Sodium tetraborate decahydrate

Ceramide-1-phosphate (N-hexadecanoyl-D-erythro-sphingosine-1-phosphate) was purchased from Matreya, LLC (PA, USA). EDTA (≥99.4%), NaCl (≥99.5%), NaOH (≥99.5%), CaCl₂ (≥99%) and HCl were purchased from Sigma Aldrich GmbH (Taufkirchen, Germany). Chloroform (≥99.9%) and citric acid monohydrate (≥99.5%) were purchased from Carl Roth GmbH (Karlsruhe, Germany) and methanol (≥99.9%) from VWR Chemicals (Fontenay-sous-Bois, France). Sodium tetraborate decahydrate (≥99.5%) was purchased from Merck KGaA (Darmstadt, Germany). NaCl was heated to 600 °C to remove potential organic impurities. All other chemicals and salts were used without further purification. For monolayer experiments, Milli-Q Millipore water with a specific resistance of 18.2 MΩ·cm and pH approx. 6.2 was used.

For semi-thin sectioning, kidneys were fixed by vascular perfusion with 3% PFA as described above and postfixed in the same fixative to which 1% glutaraldehyde was added. The tissue was embedded in epoxy resin (EPON) and semi-thin sections of 0.8 μm were cut with an ultramicrotome (Leica UltraCut E ultramicrotome). For staining, slides were incubated at 60 °C for 2 min in 0.5% toluidine blue (Merck, 11593) and 0.5% sodium tetraborate decahydrate (Sigma-Aldrich, S9640), diluted in water, followed by coverslip mounting with Entellan new (Merck 1079610100).

Amicon ultra centrifugal filter units (molecular weight cutoff [MWCO] 30 kDa), dimethyl sulfoxide, potassium phosphate monobasic, potassium phosphate dibasic, sodium tetraborate decahydrate, sodium acetate, o-pthaldialdehyde, 2-mercaptoethanol, and deuterium oxide were purchased from Sigma Aldrich (Oakville, Canada). α-Methoxy, ω-succinimidyl carboxymethyl ester poly(ethylene glycol) (mPEG–NHS; 5 kDa) and α-maleimide, ω-succinimidyl carboxymethyl ester PEG (Mal–PEG–NHS; 5 kDa) were purchased from JenKem Technology (Plano, USA). Aspartate Aminotransferase Activity Assay Kits were purchased from Abcam (Cambridge, UK). Angiopep (TFFYGGSRGKRNNFKTEEYC; 2.4 kDa) was purchased from Zhejiang Ontores Biotechnologies (China). Mini-PROTEIN TGX Stain-Free Precast Gels (4–15% acrylamide) and Bio-Rad precision plus protein unstained standards were purchased from Bio-Rad (Saint-Laurent, Canada). BD Microtainer^® blood collection SST tubes and BD IV catheter Insyte 24GA × 0.75” YLW BX/50 were purchased from Becton Dickinson (New Jersey, USA). All buffers were prepared using MilliQ water (mean resistivity 18.2 MΩ cm). All chemicals were purchased at the highest grade possible and used as received. hrGOT (∼1 kU/mg) was used.