[Microperfusion and electrophysiologic study of the proximal tubules of Triturus vulgaris and rat kidneys].

Studies have been made on changes in Na and K concentrations in the lumen of the proximal tubule of the kidney of rat and newt during perfusion of the tubuli by solutions containing various concentrations of these ions. Intraluminar concentration of Na and K is rapidly changed and towards the end of the perfused region the ratio of Na and K concentration in the lumen to the concentration in the blood plasma approaches 1. Within the lumen of the perfused proximal tubuli of newt's kidney, Na and K concentrations are changed insignificantly as compared to the concentration of these ions in perfusion solutions. Proximal tubuli of the newt and rat exhibit low transepithelial potential, i. e. -0.27 +/- 0.15 and -3.59 +/- 0.16 mV correspondingly. The specific resistance of the wall of the proximal tubuli in the newt is 10 times higher than in rat. From changes in transepithelial diffusion potential, the following sequence of coefficients of ionic permeability for the proximal tubuli of the newt was calculated: PNa+:PK+:PCh+:PCl-:PNO3-=1 : 1.15: 0.96 : 2.86 : 3.21. The data obtained indicate that in rats as compared to the newt, proximal tubuli exhibit higher transepithelial conductivity, higher passive permeability for ions and different selectivity for anions and cations.