Bicarbonate reabsorption and potassium handling in isolated perfused kidneys of Bufo marinus

Abstract

Average rates of bicarbonate reabsorption, normalized for glomerular filtration rates, rose linearly with perfusate [HCO3-] of 6-21 mM with a constant bicarbonate/creatinine clearance ratio of 0.06, similar to the in vivo value. Maximal rates of bicarbonate reabsorption occurred at 20-25 mM HCO3- perfusate. At 3 mM perfusate [K+], normalized rates of potassium reabsorption were constant from filtered perfusates mimicking metabolic acidosis, and from control perfusates; during perfusion with alkalotic Ringer solutions net potassium secretion was observed. Elevation of perfusate [K+] to 10 mM in alkalotic Ringer significantly decreased maximal rates of bicarbonate reabsorption. Overall, the pattern of bicarbonate reabsorption in toad kidneys perfused at 6-21 mM HCO3- was similar to that observed in acid-base disturbances of metabolic origin in mammals, while the pattern of potassium excretion showed significant differences in these two vertebrate classes.