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Biomedical subjects

J W Lynch

Publications and source records attributed to J W Lynch.

At least 73 records · Page 4Linked to original sources
PubMed1996

Calcium-dependent modulation of the agonist affinity of the mammalian olfactory cyclic nucleotide-gated channel by calmodulin and a novel endogenous factor.

The calcium-dependent modulation of the affinity of the cyclic nucleotide-gated (CNG) channels for adenosine 3',5'-cyclic monophosphate (cAMP) was studied in enzymatically dissociated rat olfactory receptor neurons, by recording macroscopic cAMP-activated currents from inside-out patches excised from their dendritic knobs. Upon intracellular addition of 0.2 mM Ca2+ (0.2 Ca) the concentration of cAMP required for the activation of half-maximal current (EC50) was reversibly increased from 3 microM to about 30 microM. This Ca2+-induced affinity shift was insensitive to the calmodulin antagonist, mastoparan, was abolished irreversibly by a 2-min exposure to 3 mm Mg2+ + 2 mm EGTA (Mg + EGTA), and was not restored by the application of calmodulin (CAM). Addition of CAM plus 0.2 mM Ca2+ (0.2 Ca + CAM), further reversibly shifted the cAMP affinity from 30 microM to about 200 microM. This affinity shift was not affected by Mg + EGTA exposure, but was reversed by mastoparan. Thus, the former Ca2+-only effect must be mediated by an unknown endogenous factor, distinct from CAM. Removal of this factor also increased the affinity of the channel for CAM. The affinity shift induced by Ca2+-only was maintained in the presence of the nonhydrolyzable cAMP analogue, 8-bromo-cAMP and the phosphatase inhibitor, microcystin-LR, ruling out modulation by phosphodiesterases or phosphatases. Our results indicate that the olfactory CNG channels are modulated by an as yet unidentified factor distinct from CAM.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1996

Stevens-Johnson syndrome resulting from whole-brain radiation and phenytoin.

Phenytoin, one of the most widely prescribed anticonvulsants, and steroids are routinely utilized for seizure prophylaxis in patients with various intracranial tumors. We report a case of severe Stevens-Johnson syndrome (SJS), documented by biopsy, which occurred in a patient, with metastatic squamous cell carcinoma receiving phenytoin, whole-brain radiation therapy (WBRT), and a tapering steroid dose. The pathogenesis and implications are then briefly discussed.

Anticonvulsants↗
PubMed1996

The human glycine receptor beta subunit: primary structure, functional characterisation and chromosomal localisation of the human and murine genes.

The inhibitory glycine receptor (GlyR) is a pentameric receptor comprised of alpha and beta subunits, of which the beta subunit has not been characterised in humans. A 2106 bp cDNA, isolated from a human hippocampal cDNA library, contained an open reading frame of 497 amino acids which encodes the beta subunit of the human GlyR. The mature human GlyR beta polypeptide displays 99% amino acid identity with the rat GlyR beta subunit and 48% identity with the human GlyR alpha 1 subunit. Neither [3H]strychnine binding nor glycine-gated currents were detected when the human GlyR beta subunit cDNA was expressed in the human embryonic kidney 293 cell line. However, co-expression of the beta subunit cDNA with the alpha 1 subunit cDNA resulted in expression of functional GlyRs which showed a 4-fold reduction in the EC50 values when compared to alpha 1 homomeric GlyRs. Glycine-gated currents of alpha 1/beta GlyRs were 17-fold less sensitive than homomeric alpha 1 GlyRs to the antagonists picrotoxin, picrotoxinin and picrotin, providing clear evidence that heteromeric alpha 1/beta GlyRs were expressed. The beta subunit appears to play a structural rather than ligand binding role in GlyR function. Fluorescence in situ hybridisation was used to localise the gene encoding the human GlyR beta subunit (GLRB) to chromosome 4q32, a position syntenic with mouse chromosome 3. In situ hybridisation using the human GlyR beta subunit cDNA showed that the murine GlyR beta subunit gene (Glrb) maps to the spastic (spa) locus on mouse chromosome 3 at bands E3-F1. This is consistent with the recent finding that a mutation in the murine GlyR beta subunit causes the spa phenotype. It also raises the possibility that mutations in the human beta subunit gene may cause inherited disorders of the startle response.

