Reabsorption of HCO3 Apical membranes of tubule cells are impermeable to HCO3 Reabsorption is indirect when urine is acidic, hco combines with h+ to form H,CO3, which is catalyzed by ca located in the apical cell membrane of PCT ximal convoluted tubule )I As [CO2]increases in the filtrate Co2 diffuses into tubule cell and forms H2 CO3 H Co dissociates to Hco and H+ HCO3 generated within tubule cell diffuses into peritubular capillary.Reabsorption of HCO3 - ◼ Apical membranes of tubule cells are impermeable to HCO3 - . ◼ Reabsorption is indirect. ◼ When urine is acidic, HCO3 - combines with H+ to form H2CO3 - , which is catalyzed by ca located in the apical cell membrane of PCT (proximal convoluted tubule) . ◼ As [CO2] increases in the filtrate, CO2 diffuses into tubule cell and forms H2CO3 . ◼ H2CO3 dissociates to HCO3 - and H+ . ◼ HCO3 - generated within tubule cell diffuses into peritubular capillary