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L Erb

Publications and source records attributed to L Erb.

28 records · Page 2Linked to original sources
PubMed1992

A nucleotide receptor in vascular endothelial cells is specifically activated by the fully ionized forms of ATP and UTP.

Extracellular ATP causes an increase in the concentration of cytoplasmic free calcium ([Ca2+]i) in bovine pulmonary-artery endothelial (BPAE) cells that results in the synthesis and release of prostacyclin (PGI2), a potent vasodilator and inhibitor of platelet aggregation. We show here that PGI2 release in BPAE cells correlates with the concentration of the fully ionized form of extracellular ATP (ATP4-) and not with the concentration of other ionic forms of ATP. Concentrations as low as 10 nM-ATP4- elicited an increase in PGI2 release [EC50 (concn. giving half-maximal stimulation) 3 microM] in BPAE cells incubated in an iso-osmotic medium, pH 7.4, lacking Ca2+ and Mg2+. When the pH or the Mg2+ concentration of the medium was varied so as to maintain a constant level of ATP4-, while varying the concentration of proton-ATP (HATP3-) or MgATP2- respectively, PGI2 release remained constant. An inhibitory effect of extracellular Mg2+ on PGI2 release could be attributed solely to a decrease in the concentration of ATP4-. In contrast with Mg2+, extracellular Ca2+ stimulated PGI2 release induced by ATP. Several results suggest that extracellular Ca2+ modulates PGI2 release by increasing Ca2+ uptake through an ATP(4-)-activated plasma-membrane channel. In BPAE cells incubated in Ca(2+)-free medium, ATP elicited a transient increase in [Ca2+]i that declined to the basal level within 60 s. In cells incubated in Ca(2+)-containing medium, ATP caused an increase in [Ca2+]i that had two components: a transient peak in [Ca2+]i (0-60 s) and a sustained increase in [Ca2+]i that was maintained for several minutes after ATP addition. Increasing the concentration of extracellular calcium from 0.25 mM to 10 mM had no effect on the transient rise in [Ca2+]i induced by ATP, but significantly enhanced the magnitude of the sustained increase in [Ca2+]i. Alterations in the magnitude of the sustained increase in [Ca2+]i would likely modulate PGI2 release, which was not complete until 2 min after ATP addition. Extracellular Ca2+ also stimulated PGI2 release induced by bradykinin. Bradykinin caused a sustained increase in [Ca2+]i in BPAE cells in the presence of extracellular Ca2+. Finally, the magnitude of PGI2 release induced by UTP, a more potent agonist than ATP, correlated with the concentration of extracellular fully ionized UTP (UTP4-). These findings support the hypothesis that nucleotide receptors in BPAE cells recognize the fully ionized form of ATP and UTP and are coupled to signal-transduction pathways involving the mobilization of intracellular Ca2+, the influx of extracellular Ca2+ and the subsequent release of PGI2.

Adenosine Triphosphate↗
PubMed1992

Mechanisms by which extracellular ATP and UTP stimulate the release of prostacyclin from bovine pulmonary artery endothelial cells.

Extracellular ATP and UTP caused increases in the concentration of cytoplasmic free calcium ([Ca2+]i) and the intracellular level of inositol 1,4,5-trisphosphate (IP3), a second messenger for calcium mobilization, prior to the release of prostacyclin (PGI2) from cultured bovine pulmonary artery endothelial (BPAE) cells. The agonist specificity and dose-dependence were similar for nucleotide-mediated increases in IP3 levels, [Ca2+]i and PGI2 release. An increase in [Ca2+]; and PGI2 release was observed after addition of ionomycin, a calcium ionophore, to BPAE cells incubated in a calcium-free medium. The addition of ATP to the ionomycin-treated cells caused no further increase in [Ca2+]i or PGI2 release. The inability of ATP to cause an increase in [Ca2+]i or PGI2 release in ionomycin-treated cells was apparently due to the ionomycin-dependent depletion of intracellular calcium stores since the subsequent addition of extracellular calcium caused a significant increase in both [Ca2+]i and PGI2 release. Introduction of BAPTA, a calcium buffer, into BPAE cells inhibited ATP-mediated increases in [Ca2+]i and PGI2 release, further evidence that PGI2 release is dependent upon an increase in [Ca2+]i. The increase in [Ca2+]i elicited by ATP apparently caused the activation of a calmodulin-dependent phospholipase A2 since trifluoperazine, an inhibitor of calmodulin, and quinacrine, an inhibitor of phospholipase A2, prevented the stimulation of PGI2 release by ATP. Furthermore, ATP caused the specific hydrolysis of [14C]arachidonyl-labeled phosphatidylcholine and the generation of free arachidonic acid, the rate-limiting substrate for PGI2 synthesis, prior to the release of PGI2 from BPAE cells. These findings suggest that the increase in PGI2 release elicited by ATP and UTP is at least partially dependent upon a phospholipase C-mediated increase in [Ca2+]i and the subsequent activation of a phosphatidylcholine-specific phospholipase A2. ATP analogs modified in the adenine base or phosphate moiety caused PGI2 release with a rank order of agonist potency of adenosine 5'-O-(2-thiodiphosphate) (ADP beta S) greater than 2-methylthioATP (2-MeSATP) greater than ATP, whereas alpha, beta methyleneATP and beta, gamma methyleneATP had no effect on PGI2 release.

