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•Mexican guidelines recommended a dietary reference intake for fluoride of 2.45 mg/d for adult and pregnant women.•Mexico has a salt fluoridation program.•High fluoride concentrations are neurotoxic.•Median fluoride intake through foods and beverages was estimated to be 1.01 mg/d (0.73, 1.32) in a Mexican pregnancy cohort.•Higher fluoride intake from foods and beverages during pregnancy is associated with lower cognitive neurodevelopment in male offspring.

Background: Sources of fluoride exposure for Mexicans include foods, beverages, fluoridated salt, and naturally fluoridated water. There are no available data describing fluoride content of foods and beverages consumed in Mexico.Objective: To measure the content of fluoride in foods and beverages typically consumed and to compare their content to that of those from the United States and the United Kingdom.Methods: Foods and beverages reported as part of the Mexican Health and Nutrition Survey (n = 182) were purchased in the largest supermarket chains and local markets in Mexico City. Samples were analyzed for fluoride, at least in duplicate, using a modification of the hexamethyldisiloxane microdiffusion method. Value contents were compared to those from the US Department of Agriculture and UK fluoride content tables.Results: The food groups with the lowest and highest fluoride content were eggs (2.32 µg/100 g) and seafood (371 µg/100 g), respectively. When estimating the amount of fluoride per portion size, the lowest content corresponded to eggs and the highest to fast foods. Meats and sausages, cereals, fast food, sweets and cakes, fruits, dairy products, legumes, and seafood from Mexico presented higher fluoride contents than similar foods from the United States or the United Kingdom. Drinks and eggs from the United States exhibited the highest contents, while this was the case for pasta, soups, and vegetables from the United Kingdom.Conclusion: The majority of items analyzed contained higher fluoride contents than their US and UK counterparts. Data generated provide the first and largest table on fluoride content, which will be useful for future comparisons and estimations.

Geranium seemannii Peyris a perennial plant endemic to central Mexico that has been widely used for its diuretic effect, but the responsible compound of this effect is unknown as well as the mechanism by which the diuretic effect is achieved. Geraniin is one of the compounds isolated from this kind of geranium. This study was designed to determinate whether geraniin possesses diuretic activity and to elucidate the mechanism of action. Geraniin was extracted and purified from Geranium seemannii Peyr. Male Wistar rats were divided into four groups: 1) Control, 2) 75 mg/kg of geraniin, 3) 20 mg/kg of furosemide, and 4) 10 mg/kg of hydrochlorothiazide. Each treatment was administered by gavage every 24 h for 7 days. The urinary excretion of electrolytes and the fractional excretion of sodium (FENa) were determined. To uncover the molecular target of geraniin, Xenopus laevisoocytes were microinjected with cRNAs encoding the Na+-Cl−cotransporter (NCC) and the Na+-K+-2Cl−cotransporter NKCC2 to functionally express these cotransporters. Geraniin significantly increased diuresis, natriuresis, and calciuresis to a similar extent as was observed in the furosemide-treated rats. Consistent with the furosemide-like effect, in X. laevisoocytes, geraniin significantly reduced the activity of NKCC2, with no effect on NCC activity. In contrast to furosemide, the effect of geraniin on NKCC2 was irreversible, apparently due to its inhibitory effect on heat shock protein 90. Our observations suggest that geraniin could have a potential role in the treatment of hypertension or edematous states.

K+-Cl−cotransporter (KCC) isoforms 3 (KCC3) and 4 (KCC4) are expressed at the basolateral membrane of proximal convoluted tubule cells, and KCC4 is present in the basolateral membrane of the thick ascending loop of Henle's limb and α-intercalated cells of the collecting duct. Little is known, however, about the physiological roles of these transporters in the kidney. We evaluated KCC3 and KCC4 mRNA and protein expression levels and intrarenal distribution in male Wistar rats or C57 mice under five experimental conditions: hyperglycemia after a single dose of streptozotocin, a low-salt diet, metabolic acidosis induced by ammonium chloride in drinking water, and low- or high-K+diets. Both KCC3 mRNA and protein expression were increased during hyperglycemia in the renal cortex and at the basolateral membrane of proximal tubule cells but not with a low-salt diet or acidosis. In contrast, KCC4 protein expression was increased by a low-sodium diet in the whole kidney and by metabolic acidosis in the renal outer medulla, specifically at the basolateral membrane of α-intercalated cells. The increased protein expression of KCC4 by a low-salt diet was also observed in WNK4 knockout mice, suggesting that upregulation of KCC4 in these circumstances is not WNK4 dependent. No change in KCC3 or KCC4 protein expression was observed under low- or high-K+diets. Our data are consistent with a role for KCC3 in the proximal tubule glucose reabsorption mechanism and for KCC4 in salt reabsorption of the thick ascending loop of Henle's loop and acid secretion of the collecting duct.

