Collecting duct‐specific Rh C Glycoprotein deletion alters basal and acidosis‐stimulated renal ammonia metabolism

Abstract

Renal collecting duct NH3 secretion is a key element of acid‐base regulation and has been attributed to passive diffusion. Mammalian Rh Glycoproteins are similar to Mep/Amt ammonia transporters in other organisms.[jvr1] Rh C Glycoprotein (Rhcg) is expressed in the collecting duct. To determine if the collecting duct secretes NH3 via Rhcg, we generated mice with collecting duct‐specific Rhcg deletion (KO), which we confirmed by immunohistochemistry. KO mice had loxP sites in introns 4 and 9 of the Rhcg gene (Rhcgfl/fl) and expressed Cre‐recombinase under control of the Ksp‐cadherin promoter (Ksp‐Cre). Control (C) mice were Rhcgfl/fl but Ksp‐Cre‐negative. Basal urinary ammonia excretion was less in KO vs C mice (71±9 vs 94±6 μmol d−1, n=8 and 6, p<0.05). In mice acid‐loaded by adding 0.4M HCl to normal rodent chow, day 1 urinary ammonia excretion did not change significantly in KO mice (Δ=‐16±19 μmol d−1, n=6, p=NS), whereas it increased significantly in C mice (Δ=154±37 μmol d−1, n=6, p<0.005). Urinary ammonia excretion was significantly less in KO vs C mice each subsequent day. After 7 days, metabolic acidosis, measured as serum [HCO3−], was more severe in KO than C mice (16.2±1.0 vs 20.5±0.8 mmol/L, p<0.02, n=6 and 5). Other differences between acid‐loaded KO and C mice included lower urine pH at day 2 and decreased glutamine synthetase and increased PEPCK and Rhbg expression at day 7 in KO mice. We conclude: 1) collecting duct ammonia secretion is, at least in part, mediated by Rhcg and not due solely to passive NH3 diffusion; and 2) during metabolic acidosis compensatory responses to Rhcg deletion contribute to partial increases in ammonia excretion.This work was supported by NIDDK.