The effect of concanavalin A on the rat electro-olfactogram. Differential inhibition of odorant response.

When the rat olfactory mucosa is treated with concanavalin A, it subsequently shows diminished sensitivity towards 60% of the 112 odorants tested (as judged by the amplitude of the electro-olfactogram response). Odorants containing four to six carbon atoms tend to show the largest (absolute) diminutions, suggesting a receptor for this kind of odorant, although the structural specificity is weak. The receptor seems to be of particular importance in the detection of thiols, carboxylic acids and hydrocarbons of the above size, since these compounds loose the highest proportion of their original signal. The concanavalin A appears to be binding to the glycan of one or more cell-surface proteins. The binding may be at, or close to, at least one odorant receptor.     

Concanavalin A reveals olfactory receptors which discriminate between alkane odorants on the basis of size.

For certain odorants, the amplitude of the rat electro-olfactogram is reduced if the olfactory epithelium is treated with the lectin concanavalin A. When normal and cycloalkanes of one to ten carbon atoms are used as odorants at equimolar concentration, the maximum reduction in amplitude is found to correlate with the size of the stimulus molecule. This observation is consistent with the notion that concanavalin A disables an olfactory receptor molecule which normally responds to the alkyl moiety of odorants in a particular size range. That moiety may thus represent a 'primary' quality-determining component in odour discrimination.     

Regulation of proliferation and differentiation of respiratory tract epithelial cells by TGFβ

In this paper we examined the effects of transforming growth factor β (TGFβ) on the proliferation and differentiation of rabbit tracheal epithelial cells in primary culture. Treatment of these cells with TGFβ inhibits cell proliferation in a time- and dose-dependent manner; concentrations as low as 1 pM are able to inhibit cell growth. Concomitantly, TGFβ causes cells to accumulate in the G0/G1 phase of the cell cycle and a sharp reduction in the ability of the cells to form colonies after subculture at clonal density. These results indicate that TGFβ induces terminal cell division in these cells. The inhibition of cell growth is accompanied by changes in cell morphology and a stimulation of the formation of cross-linked envelopes. TGFβ enhances the levels of transglutaminase activity and cholesterol sulfate, two markers of squamous differentiation. Our results indicate that TGFβ induces terminal squamous cell differentiation in rabbit tracheal epithelial cells. Retinoic acid (RA) does not affect the commitment to terminal cell division induced by TGFβ, but inhibits the expression of the squamous phenotype. Growth of normal human bronchial epithelial cells was affected by TGFβ in a way similar to that of rabbit tracheal epithelial cells. Several carcinoma cell lines tested were quite resistant to TGFβ, whereas growth of one carcinoma cell line was stimulated by TGFβ. These results indicate that a modified response to TGFβ could be one mechanism involved in the aberrant growth control of malignant cells.     

Behavioral treatment of irritable bowel syndrome: A 1-year follow-up study

Sixteen clients afflicted with irritable bowel syndrome (IBS) were reassessed 1 year following completion of a multicomponent treatment package incorporating progressive muscle relaxation, thermal biofeedback, cognitive therapy, and IBS education. For the 14 patients who kept a 2-week symptom diary, significant reductions in ratings of abdominal pain and tenderness, diarrhea, and flatulence were obtained comparing pretreatment and follow-up symptom-diary ratings. Eleven of 14 clients were improved over pretreatment levels, 57% met the criteria for clinical improvement of at least a 50% reduction in major symptom scores, and all but 1 of 16 rated themselves as subjectively improved.     

Subcellular distributions of calcium/calmodulin-stimulated and guanine nucleotide-regulated adenylate cyclase activities in the cerebral cortex

The subcellular distribution of Ca²⁺/calmodulin-stimulated adenylate cyclase activity was studied in comparison with that of guanine nucleotide-stimulated cyclase activity. The distributions of these activities were similar among the crude fractions but differed among the purified subsynaptosomal fractions. The specific activity of Ca²⁺/calmodulin-stimulated cyclase was highest in a light synaptic membrane fraction, which has few, if any, postsynaptic densities, whereas that of guanine nucleotide-stimulated cyclase was highest in a heavier synaptic membrane fraction rich in postsynaptic densities. These results suggest that the Ca²⁺/calmodulin-stimulated cyclase has, at least in part, a different cellular or subcellular location than the guanine nucleotide-stimulated cyclase.Abbreviations used CaM calmodulin - GppNHp guanosine 5-(,-imino) triphosphate     

