Location
- Predominantly occurs in the distal convoluted tubules
Process
- Glutamine is converted by tubular cells to form ammonia ( NH3) and glutamic acid
- Ammonia diffuses into the tubular lumen and combines with H+ to form ammonium ions (NH4+)
- Can accompany negatively charged anions, such as the strong ion chloride, conserving Na+ and K+
- Process is increased in acidosis:
- Increased activity of glutaminase, the enzyme catalysing the conversion of glutamine
- Preference by the liver to convert NH4+ ions and HCO3- into glutamate rather than urea
- Increase activity takes 3-4 days to reach maximum capacity in the setting of acidosis
Result
- Trapping of H+ ions in urine to allow excretion
- Excreted of one H+ ion per molecule of glutamine metabolised
- Generation of a cation to allow excretion of Cl- without K+ or Na+