In respiratory acidosis and renal tubular cells
Renal tubular cells have carbonic anhydrase this can produce HCO3- and H+ from CO2. In presence increased CO2 secondary to respiratory acidosis more bicarbonate and Hydrogen ions are produced. These cells secrete Hydrogen ion into the tubular fluid in exchange for sodium. Bicarbonate is actively reabsorbed into peritubular capillary. For each hydrogen ion secreted into tubular fluid one sodium and one bicarbonate ion is absorbed.
In Respiratory alkalosis kidney decreases H+ secretion and depresses HCO3− reabsorption