Studies on the Capacity (Tm) of Renal Tubular Na+ -Transport and of Some Rate Determining Pharmacological Factors / Untersuchungen zur Frage eines renalen Tmax von Na+ und seiner pharmakologischen Beeinflußbarkeit
From results of in vivo studies on mammalian kidneys it is inferred that a linear relationship exists between the filtered Na+ -load and the amount of tubular net-Na+ -reabsorption. Under in vivo conditions it is impossible to increase Na+ -plasma concentration to more than 220 mMol/l. Therefore the experimental possibilities to vary the filtered load are limited. The isolated kidney has in contrary the adventage that the filtered load can be varied over a wide range. To analyse, whether a limited reabsorption rate of sodium does exist or not isolated kidneys of Rana ridibunda were perfused with solutions containing 5.0–191.5 mMol/1 sodium. In order to study the influence of the anion on Na+ -net-reabsorption Na+ -cyclohexansulphamate- (NaCHS, a slowly penetrating anion), and mixtures of NaCl, and Na+ -hydrogencarbonate- (a swiftly penetrating anion) of varying concentrations were used. Furthermore, the influence of lack of K+ (perfusion with K+ -free media) and of Furosemide on the TmNa+ was tested.