Electrophysiology of cell volume regulation in proximal tubules of the mouse kidney

Abstract

The present study has been designed to test for the influence of cell swelling on the potential difference and conductive properties of the basolateral cell membrane in isolated perfused proximal tubules. During control conditions the potential difference across the basolateral cell membrane (PD_bl) is −65±1 mV (n=74). Decrease of peritubular osmolarity by 80 mosmol/l depolarizes the basolateral cell membrane by +7.8±0.5 mV (n=42). An increase of bath potassium concentration from 5 to 20 mmol/l depolarizes the basolateral cell membrane by +25±1 mV (n=11), an increase of bath bicarbonate concentration from 20 to 60 mmol/l hyperpolarizes the basolateral cell membrane by −3.2±0.5 mV (n=13). A decrease of bath chloride concentration from 79.6 to 27 mmol/l hyperpolarizes the basolateral cell membrane by −1.8±0.7 mV (n=6). During reduced bath osmolarity, the influence of altered bath potassium concentration on PD_bl is decreased (Δ PD_bl=+16±2 mV,n=11), the influence of altered bicarbonate concentration on PDbl is increased (Δ PD_bl=−6.0±0.8 mV,n=13), and the influence of altered bath chloride concentration on PD_bl is unaffected (Δ PD_bl=−1.8±0.6 mV,n=6). Barium depolarizes the basolateral cell membrane to −28±2 mV (n=16). In the presence of 1 mmol/l barium, decrease of peritubular osmolarity by 80 mosmol/l leads to a transient hyperpolarization of the basolateral cell membrane by −5.9±0.5 mV (n=16). This transient hyperpolarization is blunted in the absence of extracellular bicarbonate. In conclusion, cell swelling depolarizes straight proximal tubule cells and increases bicarbonate selectivity of the basolateral cell membrane at the expense of potassium selectivity. The data reflect either incrases of bicarbonate conductance or decrease of potassium conductance during exposure of proximal tubule cells to hypotonic media.