Molecular pharmacology
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Molecular pharmacology · Nov 1995
Inhibition of succinate:ubiquinone reductase and decrease of ubiquinol in nephrotoxic cysteine S-conjugate-induced oxidative cell injury.
The role of complex II in the cellular protection against oxidative stress was investigated in freshly isolated rat renal proximal tubular cells (PTC) with the use of the nephrotoxin S-(1,2-dichlorovinyl)-L-cysteine (DCVC). DCVC caused oxidative stress in PTC as determined by flow cytometry with dihydrorhodamine-123; this fluorescent probe is readily oxidized by primary hydroperoxides such as those formed during lipid peroxidation. The oxidative stress could be prevented by inhibition of the beta-lyase-mediated formation and covalent binding to cellular macromolecules of reactive DCVC metabolites, with amino oxyacetic acid (AOA), or by the antioxidant N,N'-diphenyl-p-phenylenediamine. ⋯ The effect of DCVC on complex II was associated with a decrease in the cellular amount of reduced ubiquinone (QH2); the KCN-mediated cytoprotection was related to a 60% increase of cellular QH2. Rotenone almost completely inhibited ubiquinone reduction even in the presence of KCN, whereas oxaloacetate in combination with KCN resulted in QH2 levels comparable to control. This suggests that the SQR activity by complex II rather than the cellular content of reduced ubiquinone (QH2) is important as a part of the cellular antioxidant machinery in the cyto-protection against oxidative stress.
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Molecular pharmacology · Apr 1995
Tau phosphorylation in brain slices: pharmacological evidence for convergent effects of protein phosphatases on tau and mitogen-activated protein kinase.
Tau is a neuron-specific, microtubule-associated protein that forms paired helical filaments (PHFs) of Alzheimer's disease when aberrantly phosphorylated. We have attempted to elucidate the protein kinases and phosphatases that regulate tau phosphorylation. Incubation of rat, human, and rhesus monkey temporal neocortex slices with the phosphatase inhibitor okadaic acid induced epitopes of tau similar to those found in PHFs. ⋯ Nerve growth factor (100 ng/ml) activated p42mapk, particularly when used in combination with 100 nM okadaic acid; changes in tau mobility were seen when this kinase was activated. Forskolin (2 microM) antagonized the effects of nerve growth factor on both p42mapk activity and tau phosphorylation; forskolin alone had little effect on PHF-like tau formation induced by phosphatase inhibitors. These results outline complex interactions between tau-directed protein kinases and protein phosphatases and suggest potential sites for therapeutic intervention.
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Molecular pharmacology · Mar 1995
Signal transduction pathways for B1 and B2 bradykinin receptors in bovine pulmonary artery endothelial cells.
Bovine pulmonary artery endothelial (CPAE) cells respond to bradykinin, and it has been suggested that the receptors on these cells do not fall into the normal B1/B2 classification of bradykinin receptors [J. Pharmacol. Exp. ⋯ Pretreatment with the B1 agonist did not inhibit responses evoked by subsequent challenges with either des-Arg9-bradykinin or bradykinin. These results provide pharmacological evidence for the existence of two distinct bradykinin receptor subtypes (B1 and B2) on CPAE cells, with no evidence for heterologous desensitization. Although both subtypes operated similar signal transduction pathways, the Ca2+ responses evoked by the two receptors could be differentiated by NiCl2.
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Molecular pharmacology · Mar 1995
Chronic neurosteroid treatment produces functional heterologous uncoupling at the gamma-aminobutyric acid type A/benzodiazepine receptor complex in mammalian cortical neurons.
We have investigated the effects of chronic treatment with the neurosteroid 5 alpha-pregnan-3 alpha-ol-20-one (5 alpha 3 alpha) on the gamma-aminobutyric acid (GABA)A receptor complex in cultured mammalian cortical neurons. Chronic 5 alpha 3 alpha treatment (up to 2 microM, 5 days) did not produce any changes in the morphological appearance or the cell protein content of cortical neurons. The basal binding of [3H]flunitrazepam, [3H]Ro15-1788, and [3H]Ro15-4513 was not altered after the chronic treatment. ⋯ The EC50 value for GABA-induced 36Cl- influx was not altered, whereas the Emax value was decreased after chronic 5 alpha 3 alpha treatment. Furthermore, the 5 alpha 3 alpha-induced uncoupling was reversed by concomitant exposure of the cortical neurons to 5 alpha-pregnan-3 beta-ol-20-one or R5135, suggesting an involvement of the neurosteroid and GABA recognition sites in the observed uncoupling. Taken together, these results suggest that chronic 5 alpha 3 alpha treatment produces heterologous uncoupling at the GABAA receptor complex.
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Molecular pharmacology · Dec 1993
Structural and conformational features determining selective signal transduction in the beta 3-adrenergic receptor.
With respect to the beta 1- and beta 2-adrenergic receptors (ARs), the beta 3-AR induces specific physiological effects in a few target tissues and exhibits atypical pharmacological properties that distinguish it unambiguously from its counterparts. Therefore, the beta 3-AR represents a suitable model to study the molecular mechanism responsible for receptor subtype selectivity and specificity. Potent beta 3-AR ligands newly characterized in Chinese hamster ovary cells expressing the beta 3-AR were also evaluated in Chinese hamster ovary cells expressing beta 1- and beta 2-ARs and were classified into three groups according to their pharmacological properties. ⋯ Structure-activity relationship analysis indicates that potent or selective beta 3-AR compounds, in addition to possessing a pharmacophore common to all beta-AR ligands, contain a long and bulky alkylamine substituent moiety, which is able to adopt and exchange extended and stacked conformations. Computerized three-dimensional models of the beta 1-, beta 2-, and beta 3-AR binding sites show that more bulky amino acid side chains point inside the groove of the beta 1 and beta 2 sites, compared with the beta 3 site, in a region implicated in signal processing. The long alkylamine chain of compounds behaving as beta 1/beta 2 antagonists and beta 3 agonists may thus adopt either a stacked conformation in the encumbered beta 1- and beta 2-AR sites, leading to antagonistic effects, or an extended conformation in the less encumbered beta 3 site, thus interacting with specific residues implicated in signal transduction.