Effect of potassium on cell volume regulation in renal straight proximal tubules

The present study was designed to assess for the influence of extracellular potassium and of inhibitors of potassium transport on cell volume regulatory decrease in isolated perfused straight proximal tubules of the mouse kidney. Volume regulatory decrease is virtually unaffected when bath potassium concentration is elevated from 5 to 20 mmol/liter, and still persists, albeit significantly retarded, in the presence of the potassium channel blocker barium on both sides of the epithelium and during virtually complete dissipation of the transmembrane potassium gradient by increasing extracellular potassium concentration to 40 mmol/liter. As evident from electrophysiologic observations, barium blocks the potassium conductance of the basolateral cell membrane. Reduction of bicarbonate concentration and increase of H+ concentration in the bath solution cannot compensate for enhanced potassium concentration and cell volume regulatory decrease is not affected in the presence of the K/H exchange inhibitor omeprazole. Similarly cell volume regulatory decrease is not affected by ouabain. In conclusion, potassium movements through potassium channels in the basolateral cell membrane are important determinants of cell volume and may participate in cell volume regulatory decrease. However, a powerful component of cell volume regulatory decrease in straight proximal tubules of the mouse kidney is apparently independent of potassium conductive pathways, K/H exchange and Na+/K(+)-ATPase.