Transepithelial HCO2- handling

Question 1

Proximal tubule Hc03- reabsorption - overall process? WHat happens once in cell?

Answer 1

Co2 produced in lumen of proximal tubule and taken up across apical membrane
Recombines in cell with H20 in presence of carbonic anhydrase to produce H+ + HCO3- –> exits cell at basolateral membrane via the Na+/HCo3- cotransporter

Question 2

Stoichiometry of Na+/Hco3- co transporter?

Answer 2

1 Na+ for every 3 Hco3- –> this is needed for proper HCo3- reabsorption

Question 3

What stimulates Hco3- reabsorption? What is this linked to

Answer 3

Angiotensin ||, endothelin |, noradrenaline and adenosine

linked to increases in Ca2+ and PKC

Question 4

What downregulates Hco3- reabsorp? What is this linked to

Answer 4

ANP, dopamine, parathormone. This is linked to cAMP/PKA pathway

Question 5

WHat is acting as the indicator therefore for hco3- absorption?

Answer 5

Blood co2 levels - proximal tubule senses blood co2 levels and alters transport accordingly