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E L Meyer

Publications and source records attributed to E L Meyer.

7 recordsLinked to original sources
PubMed2001

Granzyme B proteolysis of a neuronal glutamate receptor generates an autoantigen and is modulated by glycosylation.

Autoimmune processes are initiated when tolerance to self-proteins fails to be established or maintained and immune cells are stimulated by self-Ags. Although intracellular autoantigens are common, the origin of extracellular autoantigens is poorly defined and possibly more dangerous. In this study, we considered a mechanism for the origin of an extracellular autoantigen from the neuronal glutamate receptor subunit 3 (GluR3) in Rasmussen's encephalitis, a severe form of pediatric epilepsy. We demonstrate that specific cleavage of GluR3 by granzyme B (GB), a serine protease released by activated immune cells, can generate the GluR3B autoantigenic peptide, but only if an internal N:-linked glycosylation sequon within the GluR3-GB recognition sequence (ISND*S) is not glycosylated. However, this N:-glycon sequon while glycosylated normally is inefficiently used and glycosylation can fail. These results suggest that GB/N:-glycon sites may escape normal tolerance mechanisms and contribute to autoantibody-mediated immune diseases.

Amino Acid Sequence↗
PubMed2001

Agonist regulation of rat alpha 3 beta 4 nicotinic acetylcholine receptors stably expressed in human embryonic kidney 293 cells.

Effects of agonists on rat alpha 3 beta 4 nicotinic acetylcholine receptors expressed in KX alpha 3 beta 4R2 cells [human embryonic kidney 293-derived cells] were studied. The potencies of seven agonists varied over a 7000-fold range, with a rank order of epibatidine >> A85380 > cytisine approximately 1,1-dimethyl-4-phenyl-piperazinium iodide (DMPP) approximately nicotine > acetylcholine > carbachol. The efficacies of all of the agonists studied here were similar except for DMPP, which seemed to be a partial agonist compared with nicotine and acetylcholine. Nicotine and carbachol desensitized the receptors in a time- and concentration-dependent manner. The EC(50) values for nicotine and carbachol to desensitize the receptors during a 60-min exposure were 3 and 51 microM, respectively, indicating that these agonists are more potent at desensitizing the receptors than at activating them. The function of the receptors recovered from agonist-induced desensitization rapidly and almost completely. The half-time for recovery of function from desensitization after a 60-min treatment with nicotine increased with the concentration of nicotine used to desensitize the receptors. In contrast, no such concentration dependence for time to recovery of function was found when carbachol was used to desensitize the receptors. We propose that this difference may be due to the cell permeability of nicotine, allowing it to enter and be sequestered inside of cells and then slowly diffuse out to maintain receptor desensitization. After a 5-day exposure to 100 microM nicotine, the receptors were completely desensitized, but receptor function recovered to 83% of control values with a half-time of about 10.5 min. Although the number of nicotinic receptor binding sites measured with (+/-)-[(3)H]epibatidine was increased during the chronic treatment with nicotine, no increase in function was detected.

Animals↗
PubMed1998

Rat alpha3/beta4 subtype of neuronal nicotinic acetylcholine receptor stably expressed in a transfected cell line: pharmacology of ligand binding and function.