The SLC12A6gene encoding the K+-Cl−cotransporter KCC3 is expressed in multiple tissues, including kidney. Here, we report the molecular characterization of several NH2-terminal isoforms of human and mouse KCC3, along with intrarenal localization and functional characterization in Xenopus laevisoocytes. Two major isoforms, KCC3a and KCC3b, are generated by transcriptional initiation 5′ of two distinct first coding exons. Northern blot analysis of mouse tissues indicates that KCC3b expression is particularly robust in the kidney, which also expresses KCC3a. Western blotting of mouse tissue using an exon 3-specific antibody reveals that the kidney is also unique in expressing immunoreactive protein of a lower mass, suggestive evidence that the shorter KCC3b protein predominates in kidney. Immunofluorescence reveals basolateral expression of KCC3 protein along the entire length of the proximal tubule, in both the mouse and rat. Removal of the 15-residue exon 2 by alternative splicing generates the KCC3a-x2M and KCC3b-x2M isoforms; other splicing events at an alternative acceptor site within exon 1a generate the KCC3a-S isoform, which is 60 residues shorter than KCC3a. This variation in sequence of NH2-terminal cytoplasmic domains occurs proximal to a stretch of highly conserved residues and affects the content of putative phosphorylation sites. Kinetic characterization of KCC3a in X. laevisoocytes reveals apparent Kms for Rb+and Cl−of 10.7 ± 2.5 and 7.3 ± 1.2 mM, respectively, with an anion selectivity of Br−> Cl−> PO4= I−= SCN−= gluconate. All five NH2-terminal isoforms are activated by cell swelling (hypotonic conditions), with no activity under isotonic conditions. Although the isoforms do not differ in the osmotic set point of swelling activation, this activation is more rapid for the KCC3a-x2M and KCC3a-S proteins. In summary, there is significant NH2-terminal heterogeneity of KCC3, with particularly robust expression of KCC3b in the kidney. Basolateral swelling-activated K+-Cl−cotransport mediated by KCC3 likely functions in cell volume regulation during the transepithelial transport of both salt and solutes by the proximal tubule.

Several members of the cation-chloride cotransporter (solute carrier family 12, SLC12) gene family are expressed within the central nervous system, with one family member, the K+-Cl−cotransporter KCC2, exclusive to neurons. These transporters are best known for their roles in cell volume regulation and epithelial salt transport, but are increasingly receiving attention in neuroscience. In particular, intracellular chloride activity and hence the neuronal response to GABA and glycine appears to be determined by a balance between chloride efflux and influx through KCC2 and the Na+-K+-2Cl−cotransporter NKCC1, respectively. This relationship has important implications for neuronal development, sensory perception, neuronal excitability, and the response to neuronal injury. Finally, the association between loss of function in the K+-Cl−cotransporter KCC3, with a severe peripheral neuropathy associated with agenesis of the corpus callosum, has revealed an unexpected role for K+-Cl−cotransport in the development and/or maintenance of both the central and peripheral nervous systems.

