ASSESSMENT OF THE PROXIMAL TUBULAR FUNCTION IN THE OBSTRUCTED KIDNEY USING MICROPUNCTURE TECHNIQUE

Abstract

The mechanism and the capacity of proximal tubular reabsorption during complete unilateral ureteral obstruction (CUUO) were assessed in rats using micropuncture techniques. Peritubular membrane potential (E_Mperi), intracellular potassium activity (aⁱ_K) and transtubular potential (E_MTT) were determined using K⁺-sensitive double barreled microelectrode. In control, E_Mperi and aⁱ_K were -68.7mV and 81.2mEq/l, respectively. In 1 day' CUUO, E_Mperi and aⁱ_K were -58.1mV and 68.8mEq/l, respectively. Further progressive decrease in E_Mperi and aⁱ_K were noticed with the duration of CUUO. However, all aⁱ_K observed in CUUO was still above electrochemical equilibrium. These data suggest that Na-K pump activity is partially preserved in CUUO. Consequently, active Na⁺ transport followed by fluid reabsorption must exist in CUUO. Thus, reabsorptive mechanisms of control and CUUO were considered to be essentially the same. The effect of obstruction on E_MTT was marginal. Using Split Oil Drop method, the amount of fluid reabsorption (J_VL) along proximal tubule was determined in control and 3 days's CUUO. Two different test solutions were Ringer' solution and Na⁺-free (Choline Cl) solution. In 3 days' CUUO, mean J_VL was 0.0065nl/sec nm (22% of control) and the magnitude of J_VL was proportional to the E_Mperi value. With Na⁺-free solution J_VL was almost zero in both control and 3 days' CUUO. In conclusion, proximal tubular reabsorption plays an important role in maintaining glomerular filtration relatively intact during CUUO.