First person – Manh Tin Ho and Jiongming Lu

ABSTRACT First Person is a series of interviews with the first authors of a selection of papers published in Disease Models & Mechanisms, helping early-career researchers promote themselves alongside their papers. Manh Tin Ho and Jiongming Lu are co-first authors on ‘A translation-independent activity of PheRS activates growth and proliferation in Drosophila’, published in DMM. Manh Tin conducted the research described in this article while a PhD student in the lab of Beat Suter at the University of Bern, Bern, Switzerland, and is now a postdoctoral researcher in the lab of Daniel Fuster at the University of Bern, investigating kidney disease and sodium/proton exchange membrane proteins. Jiongming conducted the research described in this article while a PhD student in the lab of Beat Suter at the University of Bern, and is now a postdoctoral researcher in the lab of Linda Partridge at the Max Planck Institute for Biology of Ageing, Köln, Germany, investigating molecular mechanisms and new strategies of healthy ageing.

Modulation of electroneutral Na transport in sheep rumen epithelium by luminal ammonia

Ammonia is an abundant fermentation product in the forestomachs of ruminants and the intestine of other species. Uptake as NH3 or NH4+ should modulate cytosolic pH and sodium-proton exchange via Na+/H+ exchanger (NHE). Transport rates of Na+, NH4+, and NH3 across the isolated rumen epithelium were studied at various luminal ammonia concentrations and pH values using the Ussing chamber method. The patch-clamp technique was used to identify an uptake route for NH4+. The data show that luminal ammonia inhibits electroneutral Na transport at pH 7.4 and abolishes it at 30 mM ( P < 0.05). In contrast, at pH 6.4, ammonia stimulates Na transport ( P < 0.05). Flux data reveal that at pH 6.4, ∼70% of ammonia is absorbed in the form of NH4+, whereas at pH 7.4, uptake of NH3 exceeds that of NH4+ by a factor of approximately four. The patch-clamp data show a quinidine-sensitive permeability for NH4+ and K+ but not Na+. Conductance was 135 ± 12 pS in symmetrical NH4Cl solution (130 mM). Permeability was modulated by the concentration of permeant ions, with PK > PNH4 at high and PNH4 > PK at lower external concentrations. Joint application of both ions led to anomalous mole fraction effects. In conclusion, the luminal pH determines the predominant form of ammonia absorption from the rumen and the effect of ammonia on electroneutral Na transport. Protons that enter the cytosol through potassium channels in the form of NH4+ stimulate and nonionic diffusion of NH3 blocks NHE, thus contributing to sodium transport and regulation of pH.