Peculiarities of the Na+/D-glucose cotransport system in Necturus renal tubules.

The effects of D-glucose addition to a glucose-free luminal perfusate were investigated in the proximal tubule of Necturus kidney, by electrophysiological techniques. The main findings are: (1) In the presence of sodium, D-glucose produces 10.5 mV +/- 1.1 (S.E.) depolarization. (2) Phlorizin reduces the magnitude of this response to 2.1 +/- 0.1 mV. (3) The glucose-evoked depolarization, delta VG, does not alter the intracellular K+ activity nor is it affected by peritubular addition of ouabain. (4) Isosmotic reduction of Na+ concentration in luminal perfusate from 95 to 2 mmol/l (choline or Li+ substituting for Na+) does not change the magnitude of delta VG; complete removal of sodium from the lumen lowers the value of delta VG (3.2 +/- 0.2 mV) but the response is not abolished. This observation suggests that the D-glucose carrier of renal tubules in Necturus is poorly specific with regard to the cotransported cation species.