•,+ AT and y + -LAT1 in the small intestine explains the reduced intestinal absorption of some amino acid in patients with cystinuria or lysinuric protein intolerance.

No abstract

Reabsorption of phosphate in the proximal tubule is mainly mediated by the type IIa Na(+)/P(i) cotransporter (NaPi-IIa) and tightly regulated by a variety of factors including dietary phosphate intake and parathyroid hormone (PTH). PTH signals through both apical and basolateral PTH receptors and induces the rapid internalization and subsequent degradation of NaPi-IIa. At least two signalling cascades can be activated by PTH: the PLC/PKC and the cAMP/PKA pathways. Recent evidence from OK cell culture suggested the involvement of MAPK kinases in the PTH action. Here we used freshly isolated coronal mouse kidney slices and incubated them in a physiological buffer in the absence and presence of PTH with inhibitors and activators of the various signalling cascades to further study the events leading to internalization of NaPi-IIa. No alterations in the pattern of immunostaining for alpha-tubulin, actin and several brush border membrane proteins demonstrated intactness of the slices over the experimental period. Application of PTH (100 nM) induced a strong decrease of NaPi-IIa brush border staining and internalization after 45 min of incubation. The localization of the Na(+)/sulphate cotransporter (NaSi), however, was not affected. The internalization of NaPi-IIa could be completely prevented by the PKC inhibitor chelerythrine (1 micro M) or the MAPK-kinase (ERK1/2) inhibitor PD098059 (20 micro M). Without PTH both inhibitors alone had no effect. PTH induced phosphorylation of the ERK1/2 MAPK-kinases which was prevented by PD 098059. Separate activation of the cAMP/PKA pathway by 8-Br-cAMP was completely prevented by PD098059 whereas activation of the PLC/PKC pathway by the PKC activator 1,2-dioctanoyl-sn-glycerol (DOG) and the PKG pathway by 8-Br-cGMP induced internalization of NaPi-IIa which could be only partly blocked by PD 098059. Inhibition by SB203580 or activation by anisomycin of the p38 kinase pathway had no influence on NaPi-IIa localization under control conditions or after PTH stimulation. Furthermore, the PTH-induced decrease in NaPi-IIa protein could be reduced by PD 098059. These results suggest that the ERK1/2 MAPK kinase pathway plays a central role in the signalling of PTH leading to specific internalization and subsequent degradation of the type II NaPi-IIa cotransporter in the proximal tubule.

No abstract

No abstract

The kidney plays a major role in acid-base homeostasis by adapting the excretion of acid equivalents to dietary intake and metabolism. Urinary acid excretion is mediated by the secretion of protons and titratable acids, particularly ammonia. NH(3) is synthesized in proximal tubule cells from glutamine taken up via specific amino acid transporters. We tested whether kidney amino acid transporters are regulated in mice in which metabolic acidosis was induced with NH(4)Cl. Blood gas and urine analysis confirmed metabolic acidosis. Real-time RT-PCR was performed to quantify the mRNAs of 16 amino acid transporters. The mRNA of phosphoenolpyruvate carboxykinase (PEPCK) was quantified as positive control for the regulation and that of GAPDH, as internal standard. In acidosis, the mRNA of kidney system N amino acid transporter SNAT3 (SLC38A3/SN1) showed a strong induction similar to that of PEPCK, whereas all other tested mRNAs encoding glutamine or glutamate transporters were unchanged or reduced in abundance. At the protein level, Western blotting and immunohistochemistry demonstrated an increased abundance of SNAT3 and reduced expression of the basolateral cationic amino acid/neutral amino acid exchanger subunit y(+)-LAT1 (SLC7A7). SNAT3 was localized to the basolateral membrane of the late proximal tubule S3 segment in control animals, whereas its expression was extended to the earlier S2 segment of the proximal tubule during acidosis. Our results suggest that the selective regulation of SNAT3 and y(+)LAT1 expression may serve a major role in the renal adaptation to acid secretion and thus for systemic acid-base balance.

While the relationship between psychopathic personality traits and substance use has received some attention (Hart & Hare, 1989; Smith & Newman, 1990), gender differences have not been thoroughly assessed. The current study examined whether gender modified the relationship between two criminally-relevant constructs, a) psychopathy and its factors and b) drug use. A sample of 318 participants with criminal histories and recent substance use was assessed for psychopathy using the Psychopathy Checklist: Screening Version and for illicit drug use using the Structured Clinical Interview for the Diagnostic and Statistical Manual of Mental Disorders. As expected, the impulsive-antisocial traits (Factor 2) of psychopathy were positively related to a number of drug use characteristics (symptoms, age of drug initiation, extent of drug experimentation), whereas the interpersonal-affective traits (Factor 1) showed a negative relationship with drug abuse symptoms and a positive relationship with age of first use. In terms of gender differences, analyses revealed that women showed a stronger association between Factor 1 traits and later age of initiation compared to men, and that Factor 2, and antisocial facet in particular, were more strongly related to drug abuse in women than men. These findings suggest that psychopathic traits serve as both protective (Factor 1) and risk (Factor 2) correlates of illicit drug use, and in women, Factor 1 may be especially protective in terms of initiation. These conclusions add to the growing literature on potential routes to substance use and incarceration in women.

Vacuolar H⁺-ATPase are multi-subunit containing pumps important for several processes along the nephron such as receptor mediated endocytosis, acidification of intracellular organelles, bicarbonate reabsorption and secretion, and H⁺- extrusion. Mutations in the human a4 (ATP6V0A4) subunit cause distal renal tubular acidosis (dRTA). There are 4 known isoforms of the ‘a’ subunit (a1-a4). Here we investigated the expression and localization of all four isoforms in mouse kidney. Real-time PCR detected mRNAs encoding all four ‘a’ isoforms in mouse kidney with a relative abundance in the following order: a4>a2=a1>a3. Immunolocalization demonstrated expression of all ‘a’ subunits in the proximal tubule and in the intercalated cells of the collecting system. In intercalated cells a1 and a4 isoforms appeared on both the apical and basolateral side and were expressed in all subtypes of intercalated cells. In contrast, a2, and a3 were only found in the apical membrane. a1 and a4 were colocalized in the same cells with AE1 or pendrin, whereas a2 was only found in AE1 positive cells but absent from pendrin expressing intercalated cells. These results suggest that vacuolar H⁺-ATPases containing different ‘a’ isoforms may serve specific and distinct functions and may help explaining why loss of the a4 isoform causes only dRTA without an apparent defect in the proximal tubule.