We stably transfected human kidney embryonic 293 cells with the rat neuronal nicotinic acetylcholine receptor (nAChR) alpha3 and beta4 subunit genes. This new cell line, KXalpha3 beta4R2, expresses a high level of the alpha3/beta4 receptor subtype, which binds (+/-)- [3H]epibatidine with a Kd value of 304+/-16 pM and a Bmax value of 8942 +/- 115 fmol/mg protein. Comparison of nicotinic drugs in competing for alpha3/beta4 receptor binding sites in this cell line and the binding sites in rat forebrain (predominantly alpha4/beta2 receptors) revealed marked differences in their Ki values, but similar rank orders of potency for agonists were observed, with the exception of anatoxin-A. The affinity of the competitive antagonist dihydro-beta-erythroidine is >7000 times higher at alpha4/beta2 receptors in rat forebrain than at the alpha3/beta4 receptors in these cells. The alpha3/beta4 nAChRs expressed in this cell line are functional, and in response to nicotinic agonists, 86Rb+ efflux was increased to levels 8-10 times the basal levels. Acetylcholine, (-)-nicotine, cytisine, carbachol, and (+/-)-epibatidine all stimulated 86Rb+ efflux, which was blocked by mecamylamine. The EC50 values for acetylcholine and (-)-nicotine to stimulate 86Rb+ effluxes were 114 +/- 24 and 28 +/- 4 microM, respectively. The rank order of potency of nicotinic antagonists in blocking the function of this alpha3/beta4 receptor was mecamylamine > d-tubocurarine > dihydro-beta-erythroidine > hexamethonium. Mecamylamine, d-tubocurarine, and hexamethonium blocked the function by a noncompetitive mechanism, whereas dihydro-beta-erythroidine blocked the function competitively. The KXalpha3 beta4R2 cell line should prove to be a very useful model for studying this subtype of nAChRs.

Animals↗
PubMed1997

Stimulation of dog RVLM and A5 area changes sympathetic outflow to vascular beds without effect on the heart.

Studies were conducted in anesthetized, vagotomized dogs while blood pressure; blood flows in femoral, renal, mesenteric, and left circumflex coronary arteries; electrocardiogram; and regional cardiac contractile force were monitored. The ventral surface of the medulla was exposed, and pressor sites in the rostral ventrolateral medulla (RVLM) were mapped by microinjections of L-glutamate. L-Glutamate activation of the RVLM evoked selective effects on different components of the cardiovascular system. Increases of 20-130 mmHg in blood pressure were accompanied by vascular conductance decreases in the femoral (-48 +/- 4%), renal (-30 +/- 4%), and mesenteric (-38 +/- 3%) arterial beds. These effects were without any obvious topography within the RVLM. There were only small or negligible changes in heart rate (HR), cardiac contractile force, and coronary vascular conductance. Thus stimulation of the canine RVLM increased sympathetic tone selectively to structures other than the heart. Stimulation of the ventral medulla in a region that lay rostral to the RVLM and ventromedial to the facial nucleus selectively increased femoral vascular conductance by 103 +/- 33% and decreased vascular conductance in the renal (-20 +/- 5%) and mesenteric (-15 +/- 4%) arterial beds. There was no increase in HR, and the increases in blood pressure were relatively small. Immunohistochemical data led us, tentatively, to identify this rostral area as overlapping part of the A5 area.

Animals↗
PubMed1993

A phase-response curve to the benzodiazepine chlordiazepoxide and the effect of geniculo-hypothalamic tract ablation.

The geniculo-hypothalamic tract (GHT) provides input to the mammalian circadian pacemaker in the suprachiasmatic nucleus. Several recent reports indicate that GHT ablation blocks phase shifts to the benzodiazepines triazolam and chlordiazepoxide at circadian times (CTs) 6 and 21. In this study we tested if GHT ablation blocks phase shifts to chlordiazepoxide at a wide range of circadian phases. Syrian hamsters were housed under constant dim light, and running-wheel activity rhythms were monitored. Intraperitoneal injections of either chlordiazepoxide (100 mg/kg) or saline were administered at various circadian times, and a phase-response curve was constructed. In intact animals, chlordiazepoxide produced phase-advance shifts at CTs 0, 4, 6, and 8, and phase-delay shifts between CTs 12-14. Although bursts of increased activity were sometimes observed on the day of injection, activity does not appear to mediate chlordiazepoxide-induced phase shifts. Hamsters with > 45% GHT ablation showed no phase shifts > 20 min to chlordiazepoxide. Our results indicate that the geniculo-hypothalamic tract is necessary for the phase-shifting effects of the benzodiazepine chlordiazepoxide throughout the circadian cycle.

Animals↗