Studies on the complex formed between glucagon and dicaprylphosphatidylcholine

The interaction between glucagon and dicaprylphosphatidylcholine (DCPC) was studied by fluorescence, circular dichroism and calorimetry, as well as by ¹H- and ³¹P-nuclear magnetic resonance. The water-soluble lipid-protein complex was also characterized by gel filtration and ultracentrifugation. The complex appeared to be monodisperse by sedimentation equilibrium measurements, with a molecular weight of (4.55 ± 0.57)·10⁴. This complex contained approximately 7 molecules of glucagon and 35 molecules of phospholipid. Proton-decoupled ³¹P-NMR spectra of the phospholipid in the lipid-protein complex display narrower resonances than those of sonicated vesicles of DCPC, and ¹H-³¹P coupling could be detected in proton coupled spectra. These NMR results, together with gel-filtration results, suggest that glucagon ‘solubilizes’ phospholipid aggregates, forming a lipid-protein complex which is smaller than sonicated preparations of DCPC. ¹H-NMR resonance of both the methionine methyl group (met-27) and the aromatic envelope of glucagon are broadened by the phospolipid, indicating that the C-terminal region and the aromatic residues are involved in the interaction with the phospholipid. Nuclear magnetic resonance titrations of the imidazole ring C(2) and C(4) protons of the histidine residue of glucagon show that DCPC lowers the pK of the imidazole. The alterations caused by the phospholipid in the far and near ultraviolet CD spectra of glucagon reflect, respectively, the increased helix content of the hormone and the fact that the aromatic residues are located in a more structured environment. The phospholipid also alters the fluorescence properties of glucagon, shifting the fluorescence emission maximum of the hormone to shorter wavelength, and enhancing its relative intensity. This suggests that the fluorophore is experiencing a more hydrophobic environment in the presence of the lipid. Binding of glucagon to the phospholipid was analysed by Scatchard plots of the enhancement of fluorescence caused by the phospholipid and showed that the equilibrium binding constants of glucagon to DCPC are (4.4 ± 0.5)·10⁴M^?1 and (7.5±0.5)·10⁴M^?1, at 15°C and 25°C, respectively. The average number of moles of phospholipid bound per mole of glucagon is 4.4±0.6. The isothermal enthalpy of reaction of glucagon with DCPC is ?20.5 kcal/mol of glucagon at 25°C and ?32.5 kcal/mol of glucagon at 15°C. The observed enthalpies can arise from glucagon-induced cyrstallization of the phospholipid, from the non-covalent interactions between the peptide and lipid as well as from the lipid-induced conformational change in the protein. These results demonstrate that, unlike the complexes formed between glucagon and phospholipids which form more stable bilayers, the complex formed between glucagon and DCPC is stable over a wide range of temperatures, including temperatures well above the phase transition.     

The use of acetylated cytochrome c in detecting superoxide anion production in rabbit alveolar macrophages

Polymorphonuclear phagocytes have been shown to undergo marked alteration in oxidative metabolism during phagocytosis. These alterations, collectively known as the "respiratory burst", include increased glucose oxidation through the hexose monophosphate shunt (1), increased oxygen consumption (1), and increased superoxide (O-2)3 (2) and H2O2 production (3). Similar metabolic events have also been shown to occur in the rabbit alveolar macrophage (AM). There is consistent evidence that the macrophage undergoes increased oxygen consumption (4-6) and hexose monophosphate shunt activity (4-9) upon phagocytosis. There are conflicting data, however, concerning the ability of the macrophage to produce O-2. Some studies suggest that macrophages are incapable of producing measurable amounts of O-2 upon phagocytosis (7, 10-12). Other studies, however, suggest that macrophages are indeed capable of producing substantial amounts of O-2 during phagocytosis (8, 13-15). This study was designed to resolve the discrepancies in the literature concerning O-2 production in macrophages.     

Ecdysteroids regulate the release and action of eclosion hormone in the tobacco hornworm, Manduca sexta (L.)

The relationship between the ecdysteroid titre and eclosion hormone was explored for the pupal and adult ecdyses of Manduca sexta. Ecdysteroid treatment late during either moult caused a dosedependant delay in the time of ecdysis. Sensitivity to exogenous steroid treatment dropped off as the respective moults neared completion and in both cases coincided with the time of the low point in the endogenous ecdysteroid titre. It was concluded that an ecdysteroid decline is a normal prerequisite for the ecdyses of both stages. The steroid drop is important for two aspects of the eclosion hormone system: it causes target tissues to become sensitive to the peptide and it is a prerequisite for the subsequent release of eclosion hormone itself. Thus, the dual action of the declining ecdysteroid titre insures that when eclosion hormone is released, the tissues will be competent to respond to it.