Ionic requirement for regulatory cell volume decrease in renal straight proximal tubules

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Abstract
The present study has been performed to test for the ionic requirement of regulatory cell volume decrease in isolated perfused straight proximal tubules of the mouse kidney. Reduction of peritubular osmolarity from 308 mosmol/l to 228 mosmol/l leads within 0.5 min to cell swelling by 16±1% (n=26) of original cell volume (Vo). Within 2 min cell volume (V2) approaches 105±1% ofVo (n=26) despite continued exposure to hypotonic bath perfusate. Reexposure of the tubules to isotonic bath perfusate shrinks the cells to 94±1% ofVo (n=25). Within 2 min from omission of extracellular bicarbonate and CO2 regulatory cell volume decrease is impaired (V2=114±1% ofVo,n=14). Similarly, regulatory volume decrease is blunted upon prior removal of extracellular sodium (Vo=115±2% ofVo,n=12). In constrast regulatory volume decrease is not affected by prior removal of extracellular chloride (V2=104±2% ofVo,n=9). Regulatory volume decrease is impaired in the presence of 1 mmol/l potassium channel blocker barium (V2=120±4% ofVo,n=7) and of 1 mmol/l carbonic anhydrase inhibitor acetazolamide (V2=111±2% ofVo,n=16) but is preserved in the presence of 1 μmol/l chloride channel blocker NPPB, (V2=105±2% ofVo,n=11). In conclusion, regulatory cell volume decrease apparently depends on potassium and bicarbonate, but does not depend on chloride.