Abstract. The hypothesis that increased dietary protein augments distal nephron acidification and does so through an endothelin (ET-1)-dependent mechanism was tested. Munich-Wistar rats that ate minimum electrolyte diets of 50% (HiPro) and 20% (CON) casein-provided protein, the latter comparable to standard diet, were compared. HiPro versus CON had higher distal nephron net HCO 3 reabsorption by in vivo microperfusion (37.8 Ϯ 3.2 versus 16.6 Ϯ 1.5 pmol/mm per min; P Ͻ 0.001) as a result of higher H ϩ secretion (41.3 Ϯ 4.0 versus 23.0 Ϯ 2.1 pmol/mm per min; P Ͻ 0.002) and lower HCO 3 secretion (Ϫ3.5 Ϯ 0.4 versus Ϫ6.4 Ϯ 0.8 pmol/mm per min; P Ͻ 0.001). Perfusion with H ϩ inhibitors support that increased H ϩ secretion was mediated by augmented Na ϩ /H ϩ exchange and H ϩ -ATPase activity without augmented H ϩ ,K ϩ -ATPase activity. HiPro versus CON had higher levels of urine ET-1 excretion, renal cortical ET-1 addition to microdialysate in vivo, and renal cortical ET-1 mRNA, consistent with increased renal ET-1 production. Oral bosentan, an ET A/B receptor antagonist, decreased distal nephron net HCO 3 reabsorption (22.4 Ϯ 1.9 versus 37.8 Ϯ 3.2 pmol/mm per min; P Ͻ 0.001) as a result of lower H ϩ secretion (28.4 Ϯ 2.4 versus 41.3 Ϯ 4.0 pmol/mm per min; P Ͻ 0.016) and higher HCO 3 secretion (Ϫ6.0 Ϯ 0.7 versus Ϫ3.5 Ϯ 0.4 pmol/mm per min; P Ͻ 0.006). The H ϩ inhibitors had no additional effect in HiPro ingesting bosentan, supporting that ET mediated the increased distal nephron Na ϩ /H ϩ exchange and H ϩ -ATPase activity in HiPro. Increased dietary protein augments distal nephron acidification that is mediated through an ET-sensitive increase in Na ϩ /H ϩ exchange and H ϩ -ATPase activity.The routine acid challenges to systemic acid-base status faced by humans are modest compared with the large acid loads administered to animals in most experimental protocols. Augmented distal rather than proximal nephron acidification is the predominant renal regulatory response in experimental animals to modest dietary acid loads induced by acid-producing mineral salts (1,2). Augmented distal nephron acidification induced by dietary acid is mediated by multiple mechanisms, including (1) increased net HCO 3 reabsorption (3), consistent with increased H ϩ secretion; (2) reduced HCO 3 delivery to the terminal distal nephron (4) that facilitates NH 4 ϩ secretion (5) and permits secreted H ϩ to effect acid excretion rather than HCO 3 reclamation; and (3) decreased distal nephron HCO 3 secretion (1) mediated by endogenous endothelins (ET) (2).In contrast with the acid-producing mineral salts that are most commonly used to induce an acid challenge in experimental protocols, increased intake of dietary protein that contains acid-producing amino acids constitutes the acid challenge that humans more routinely face. Intake of acid-producing amino acids increases systemic acid production and urine net acid excretion (6), but its effect on distal nephron acidification or its hormonal and/or transport mediators are not known. Recognizing that ET ...

Specific functions served by the various Na+-K+-ATPase α-isoforms are likely to originate in regions of structural divergence within their primary structures. The isoforms are nearly identical, with the exception of the NH2 terminus and a 10-residue region near the center of each molecule (isoform-specific region; ISR). Although the NH2 terminus has been clearly identified as a source of isoform functional diversity, other regions seem to be involved. We investigated whether the central ISR could also contribute to isoform variability. We constructed chimeric molecules in which the central ISRs of rat α1- and α2-isoforms were exchanged. After stable transfection into opossum kidney cells, the chimeras were characterized for two properties known to differ dramatically among the isoforms: their K+ deocclusion pattern and their response to PKC activation. Comparisons with rat full-length α1- and α2-isoforms expressed under the same conditions suggest an involvement of the central ISR in the response to PKC but not in K+ deocclusion.

We describe two unrelated cases of ornithine aminotransferase (OAT) deficiency with rare neonatal presentation of hyperammonaemia. The diagnosis in the neonatal presentation of OAT deficiency is hampered as hyperornithinaemia is absent. Enzyme and mutation studies confirmed the diagnosis. OAT deficiency should be included in differential diagnosis of neonatal hyperammonaemia.

The Na,K-pump (i.e., Na,K-ATPase) is critical for maintaining the ionic gradients across the plasma membranes of animal cells. Its component subunits are expressed in multiple forms, but the physiological relevance of this subunit diversity remains unknown. The primary contributor to overall catalysis, the alpha subunit, exists in four isoforms. There are observed kinetic differences among these isoforms, but their subtlety makes them an unlikely basis for physiological significance. Instead, recent work suggests that the major functional distinction among the isoforms is their interaction with regulatory proteins. Moreover, the isoform-specific effects of modulatory agents such as protein kinase C seem to originate within two regions of structural divergence: the amino terminus and eleven residues near the center of the alpha subunit, the isoform-specific region.