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Ammonium transport in collecting ducts
1National Institutes of Health, Bethesda, Md.
Mineral and Electrolyte Metabolism
|January 1, 1990
Summary
Ammonium (NH4+) is secreted into kidney collecting ducts via ammonia (NH3) diffusion, driven by active hydrogen ion (H+) secretion. High NH3 permeability and low NH4+ permeability ensure efficient ammonia transport and prevent backflux.
Area of Science:
- Nephrology
- Renal Physiology
- Urine Concentration Mechanisms
Background:
- Ammonium (NH4+) secretion is crucial for acid-base balance and occurs in kidney collecting ducts.
- Understanding the transport mechanisms of ammonia (NH3) and ammonium (NH4+) is key to comprehending renal function.
Purpose of the Study:
- To elucidate the in vivo and in vitro mechanisms of ammonium secretion in major collecting duct segments.
- To investigate the roles of ammonia (NH3) and ammonium (NH4+) permeability in renal tubular transport.
Main Methods:
- In vivo studies to observe ammonium secretion and concentration gradients.
- In vitro measurements to determine NH3 and NH4+ permeability in collecting duct segments.
Main Results:
- Ammonium is secreted into collecting ducts via passive NH3 diffusion, coupled with active H+ secretion.
- High NH3 permeability (10(-3) to 10(-2) cm/s) and negligible NH4+ permeability were measured.
- Active H+ secretion creates pH disequilibrium, enhancing the NH3 gradient and driving secretion.
Conclusions:
- The collecting duct efficiently secretes ammonium by leveraging passive NH3 diffusion and active H+ transport.
- Low NH4+ permeability prevents backflux, ensuring net ammonia secretion and contributing to acid-base homeostasis.