistar rats by microperfusion techniques. The presence of 20 mM D-glucose in the lumen increased acidification half-time (t/2) (from 2.54 +/- 0.09 s to 3.11 +/- 0.17 s in EPT and from 4.75 +/- 0.20 s to 6.04 +/- 0.49 s in MPT). Bicarbonate reabsorption (JHCO3-) decreased as a consequence of this change (from 3.80 +/- 0.17 to 2.46 +/- 0.20 nmol cm-2 s-1 in EPT and from 2.30 +/- 0.10 to 1.64 +/- 0.10 nmol cm-2 s-1 in MPT). In this situation the basolateral membrane potential difference (BLMPD) in the MPT decreased from -41.6 +/- 2.47 to -29.7 +/- 2.45 mV and returned to control values after perfusion with D-glucose. The addition of 20 mM L-glutamate to the luminal perfusion caused an opposite effect, i.e., a decrease in t/2 (1.54 +/- 0.21 s in EPT and 3.25 +/- 0.26 s in MPT) and a consequent increase in JHCO3- in both segments (5.09 +/- 0.58 nmol cm-2 s-1 in EPT and 3.92 +/- 0.30 nmol cm-2 s-1 in MPT). The BLMPD of MPT increased during L-glutamate perfusion (-39.0 +/- 2.48 mV in control and -52.0 +/- 2.72 mV with L-glutamate) and returned to control values after perfusion.(ABSTRACT TRUNCATED AT 250 WORDS)