We report the molecular and functional characterization of murine Slc26a6, the putative apical chloride-formate exchanger of the proximal tubule. The Slc26a6 transcript is expressed in several tissues, including kidney. Alternative splicing of the second exon generates two distinct isoforms, denoted Slc26a6a and Slc26a6b, which differ in the inclusion of a 23-residue NH2-terminal extension. Functional comparison with murine Slc26a1, the basolateral oxalate exchanger of the proximal tubule, reveals a number of intriguing differences. Whereas Slc26a6 is capable of Cl−, SO42−, formate, and oxalate uptake when expressed in Xenopus laevisoocytes, Slc26a1 transports only SO42−and oxalate. Measurement of intracellular pH during the removal of extracellular Cl−in the presence and absence of HCO3−indicates that Slc26a6 functions as both a Cl−/HCO3−and a Cl−/OH−exchanger; simultaneous membrane hyperpolarization during these experimental maneuvers reveals that HCO3−and OH−transport mediated by Slc26a6 is electrogenic. Cis-inhibition and efflux experiments indicate that Slc26a6 can mediate the exchange of both Cl−and SO42−with a number of substrates, including formate and oxalate. In contrast, SO42−and oxalate transport by Slc26a1 are mutually cis-inhibited but activated significantly by extracellular halides, lactate, and formate. The data indicate that Slc26a6 encodes an apical Cl−/formate/oxalate and Cl−/base exchanger and reveal significant mechanistic differences between apical and basolateral oxalate exchangers of the proximal tubule.

AbstractBackground/Aims:Several lines of evidence support that the kidney is involved in the increase of arterial blood pressure, and some genetic studies suggest that the thiazide-sensitive Na+:Cl–cotransporter could be implicated in the development of hypertension. In the present study, we analyzed the Na+:Cl–cotransporter mRNA levels in the kidney during the development of hypertension in three experimental models. Methods:The first model included 18 spontaneously hypertensive rats studied at 4, 10, and 16 weeks of age. The second model included 28 Wistar rats with two-kidney, one-clip Goldblatt hypertension studied at 7, 14, 21, and 28 days. The third model included 6 Wistar rats treated with NG-nitro-L-arginine methyl ester during 10 days. Respective controls were studied for all models. At the end of each experimental period, the systolic blood pressure was measured in the tail by plethysmography. Individual renal cortex total RNA was extracted, and the mRNA levels of the thiazide-sensitive Na+:Cl–cotransporter were assessed following a semiquantitative RT-PCR strategy. Results:All experimental models developed systemic hypertension. However, the level of mRNA expression of the Na+:Cl–cotransporter did not change in any of the models studied as compared with their respective controls. Conclusion:Our results suggest that a change in mRNA levels of the thiazide-sensitive Na+:Cl–cotransporter is not associated with the development of hypertension in spontaneously hypertensive rats, in rats with renovascular hypertension, nor in rats with hypertension induced by nitric oxide synthesis inhibition.Copyright © 2001 S. Karger AG, Basel

The K+-Cl−cotransporters (KCCs) are members of the cation-chloride cotransporter gene family and fall into two phylogenetic subgroups: KCC2 paired with KCC4 and KCC1 paired with KCC3. We report a functional comparison in Xenopusoocytes of KCC1 and KCC4, widely expressed representatives of these two subgroups. KCC1 and KCC4 exhibit differential sensitivity to transport inhibitors, such that KCC4 is much less sensitive to bumetanide and furosemide. The efficacy of these anion inhibitors is critically dependent on the concentration of extracellular K+, with much higher inhibition in 50 mmK+versus2 mmK+. KCC4 is also uniquely sensitive to 10 mmbarium and to 2 mmtrichlormethiazide. Kinetic characterization reveals divergent affinities for K+(Kmvalues of ∼25.5 and 17.5 mmfor KCC1 and KCC4, respectively), probably due to variation within the second transmembrane segment. Although the two isoforms have equivalent affinities for Cl−, they differ in the anion selectivity of K+transport (Cl−> SCN−= Br−> PO4−3> I−for KCC1 and Cl−> Br−> PO4−3= I−> SCN−for KCC4). Both KCCs express minimal K+-Cl−cotransport under isotonic conditions, with significant activation by cell swelling under hypotonic conditions. The cysteine-alkylating agent N-ethylmaleimide activates K+-Cl−cotransport in isotonic conditions but abrogates hypotonic activation, an unexpected dissociation of N-ethylmaleimide sensitivity and volume sensitivity. Although KCC4 is consistently more volume-sensitive, the hypotonic activation of both isoforms is critically dependent on protein phosphatase 1. Overall, the functional comparison of these cloned K+-Cl−cotransporters reveals important functional, pharmacological, and kinetic differences with both physiological and mechanistic implications.