AI Article Synopsis
- RhAG is crucial for expressing Rh blood group antigens and may also play a role in ammonium transport, as shown by its effect on yeast survival.
- In experiments with HeLa cells expressing GFP-RhAG, researchers found that RhAG enhances the uptake of ammonium (NH4+) and ammonia (NH3), leading to observable changes in intracellular pH (pHi).
- Quantitative analysis revealed that RhAG expression increases NH4+ transport threefold and NH3 transport twofold, providing the first evidence of its role in ammonium transport in human erythroid cells.
Article Abstract
The erythroid Rh-associated glycoprotein (RhAG) is strictly required for the expression of the Rh blood group antigens carried by Rh (D,CE) proteins. A biological function for RhAG in ammonium transport has been suggested by its ability to improve survival of an ammonium-uptake-deficient yeast. We investigated the function of RhAG by studying the entry of NH3/NH4+ in HeLa cells transiently expressing the green fluorescent protein (GFP)-RhAG fusion protein and using a fluorescent proton probe to measure intracellular pH (pHi). Under experimental conditions that reduce the intrinsic Na/H exchanger activity, exposure of control cells to a 10 mM NH4Cl- containing solution induces the classic pHi response profile of cells having a high permeability to NH3 (PNH3) but relatively low permeability to NH4+ (PNH4). In contrast, under the same conditions, the pHi profile of cells expressing RhAG clearly indicated an increased PNH4, as evidenced by secondary reacidification during NH4Cl exposure and a pHi undershoot below the initial resting value upon its removal. Measurements of pHi during methylammonium exposure showed that RhAG expression enhances the influx of both the unprotonated and ionic forms of methylammonium. Using a mathematical model to adjust passive permeabilities for a fit to the pHi profiles, we found that RhAG expression resulted in a threefold increase of PNH4 and a twofold increase of PNH3. Our results are the first evidence that the human erythroid RhAG increases the transport of both NH3 and NH4+.
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| http://dx.doi.org/10.1007/s00424-005-1381-y | DOI Listing |
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