Amino Acid Sequence↗
PubMed1996

A phase II trial of paclitaxel in the treatment of recurrent or metastatic soft tissue sarcomas or bone sarcomas.

The study aimed to determine the activity and toxicity of taxol in the treatment of recurrent or metastatic soft tissue sarcomas or osteosarcomas. The major findings are that five patients had stable disease after two cycles of chemotherapy but two of these patients were subsequently removed from the study at their own request. The other three patients progressed after an additional two cycles of chemotherapy. Seven patients progressed during the first two cycles and were removed from the study. One patient completed only one cycle of therapy and was deemed inevaluable for study response. There were eight episodes of grade 3 or 4 neutropenia and two episodes of grade 3 thrombocytopenia. One patient experienced grade 3 neurological toxicity and one patient grade 3 mucositis. Two patients are currently alive with progressing disease and one patient is alive with no evidence of disease after undergoing surgery and radiotherapy. The principal conclusions are that Paclitaxel is ineffective in treating recurrent or metastatic soft tissue sarcoma and osteosarcoma. Treatment at this dose is quite myelosuppressive, but toxicity is generally manageable. Further study of this agent is not justified in this setting.

Adult↗
PubMed1995

Mutations affecting the glycine receptor agonist transduction mechanism convert the competitive antagonist, picrotoxin, into an allosteric potentiator.

Contrary to its effects on the gamma-aminobutyric acid type A receptor, picrotoxin antagonism of the alpha 1 subunit of the human glycine receptor is shown to be competitive, not use-dependent, and nonselective between the picrotoxin components, picrotin, and picrotoxinin. Competitive antagonism and non-use dependence are consistent with picrotoxin binding to a site in the extracellular domain. The mutations Arg-->Leu or Arg-->Gln at residue 271 of the glycine receptor alpha 1 subunit, which are both associated with human startle disease, have previously been demonstrated to disrupt the transduction process between agonist binding and channel activation. We show here that these mutations also transform picrotoxin from an allosterically acting competitive antagonist to an allosteric potentiator at low (0.01-3 microM) concentrations and to a noncompetitive antagonist at higher (> or = 3 microM) concentrations. This demonstrates that arginine 271 is involved in the transduction process between picrotoxin binding and its mechanism of action. Thus, the allosteric transduction pathways of both agonists and antagonists converge at a common residue prior to the activation gate of the channel, suggesting that this residue may act as an integration point for information from various extracellular ligand binding sites.

Allosteric Regulation↗
PubMed1995

The permeation of organic cations through cAMP-gated channels in mammalian olfactory receptor neurons.

The permeation of monovalent organic cations through adenosine 3',5'-cyclic monophosphate-(cAMP) activated channels was studied by recording macroscopic currents in excised inside-out membrane patches from the dendritic knobs of isolated mammalian olfactory receptor neurons (ORNs). Current-voltage relations were measured when bathing solution Na+ was replaced by monovalent organic cations. Permeability ratios relative to Na+ ions were calculated from changes in reversal potentials. Some of the small organic cations tested included ammonium (NH4+), hydroxylammonium and formamidinium, with relative permeability ratios of 1.41, 2.3 and 1.01 respectively. The larger methylated and ethylated ammonium ions studied included: DMA (dimethylammonium), TMA (tetramethylammonium) and TEA (tetraethylammonium) and they all had permeability ratios larger than 0.09. Even large cations such as choline, arginine and tris(hydroxymethyl)aminomethane (Tris) were appreciably permeant through the cAMP-activated channel with permeability ratios ranging from 0.19 to 0.7. The size of the permeating cations, as assessed by molecular weight, was a good predictor of the permeability. The permeability sequence of the cAMP-activated channel in our study was PNH4 > PNa > PDMA > PTMA > PCholine > PTEA. Higher permeability ratios of hydroxylammonium, arginine and tris(hydroxymethyl)aminomethane cannot be explained by ionic size alone. Our results indicate that: (i) cAMP-activated channels poorly select between monovalent cations; (ii) the pore dimension must be at least 6.5 x 6.5 A, in order to allow TEA and Tris to permeate and (iii) molecular sieving must be an important mechanism for the permeation of large organic ions through the channels with specific ion binding playing a smaller role than in other structurally similar channels. In addition, the results clearly indicate that cyclic nucleotide-gated (CNG) channels in different cells are not the same, the olfactory CNG channel being different from that of the photoreceptors, particularly with respect to the permeation of large organic cations, which the ORN channels allow to permeate readily.