Adenosine Triphosphate↗
PubMed1990

Covalent incorporation of 3'-O-(4-benzoyl)benzoyl-ATP into a P2 purinoceptor in transformed mouse fibroblasts.

ATP, 3'-O-(4-benzoyl)benzoyl-ATP (BzATP), a photoaffinity analog of ATP, and several other ATP analogs induced an increase in plasma membrane permeability to monovalent ions and normally impermeant metabolites, including nucleotides, in transformed 3T6 mouse fibroblasts. The rank order of agonist potency for induction of nucleotide channels was BzATP (EC50 = 15 microM) greater than ATP (EC50 = 50 microM) approximately adenosine 5'-O-(1-thiotriphosphate) (ATP alpha S) greater than 2-methylthio-ATP (EC50 = 75 microM) approximately 3'-amino-3'-deoxy-ATP greater than adenosine 5'-O-(3-thiotriphosphate) (ATP gamma S) (EC50 = 175 microM). Long wavelength UV illumination of 3T6 cells in the presence of greater than or equal to 20 microM BzATP at 4 degrees C, a nonpermeabilizing temperature, followed by removal of unbound BzATP, resulted in the efflux of 86Rb+ and the release of a prelabeled pool of cytoplasmic nucleotides when the temperature was shifted to 37 degrees C. Photoincorporation of BzATP was inhibited by ATP, ATP alpha S, ATP gamma S, and other ATP analogs that induced an increase in plasma membrane permeability to nucleotides in 3T6 cells under nonphotoactivating conditions. GTP, ITP, UTP, adenosine, and ATP analogs that did not alter plasma membrane permeability to nucleotides under nonphotoactivating conditions also had no effect on BzATP photoincorporation. Photoincorporation of BzATP occurred optimally between pH 6.6 and pH 8.2 but was inhibited at pH 6.0. Photoincorporation of BzATP was also modulated by the osmolarity and the divalent cation concentration of the assay medium. The increase in plasma membrane permeability to nucleotides induced by photoincorporated BzATP occurred at the same rate and had the same temperature, pH, ionic strength, and divalent cation requirements as the increase in plasma membrane permeability to nucleotides induced by ATP and BzATP under nonphotoactivating conditions. These findings support the hypothesis that BzATP can be covalently incorporated into a P2 purinoceptor in 3T6 cells that is coupled to plasma membrane channels for ions and other metabolites.

Adenine Nucleotides↗
PubMed1989

Permeabilization of transformed mouse fibroblasts by 3'-O-(4-benzoyl)benzoyl adenosine 5'-triphosphate and the desensitization of the process.

A photoreactive analogue of ATP, 3'-O-(4-benzoyl)benzoyl adenosine 5'-triphosphate (BzATP) altered the plasma membrane permeability of transformed 3T6 mouse fibroblasts to normally impermeant molecules as previously reported for ATP, but at lower concentrations. BzATP-induced permeabilization was modulated by pH, temperature, and the ionic composition of the medium similar to the permeabilizing effects of ATP. Conditions known to enhance ATP-induced permeabilization, such as treatment with the mitochondrial uncoupler carbonyl cyanide-m-chlorophenylhydrazone (CCCP) or the Ca2+-calmodulin antagonist trifluoperazine also enhanced BzATP-induced permeabilization. Conditions inhibitory to ATP-induced permeabilization, including chloride replacement or treatment with furosemide or dithiothreitol (DTT), inhibited permeabilization induced by BzATP. The ionic strength of the medium modulated the responsiveness of the cells to ATP and BzATP; a decrease in the ionic strength below isotonicity increased the sensitivity of the cells to the nucleotides, whereas an increase in ionic strength above isotonicity inhibited permeabilization. Prolonged exposure to ATP under non-permeabilizing conditions caused the cells to become insensitive to ATP and BzATP. The densensitization phenomenon provides support for the theory that the permeabilization process is mediated by a receptor for ATP.

Adenosine Triphosphate↗
PubMed1982

Comparison of lyophilized and frozen microtiter systems for routine MIC testing in the clinical laboratory.

Frozen microtiter plates (Micro-Media Systems, Inc.) and lyophilized microtiter plates (Sensititre--Seward Laboratory/Gibco Diagnostics) were used to perform simultaneous MIC determinations. Specimens were obtained from blood, urine and other clinical isolates. The authors found that there was good correspondence of results with the frozen microtiter MIC plates and the lyophilized microtiter MIC plates. After careful evaluation, the authors conclude that the lyophilized product is as stable and as reproducible as the frozen product. The lyophilized product is more easily and conveniently stored, has a longer shelf life and is more flexible.

Anti-Bacterial Agents↗
PubMedDate not supplied

Alcohol consumption: biochemical and personality correlates in a college student population.

The frequency of alcohol use among a subject population of 28 male and 60 female college students was assessed using the Student Alcohol and Drug Use Survey (STADUS). Data were also collected on personality traits as measured by the Sensation Seeking Scale V (SSSV) and the Eysenck Personality Questionnaire (EPQ). Finally, three biochemical variables were assessed: monoamine oxidase (MAO) activity, dopamine beta hydroxylase (DBH) activity, and testosterone levels. Among males, high SSSV scores, high testosterone levels, and low MAO activity contributed to the variance in alcohol use, whereas among females, a significant proportion of the variability in alcohol use was accounted for by high SSSV scores, high DBH activity, and younger age.

Adolescent↗