Rat Organic Cation Transporter 1 Contains Three Binding Sites for Substrate 1-Methyl-4-phenylpyridinium per Monomer.

Organic cation transporters OCT1 () and OCT2 () are critically involved in absorption and excretion of diverse cationic drugs. Because drug-drug interactions at these transporters may induce adverse drug effects in patients, in vitro testing during drug development for interaction with the human transporters is mandatory. Recent data performed with rat OCT1 (rOCT1) suggest that currently performed in vitro tests assuming one polyspecific binding site are insufficient.

Assay Conditions Influence Affinities of Rat Organic Cation Transporter 1: Analysis of Mutagenesis in the Modeled Outward-Facing Cleft by Measuring Effects of Substrates and Inhibitors on Initial Uptake.

The effects of mutations in the modeled outward-open cleft of rat organic cation transporter 1 (rOCT1) on affinities of substrates and inhibitors were investigated. Human embryonic kidney 293 cells were stably transfected with rOCT1 or rOCT1 mutants, and uptake of the substrates 1-methyl-4-phenylpyridinium (MPP) and tetraethylammonium (TEA) or inhibition of MPP uptake by the nontransported inhibitors tetrabutylammonium (TBuA), tetrapentylammonium (TPeA), and corticosterone was measured. Uptake measurements were performed on confluent cell layers using a 2-minute incubation or in dissociated cells using incubation times of 1, 5, or 10 seconds.

Protein RS1 (RSC1A1) Downregulates the Exocytotic Pathway of Glucose Transporter SGLT1 at Low Intracellular Glucose via Inhibition of Ornithine Decarboxylase.

Na-d-glucose cotransporter 1 (SGLT1) is rate-limiting for glucose absorption in the small intestine. Shortly after intake of glucose-rich food, SGLT1 abundance in the luminal membrane of the small intestine is increased. This upregulation occurs via glucose-induced acceleration of the release of SGLT1-containing vesicles from the trans-Golgi network (TGN), which is regulated by a domain of protein RS1 (RSC1A1) named RS1-Reg.

Phosphorylation of RS1 (RSC1A1) Steers Inhibition of Different Exocytotic Pathways for Glucose Transporter SGLT1 and Nucleoside Transporter CNT1, and an RS1-Derived Peptide Inhibits Glucose Absorption.

Cellular uptake adapts rapidly to physiologic demands by changing transporter abundance in the plasma membrane. The human gene RSC1A1 codes for a 67-kDa protein named RS1 that has been shown to induce downregulation of the sodium-D-glucose cotransporter 1 (SGLT1) and of the concentrative nucleoside transporter 1 (CNT1) in the plasma membrane by blocking exocytosis at the Golgi. Injecting RS1 fragments into Xenopus laevis oocytes expressing SGLT1 or CNT1 and measuring the expressed uptake of α-methylglucoside or uridine 1 hour later, we identified a RS1 domain (RS1-Reg) containing multiple predicted phosphorylation sites that is responsible for this post-translational downregulation of SGLT1 and CNT1.

Central nervous system infiltrates are characterized by features of ongoing B cell-related immune activity in MP4-induced experimental autoimmune encephalomyelitis.

In multiple sclerosis (MS) lymphoid follicle-like aggregates have been reported in the meninges of patients. Here we investigated the functional relevance of B cell infiltration into the central nervous system (CNS) in MP4-induced experimental autoimmune encephalomyelitis (EAE), a B cell-dependent mouse model of MS. In chronic EAE, B cell aggregates were characterized by the presence of CXCL13(+) and germinal center CD10(+) B cells.