Intracellular potential and K+ activity in rat kidney proximal tubular cells in acidosis and K+ depletion

Abstract

Techniques were developed for the measurement of intracellular potentials and potassium activities in rat proximal tubule cells using double barreled K⁺ liquid-ion-exchanger microelectrodes. After obtaining measurements of stable and reliable control values, the effects of K⁺ depletion and metabolic and respiratory acidosis on the intracellular potential and K⁺ activity in rat kidney proximal tubular cells were determined. At a peritubular membrane potential of −66.3±1.3 mV (mean±se), intracellular K⁺ activity was 65.9±2.0 mEq/liter in the control rats. In metabolic acidosis [70 mg NH₄ Cl/100 g body wt) the peritubular membrane potential was significantly reduced to −47.5±1.9 mV, and cellular K⁺ activity to 53.5±2.0 mEq/liter. In contrast, in respiratory acidosis (15% CO₂) the peritubular membrane potential was significantly lowered to −46.1±1.39 mV, but the cellular K⁺ activity was maintained at an almost unchanged level of 63.7±1.9 mEq/liter. In K⁺ depleted animals (6 weeks on low K⁺ diet), the peritubular membrane potential was significantly higher than in control animals, −74.8±2.1 mV, and cellular K⁺ activity was moderately but significantly reduced to 58.1±2.7 mEq/liter. Under all conditions studied, cellular K⁺ was above electrochemical equilibrium. Consequently, an active mechanism for cellular K⁺ accumulation must exist at one or both cell membranes. Furthermore, peritubular HCO₃ ⁻ appears to be an important factor in maintaining normal K⁺ distribution across the basolateral cell membrane.