Biomedical subjects

T J Furlong

Publications and source records attributed to T J Furlong.

6 recordsLinked to original sources

PubMed1992

Molecular cloning and expression of an adenosine A2b receptor from human brain.

A novel receptor cDNA was isolated from a human hippocampal cDNA library. The encoded polypeptide contains structural features consistent with its classification as a G protein-coupled receptor and shares 45% homology with the human A1 and A2a adenosine receptors. Chinese hamster ovary K1 cells expressing this receptor showed marked stimulation of adenylate cyclase when treated with 1mM adenosine. There was no response to ligands selective for A1 and A2a receptors but the general adenosine agonist N-ethylcarboxyamidoadenosine (NECA) caused a 10 fold increase in cyclic AMP accumulation with an EC50 of approximately 0.9 microM. This effect was inhibited by the adenosine receptor antagonist theophylline. Specific binding of A1 and A2a selective agonists and NECA was not detected. It is proposed that the novel receptor is a human brain adenosine A2b receptor subtype.

Adenosine↗

PubMed1992

Molecular characterization of a human brain adenosine A2 receptor.

A cDNA encoding a G protein-coupled receptor of unknown ligand specificity was isolated from a human hippocampal cDNA library by virtue of the high degree of structural homology between members of this receptor family. The cloned receptor DNA was transfected into human embryonic kidney 293 cells. Stably transfected cell lines bound a variety of adenosine agonists and antagonists with affinities characteristic of a brain adenosine A2a receptor. The A2a specific agonist CGS21680 stimulated cAMP production but did not alter intracellular calcium concentrations in transfected 293 cells.

Adenylyl Cyclases↗

PubMed1991

Activation of osmolyte efflux from cultured renal papillary epithelial cells.

The rabbit renal papillary epithelial cell line PAP-HT25 accumulates sorbitol and other organic osmolytes when cultured in hypertonic media. When returned to isotonic media, PAP-HT25 cells swell because of water influx and then shrink to their normal volume because of rapid osmolyte and water efflux (volume regulatory decrease, VRD). Sorbitol efflux from PAP-HT25 cells during VRD was reduced to 18% of control by incubation of the cells with 100 microM eicosatetraynoic acid (ETYA), indicating that an enzyme that metabolizes arachidonic acid (AA) is a key component of the efflux process. Sorbitol efflux was unaffected by incubation with cyclooxygenase and lipoxygenase inhibitors but was reduced to 9% by incubation with 100 microM ketoconazole and to 37% by incubation with 100 microM SKF-525A, indicating that the cytochrome P-450 limb of the AA cascade is involved in the efflux process. The efflux of other organic osmolytes betaine and myoinositol, but not glycerolphosphorylcholine, was also inhibited by incubation with ETYA and ketoconazole.

Animals↗

PubMed1991

Sorbitol permease: an apical membrane transporter in cultured renal papillary epithelial cells.

The efflux of sorbitol from the rabbit papillary epithelial cell line PAP-HT25 occurs through a specific transport pathway, which we denote the "sorbitol permease." The permease was studied by measuring cell volume changes that accompanied osmotic swelling and by determination of the sorbitol efflux from plasma membrane vesicles. The cell volume studies showed that sorbitol efflux in response to hypotonicity occurred only across the apical membrane of the cells and that loss of sorbitol was the primary mechanism for regulatory volume decrease (RVD) by these cells. Quinidine, a permeant inhibitor of the sorbitol permease, was shown to prevent RVD when added to either apical or basolateral bathing solution. Cell volume experiments also showed that the permease was present only on the apical membrane of cells that had been grown in isotonic medium and did not accumulate sorbitol. The permease could be demonstrated in membrane vesicles obtained from cells exposed to a hypotonic environment before being homogenized. Quinidine blocked the sorbitol efflux from vesicles indicating that it either directly inhibited the permease or a membrane-associated activation step.

Animals↗

PubMed1990

Mechanisms underlying volume regulatory decrease by Necturus gallbladder epithelium.

Volume regulatory decrease (VRD) by Necturus gallbladder epithelial cells in Cl Ringer was unaffected by the addition of 5 mM BaCl2 to apical perfusates but was inhibited by the addition of 5 mM BaCl2 and 50 or 3 microM phencyclidine (PCP) to serosal perfusates, suggesting that K channels in the basolateral membrane were activated during VRD. VRD was unaffected by replacement of Cl with NO3 or SCN, suggesting that Cl-dependent Na-K-Cl and K-Cl cotransport were not involved. In SCN Ringer, VRD was inhibited by the addition of 0.1 mM bumetanide to serosal perfusates, suggesting that bumetanide-sensitive anion channels in the basolateral membrane were also activated. A transient 10-mV hyperpolarization of the membrane potential was associated with VRD. The channel blockers that inhibited VRD had little or no effect on the hyperpolarization, suggesting that the changes in membrane potential were unrelated to the changes in cell volume. Perfusion of the apical surface of the epithelium with isotonic solutions containing 10 mM D-glucose resulted in a variable increase in cell volume followed by a variable shrinkage to normal, suggesting that VRD was also activated during organic solute absorption. The increase in cell volume was blocked by the addition of 0.01 or 1 mM phlorizin to mucosal perfusates. The reduction in cell volume was inhibited by the addition of 0.1 mM bumetanide, but not BaCl2 or PCP, to serosal perfusates, indicating the the shrinkage mechanism secondary to glucose addition differed from that seen after exposure to hypotonic perfusates.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗

PubMed1990

D-penicillamine and the transport of L-cystine by rat and human renal cortical brush-border membrane vesicles.

Brush-border membrane vesicles (BBMV) were prepared from rat and human renal cortical tissue by magnesium aggregation and differential centrifugation, and the uptake of L-cystine, L-cysteine, and L-cysteine-D-penicillamine were assessed by a rapid-filtration technique. L-Cystine uptake was relatively sodium independent and associated with membrane binding. Sodium-stimulated uptake was sensitive to a cation but not anion diffusion potential. Both sodium-independent and sodium-stimulated uptake rates were inhibited by the cationic L-amino acids and by some neutral L-amino acids. The uptake rates of L-cysteine and L-cysteine-D-penicillamine were more sodium dependent, and sodium-stimulated uptake rates were more sensitive to cation and anion diffusion potentials. Neither the sodium-independent nor the sodium-stimulated uptake rates of L-cysteine or L-cysteine-D-penicillamine were inhibited by the cationic L-amino acids. L-Cysteine-D-penicillamine showed relatively little membrane binding. It is concluded that L-cystine is transported into renal cortical BBMV by pathways distinct from those concerned with the transport of L-cysteine and L-cysteine-D-penicillamine, and it is postulated that these differences may account for some of the effects of D-penicillamine in cystinuria.

Amino Acids↗