Benjamin Spindler

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Amino-acid transport across cellular plasma membranes depends on several parallel-functioning (co-)transporters and exchangers. The widespread transport system L accounts for a sodium-independent exchange of large, neutral amino acids, whereas the system y(+)L exchanges positively charged amino acids and/or neutral amino acids together with sodium. The(More)
Amino acid transport across cellular membranes is mediated by multiple transporters with overlapping specificities. We recently have identified the vertebrate proteins which mediate Na+-independent exchange of large neutral amino acids corresponding to transport system L. This transporter consists of a novel amino acid permease-related protein (LAT1 or(More)
 The early aldosterone-induced increase in Na reabsorption across tight epithelia is characterized by a transcription-dependent activation of epithelial Na channels (ENaC) and pumps (Na,K-ATPase). In order to contribute towards the identification of transcriptionally regulated mediators of this process, we first tested mRNAs of proteins previously suggested(More)
Chronic restriction of dietary Pi elicits an increased reabsorption of Pi in the kidney proximal tubules, which involves a stimulation of apical Na-Pi cotransport. This adaptation is in part a direct cellular response of which the mechanism(s) are poorly understood. In this study, the impact of dietary Pi restriction on the differential expression of rat(More)
The small G protein K-Ras2A is rapidly induced by aldosterone in A6 epithelia. In these Xenopus sodium reabsorbing cells, aldosterone rapidly activates preexisting epithelial Na+ channels (XENaC) via a transcriptionally mediated mechanism. In the Xenopus oocytes expression system, we tested whether the K-Ras2A pathway impacts on XENaC activity by expressing(More)
The contribution of ATP-generating systems to Na+ pump (Na+-K+-ATPase) function was studied in Xenopus laevis A6 kidney epithelia apically permeabilized with digitonin. The ouabain-inhibitable Na+ pump current (I(P)) was measured in the presence of otherwise impermeant inhibitors and/or substrates at Na+ and K+ concentrations that allowed near-maximal pump(More)
The protein mediating system L amino acid transport, AmAT-L, is a disulfide-linked heterodimer of a permease-related light chain (AmAT-L-lc) and the type II glycoprotein 4F2hc/ CD98. The Schistosoma mansoni protein SPRM1 also heterodimerizes with h4F2hc, inducing amino acid transport with different specificity. In this study, we show that the disulfide bond(More)
The aldosterone-induced increase in sodium reabsorption across tight epithelia can be divided schematically into two functional phases: an early regulatory phase starting after a lag period of 20 to 60 minutes, during which the pre-existing transport machinery is activated, and a late phase (>2.5 h), which can be viewed as an anabolic action leading to a(More)
Adrenal steroids induce an increase in transcellular Na+ reabsorption across Xenopus laevis A6 cell epithelia that requires the action of transcriptionally regulated gene products. In a previous study we identified K-ras2 as an aldosterone-upregulated mRNA in A6 epithelia. Here, we show that in vivo injection of aldosterone in Xenopus (2.5 h) increases(More)
Aldosterone receptors from rat kidney slices were utilized in a competitive binding technique to analyze the contribution of various steroids to plasma "mineralocorticoid" activity and to assess their possible role in hypertension. To consider simultaneously the plasma binding, steroids were incubated with slices in undiluted plasma; competitor activities(More)