title: Electrophysiology of ammonia transport in renal straight proximal tubules.
abstract: To test for electrogenic transport of ammonium ions in straight proximal renal tubules, isolated perfused tubules have been exposed to peritubular ammonium ions during continuous recording of cell membrane potential. As a result, 20 mmol/liter NH4+ leads to a rapid, reversible depolarization of the cell membrane by 9.0 +/- 0.3 mV (N = 86). This depolarization is not significantly affected by 10 mmol/liter barium or 0.1 mmol/liter amiloride on both sides of the epithelium, but is significantly blunted by omission of extracellular bicarbonate and CO2 (3.8 +/- 0.4 mV, N = 9), by 1 mmol/liter acetazolamide (4.3 +/- 0.3 mV, N = 11), by 1 mmol/liter peritubular amiloride (4.3 +/- 1.1 mV, N = 7), by 1 mmol/liter SITS (5.7 +/- 0.4 mV, N = 6), and by replacement of extracellular sodium with choline (4.7 +/- 0.5 mV, N = 8). In the presence of both amiloride (1 mmol/liter) and acetazolamide (1 mmol/liter) in the bath, the NH4+ induced depolarization is completely abolished. Furthermore, the combined omission of bicarbonate and addition of 10 mmol/liter barium eliminates the NH4+ induced depolarization. About 50% of the depolarization can be explained by enhanced electrogenic bicarbonate exit due to the intracellular alkalosis. The other 50% is explained by amiloride and barium sensitive electrogenic entry of NH4+ into the cell.
authors.affiliation: Institute for Physiology, University Innsbruck, Austria.
authors.forename: H
authors.initials: H
authors.lastname: Völkl
authors.forename: F
authors.initials: F
authors.lastname: Lang
mesh_terms: D000086:Acetazolamide / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D000641:Ammonia / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000494:pharmacology; D001639:Bicarbonates / Q000494:pharmacology; D001693:Biological Transport, Active / Q000187:drug effects; D004594:Electrophysiology; D066298:In Vitro Techniques; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D010477:Perfusion
chemical_list: D001639:Bicarbonates; D001464:Barium; D000641:Ammonia; D000584:Amiloride; D000086:Acetazolamide