Effect of P-Chloromercuribenzoate (pCMB), Ouabain and 4-Acetamido-4′ISO-Thiocyamatostilbene-2,2′-Disulfonic Acid (Sits) on Proximal Tubular Transport Processes

Abstract

Using microperfusion techniques the following transport parameters of the proximal tubule were measured: 1. Isotonic fluid (Na⁺) absorption (J_Na). 2. Zero net flux concentration (electrochemical potential) differences which are proportional to the respective active transport rates of H⁺ Cglycodiazine), D-glucose (α-methyl-D-glycoside), L-histidine, inorganic phosphate and calcium ions. 3. Transtubular and transcellular electrical potential differences and transcellular resistances.

The following was found:

• 1. Ouabain (1mM) applied peritubularly in golden hamsters inhibited J_Na incompletely and the sodium-coupled (secondary active) transport processes of glucose, histidine, phosphate and Ca⁺⁺ by more than 80%. The H⁺ (glycodiazine) transport was not affected. Ouabain (1mM) plus acetazolamide (0.2 mM) inhibited J_Na completely.

• 2. In the rat, pCMB (0.2 mM) when applied long enough, inhibits J_Na completely. At a time of pCMB application when J_Na is reduced to 1/3, this substance inhibits the active H⁺ (glycodiazine) transport which must be considered to be a direct action of pCMB. Furthermore it inhibits the secondary active phosphate transport either directly or via the inhibition of Na⁺ and/or H⁺ transport. The secondary active glucose, histidine and Ca⁺⁺ transport are little affected by pCMB. pCMB reduces the cell potential, reversibly, yet leaves unchanged the resistance ratio of the luminal to peritubular cell membrane .

• 3. In the rat SITS inhibits J_Na moderately but the active H⁺ (glycodiazine) transport strongly. It does not affect the glucose transport.

On the basis of these and other results a hypothesis of the interaction of Na⁺ and H⁺ (HCO₃ ^-) transport is given.