Hypertonicity Decreases Basolateral K+ and Cl− Conductances in Rabbit Proximal Convoluted Tubule

Abstract.: Collapsed proximal convoluted tubules (PCT) shrink to reach a volume 20% lower than control and do not exhibit regulatory volume increase when submitted to abrupt 150 mOsm/kg hypertonic shock. The shrinking is accompanied by a rapid depolarization of the basolateral membrane potential (V _BL) of 8.4 ± 0.5 mV, with respect to a control value of −54.5 ± 1.9 mV (n= 15). After a small and transient hyperpolarization, V _BL further depolarizes to reach a steady depolarization of 19.5 ± 1.5 mV (n= 15) with respect to control. In the post-control period, V _BL returns to −55.8 ± 1.5 mV. The basolateral partial conductance to K⁺ (t _K ) which is 0.17 ± 0.01 (n= 5) in control condition, decreases rapidly to nonmeasurable values during the hypertonic shock and returns to 0.23 ± 0.03 in the post-control period. The basolateral partial conductance to Cl⁻ (t _Cl), which is 0.05 ± 0.02 (n= 5) in control, also decreases in hypertonicity to a nonmeasurable value and returns to 0.03 ± 0.01 in post control. The partial conductance mediated by the Na-HCO₃ cotransporter (t _NaHCO3), which is 0.48 ± 0.06 (n= 5) in control condition, remains the same at 0.44 ± 0.05 (n= 5) during the hypertonic period. Similarly, the membrane absolute conductance mediated by the Na-HCO₃ cotransporter (G _Na-HCO3) does not vary appreciably. Concomitant with cell shrinkage, intracellular pH (pH _i ) decreases from a control value of 7.26 ± 0.01 to 7.13 ± 0.02 (n= 12) and then remains constant. Return to control solution brings back pH _i to 7.28 ± 0.03. From these results, we conclude that in collapsed PCT, a sustained decrease in cellular volume leads to cell acidification and to inhibition of K⁺ and Cl⁻ conductances.