Amidines↗
PubMed1995

Mutation of an arginine residue in the human glycine receptor transforms beta-alanine and taurine from agonists into competitive antagonists.

Agonist binding to the inhibitory glycine receptor (GlyR) initiates the opening of a chloride-selective channel that modulates the neuronal membrane potential. Point mutations of the GlyR, substituting Arg-271 with either Leu or Gln, have been shown to underlie the inherited neurological disorder startle disease (hyperekplexia). We show that these substitutions result in the redistribution of GlyR single-channel conductances to lower conductance levels. Additionally, the binding of the glycinergic agonists beta-alanine and taurine to mutated GlyRs does not initiate a chloride current, but instead competitively antagonizes currents activated by glycine. These findings are consistent with mutations of Arg-271 resulting in the uncoupling of the agonist binding process from the channel activation mechanism of the receptor.

Arginine↗
PubMed1995

Dietary intake of the short-chain triglyceride triacetin vs. long-chain triglycerides decreases adipocyte diameter and fat deposition in rats.

Diets containing either triacetin (the water-soluble triglyceride of acetate) or long-chain triglycerides (LCT) were fed to rats for 30 d to determine the effect on body weight gain and adipose tissue cellularity. Male Sprague-Dawley rats were allowed free access to one of three diets: a control diet containing 5% of energy as fat or one of two experimental diets that contained 30% triglyceride (by energy). The source of the triglyceride in the two experimental groups was either 100% LCT or 95% triacetin + 5% LCT. Within the experimental groups receiving 30% fat, the source of dietary triglyceride (LCT vs. triacetin) did not affect total energy consumption. There were no significant differences in body weight at the onset of the study; however, animals fed 100% LCT weighed significantly more than the other two groups at the end of the study. In all three fat pads studied, animals fed triacetin had significantly lower pad mass than did animals fed LCT. Mean fat cell size was smaller in fat depots of animals fed short-chain triglyceride. Provision of dietary energy as the short-chain triglyceride triacetin in lieu of LCT resulted in lower weight gain and fat deposition. These data demonstrate the impact of dietary triglyceride composition on body weight regulation.

Adipocytes↗
PubMed1994

Startle disease mutations reduce the agonist sensitivity of the human inhibitory glycine receptor.

The receptor for the inhibitory neurotransmitter glycine is a member of the ligand-gated ion channel receptor superfamily. Point mutations in the gene encoding the alpha 1 subunit of the glycine receptor-channel complex (GlyR) have recently been identified in pedigrees with the autosomal dominant neurological disorder, startle disease (hyperekplexia). These mutations result in the substitution of leucine or glutamine for arginine 271. This charged residue is located near the ion channel region and is predicted to affect chloride permeation through the GlyR. We found little evidence for this role from the anion/cation selectivity and lack of pronounced rectification of currents flowing through recombinant human alpha 1 subunit GlyRs containing the startle disease mutations. We reveal, however, that the startle disease mutations profoundly disrupt GlyR function by causing 230-410-fold decreases in the sensitivity of receptor currents activated by the agonist glycine. Additionally, we report corresponding 56- and 120-fold reductions in the apparent binding affinity (Ki) of glycine to the mutant GlyRs, but no change in the binding affinity of the competitive antagonist, strychnine. Thus, startle disease reduces the efficacy of glycinergic inhibitory neurotransmission by producing GlyRs with diminished agonist responsiveness. Our results show that startle disease mutations define a novel receptor activation site.

Humans↗
PubMed1994

A pertussis toxin-insensitive calcium influx mediated by neuropeptide Y2 receptors in a human neuroblastoma cell line.

