In humans and terrestrial vertebrates, the kidney controls systemic pH in part by absorbing filtered bicarbonate in the proximal tubule via an electrogenic Na ؉ /HCO 3 ؊ cotransporter (NBCe1/SLC4A4). Recently, human genetics revealed that NBCe1 is the major renal contributor to this process. Homozygous point mutations in NBCe1 cause proximal renal tubular acidosis (pRTA), glaucoma, and cataracts (Igarashi, T., Inatomi, J., Sekine, T., Cha, S. H., Kanai, Y., Kunimi, M., Tsukamoto, K., Satoh, H., Shimadzu, M., Tozawa, F., Mori, T., Shiobara, M., Seki, G., and Endou, H. (1999) Nat. Genet. 23, 264 -266). We have identified and functionally characterized a novel, homozygous, missense mutation (S427L) in NBCe1, also resulting in pRTA and similar eye defects without mental retardation. To understand the pathophysiology of the syndrome, we expressed wild-type (WT) NBCe1 and S427L-NBCe1 in Xenopus oocytes. Function was evaluated by measuring intracellular pH (HCO 3 ؊ transport) and membrane currents using microelectrodes. HCO 3 ؊ -elicited currents for S427L were ϳ10% of WT NBCe1, and CO 2 -induced acidification was ϳ4-fold faster. Na ؉ -dependent HCO 3 ؊ transport (currents and acidification) was also ϳ10% of WT. Current-voltage (I-V) analysis reveals that S427L has no reversal potential in HCO 3 ؊ , indicating that under physiological ion gradient conditions, NaHCO 3 could not move out of cells as is needed for renal HCO 3 ؊ absorption and ocular pressure homeostasis. I-V analysis without Na ؉ further shows that the S427L-mediated NaHCO 3 efflux mode is depressed or absent. These experiments reveal that voltage-and Na ؉ -dependent transport by S427L-hkNBCe1 is unfavorably altered, thereby causing both insufficient HCO 3 ؊ absorption by the kidney (proximal RTA) and inappropriate anterior chamber fluid transport (glaucoma).

Hereditary hypouricemia may result from mutations in the renal tubular uric acid transporter URAT1. Whether mutation of other uric acid transporters produces a similar phenotype is unknown. We studied two families who had severe hereditary hypouricemia and did not have a URAT1 defect. We performed a genome-wide homozygosity screen and linkage analysis and identified the candidate gene SLC2A9, which encodes the glucose transporter 9 (GLUT9). Both families had homozygous SLC2A9 mutations: A missense mutation (L75R) in six affected members of one family and a 36-kb deletion, resulting in a truncated protein, in the other. In vitro, the L75R mutation dramatically impaired transport of uric acid. The mean concentration of serum uric acid of seven homozygous individuals was 0.17 Ϯ 0.2 mg/dl, and all had a fractional excretion of uric acid Ͼ150%. Three individuals had nephrolithiasis, and three had a history of exercise-induced acute renal failure. In conclusion, homozygous loss-of-function mutations of GLUT9 cause a total defect of uric acid absorption, leading to severe renal hypouricemia complicated by nephrolithiasis and exercise-induced acute renal failure. In addition to clarifying renal handling of uric acid, our findings may provide a better understanding of the pathophysiology of acute renal failure, nephrolithiasis, hyperuricemia, and gout. 21: 64 -72, 201021: 64 -72, . doi: 10.1681 In most mammals, uric acid (UA) is oxidized by the hepatic enzyme uricase to highly soluble allantoin. In humans, however, this enzyme is inactive as a result of mutational silencing, 1 making UA the end product of purine metabolism. Serum UA concentration depends on both UA production and UA removal by the kidneys and intestinal tract and is high in humans compared with other mammals. Elevation of serum UA levels has been associated with various diseases, including gout, hypertension, and cardiovascular and renal disease. 2 Conversely, it has been suggested that UA has a beneficial role as a natural antioxidant, and low serum UA levels have been linked to several neurologic diseases. 2 Studies of renal handling of UA in humans have J Am Soc Nephrol

Abstract. A heterotrimeric Gai subunit, «i-3, is localized on Golgi membranes in LLC-PKI and NRK epithelial cells where it colocalizes with mannosidase II by immunofluorescence . The M-3 was found to be localized on the cytoplasmic face of Golgi cisternae and it was distributed across the whole Golgi stack. The a;_3 subunit is found on isolated rat liver Golgi membranes by Western blotting and Gai-3 on the Golgi apparatus is ADP ribosylated by pertussis toxin. LLC-PKI cells were stably transfected with GO ;-3 on an MT1, inducible promoter in order to overexpress ai-3 on Golgi membranes. The intracellular processing and

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