Stimulation of neuropeptide Y (NPY) Y2 receptors induced an intracellular free Ca2+ ([Ca2+]i) increase in a human neuroblastoma cell line, CHP-234. When NPY in a Ca(2+)-free solution was applied, this increase was abolished. Depolarization with high KCl evoked no response, suggesting that the responses were not mediated by voltage-gated Ca2+ channels. There was no evidence that the NPY response consisted of a capacitative Ca2+ entry sensitive to internal Ca2+ store levels. The [Ca2+]i elevation was diminished by Ni2+, a blocker of Ca2+ entry. Mn2+ induced a quench of the fura-2 fluorescence, which ceased promptly upon the removal of NPY, indicating that Ca2+ entry was linked tightly to receptor activation. Although thapsigargin- and ryanodine-sensitive Ca2+ stores were present, NPY-induced responses were not impaired by pretreatment with either drug. Furthermore, NPY had no effect on the thapsigargin-sensitive store. Pertussis toxin did not affect the NPY-stimulated [Ca2+]i increase, although it abolished the NPY-dependent inhibition of cAMP production. It is concluded that the Y2 receptors couple directly to receptor-operated Ca2+ channels without the involvement of intracellular Ca2+ stores. The results also indicate that Y2 receptors can activate both pertussis toxin-sensitive and -insensitive mechanisms in the same cell.

Calcium↗
PubMed1994

Childhood and adult socioeconomic status as predictors of mortality in Finland.

Research has suggested that social-class differences in adult health may be at least partly determined by conditions earlier in life. In 2636 Finnish men, we assessed impact of childhood and adult socioeconomic conditions on adult mortality risk by examining whether differing socioeconomic life-courses from early childhood to adulthood were associated with different risks of all-cause and cardiovascular mortality. Compared with high-income adults, those with low income had increased relative risks of all-cause (2.54, 95% CI 1.83-3.53) and cardiovascular (2.37, 1.51-3.7) mortality, but these increased risks were not related in either adult group to childhood socioeconomic conditions. Men who went from low-income childhood to high-income adulthood had the same mortality risks as those whose socioeconomic circumstances were good in both childhood and adulthood (1.14, 0.56-2.31, all causes; 0.99, 0.39-2.51, cardiovascular). By contrast, men who experienced poor socioeconomic circumstances as both children and adults were about twice as likely to die as those whose position improved (2.39, 1.28-4.44, all causes; 2.02, 0.9-4.54, cardiovascular). Our findings suggest that socioeconomic conditions in childhood are not important determinants of adult health. We caution against this interpretation--a life-course approach to socioeconomic differences in adult health requires understanding of the social and economic context in which individual life-courses are determined.

Adult↗
PubMed1994

Pure red cell aplasia associated with angioimmunoblastic lymphadenopathy with dysproteinemia.

Angioimmunoblastic lymphadenopathy with dysproteinemia (AILD) can best be described as a disorder of T-cells resulting in amplification of the B-cell response and clinical symptoms of lymphadenopathy, fever, hepatosplenomegaly, and a variety of blood abnormalities. Pure red cell aplasia (PRCA), an autoimmune disorder resulting in selective aplasia of the erythroid series, has only rarely been associated with AILD. Herein we report three cases of AILD and PRCA. Serum from one patient was available for study and contained a dose-dependent inhibitor of the CFU-E but not CFU-GM cultures from normal bone marrow. This activity was found in the globulin fraction after ammonium sulfate precipitation. Patients with AILD are known to make antibodies to many autologous epitopes, and the most well-characterized mechanism of PRCA involves antibodies to red cell precursors. Our serum data are consistent with the hypothesis that such an antibody existed in our patient. Aggressive treatment of these patients resulted in transient improvement in two; however, all three died without achieving a durable complete remission with two dying of infectious complications.

Aged↗
PubMed1994

Response to radiation in chemotherapy-refractory monocytoid B-cell lymphoma: a case report.

A 39-year-old man had monocytoid lymphoma including a large retroperitoneal mass, retrocrural and porta hepatic adenopathy with localized pain, but no B symptoms. The tumor did not respond clinically or radiographically to CHOP or mini-ICE chemotherapy but has responded dramatically to radiotherapy. The patient's disease remains controlled 3 years after treatment. This case documents radioresponsiveness in a chemotherapy-refractory monocytoid lymphoma.

Adult↗
PubMed1994

A missense mutation in the gene encoding the alpha 1 subunit of the inhibitory glycine receptor in the spasmodic mouse.

Hereditary hyperekplexia, an autosomal dominant neurologic disorder characterized by an exaggerated startle reflex and neonatal hypertonia, can be caused by mutations in the gene encoding the alpha 1 subunit of the inhibitory glycine receptor (GLRA1). Spasmodic (spd), a recessive neurologic mouse mutant, resembles hyperekplexia phenotypically, and the two disease loci map to homologous chromosomal regions. Here we describe a Glra1 missense mutation in spd that results in reduced agonist sensitivity in glycine receptors expressed in vitro. We conclude that spd is a murine homologue of hyperekplexia and that mutations in GLRA1/Glra1 can produce syndromes with different inheritance patterns.

Amino Acid Sequence↗
PubMed1994

Cyclic nucleotide-gated channels of rat olfactory receptor cells: divalent cations control the sensitivity to cAMP.

cAMP-gated channels were studied in inside-out membrane patches excised from the apical cellular pole of isolated olfactory receptor cells of the rat. In the absence of divalent cations the dose-response curve of activation of patch current by cAMP had a KM of 4.0 microM at -50 mV and of 2.5 microM at +50 mV. However, addition of 0.2 or 0.5 mM Ca2+ shifted the KM of cAMP reversibly to the higher cAMP concentrations of 33 or 90 microM, respectively, at -50 mV. Among divalent cations, the relative potency for inducing cAMP affinity shifts was: Ca2+ > Sr2+ > Mn2+ > Ba2+ > Mg2+, of which Mg2+ (up to 3 mM) did not shift the KM at all. This potency sequence corresponds closely to that required for the activation of calmodulin. However, the Ca(2+)-sensitivity is lower than expected for a calmodulin-mediated action. Brief (60 s) transient exposure to 3 mM Mg2+, in the absence of other divalent cations, had a protective effect in that following washout of Mg2+, subsequent exposure to 0.2 mM Ca2+ no longer caused affinity shifts. This protection effect did not occur in intact cells and was probably a consequence of patch excision, possibly representing ablation of a regulatory protein from the channel cyclic nucleotide binding site. Thus, the binding of divalent cations, probably via a regulatory protein, controls the sensitivity of the cAMP-gated channels to cAMP. The influx of Ca2+ through these channels during the odorant response may rise to a sufficiently high concentration at the intracellular membrane surface to contribute to the desensitization of the odorant-induced response. The results also indicate that divalent cation effects on cyclic nucleotide-gated channels may depend on the sequence of pre-exposure to other divalent cations.

Animals↗
PubMed1994

The role of prognostic factors in treatment selection for early-stage Hodgkin's disease.

PURPOSE: To identify poor prognostic factors in early-stage Hodgkin's disease that predict a high rate of relapse after radiotherapy alone. MATERIALS AND METHODS: A total of 153 patients with stages I and II supradiaphragmatic Hodgkin's disease, treated between 1964 and 1986 with either radiotherapy alone (120 patients) or combined modality therapy (33 patients), were studied retrospectively to determine factors affecting freedom from relapse and absolute survival. Median follow-up was 13 years. Clinical factors were assessed by the stepwise use of a stratified log-rank test and included maximum tumor dimension in any site (< or = 6 cm or > 6 cm), age (< or = 40 or > 40), presence or absence of B symptoms, pathologic and clinical stages (I or II), number of sites involved (< or = 4 or > 4), gender, histologic subtype, and large mediastinal mass (none, small [< or = 6 cm], large [> 6 cm]). RESULTS: The only factors independently predicting a high rate of relapse were tumor dimension (> 6 cm) and number of sites (> 4 sites). At 10 years, in patients with and without the two poor prognostic factors treated with radiotherapy alone, the freedom from relapse rates were 53% and 84% (p < .0001) and the absolute survival rates were 72% and 85% (p = .004), respectively. Combined modality therapy significantly improved freedom from relapse, but not absolute survival, in patients with one or both poor prognostic factors. CONCLUSIONS: Two poor prognostic factors were identified that were highly significant in predicting a high risk of relapse after radiotherapy alone. The addition of three cycles of chemotherapy to standard radiotherapy significantly reduced the relapse rate in high-risk patients.

Combined Modality Therapy↗