Morphometrical analysis of the gap-junctional area in parenchymal cells of the rat liver after administration of dibutyryl cAMP and aminophylline

Summary In view of the presumed involvement of gap junctions in the coordination of metabolic activities, the influence of cAMP as a regulatory signal of cell metabolism on gap junctions of hepatocytes has been examined. Male rats received two intraperitoneal doses of 10 mg dibutyryl cAMP/100 g body weight with a time interval of 2.5 h and were decapitated 2.5 h later. After this 5-h interval, analysis of freeze-fracture replicas of fixed liver tissue revealed an increase in the mean (± SEM) gap-junctional membrane portion on the lateral hepatocyte membranes from 0.049 + 0.003 (n = 66) in controls to 0.061 ± 0.003 (n = 70) in treated rats, while the configuration of the connexons appeared unaltered. This effect could not be reinforced by prior administration of aminophylline: the relative gapjunctional area is similarly extended from 0.054 ± 0.003 (n = 126) in the control group to 0.065 ± 0.004 (n = 105) in the experimental animals. Probing for the time course of the junctional response, a group of rats was sacrificed 3 h after the onset of treatment. Already within this time, the gapjunctional area is augmented from 0.042 ± 0.004 (n = 63) in the concurrent controls to 0.069 ± 0.006 (n = 42) in the treated rats. These statistically significant increases in area may suggest a stimulating effect of cAMP on gap junctions of hepatocytes in vivo.This investigation was supported by grant No. 3.0059.81 (to D.W.S.) from the Fund for Medical Scientific Research (Belgium)     

Microspectrofluorimetric analysis of the formaldehyde-induced fluorophores of 5-hydroxytryptamine and dopamine in intrapulmonary neuroepithelial bodies after administration ofl-hydroxytryptophan andl-DOPA

Summary To demonstrate the intracellular store of 5-hydroxytryptamine and dopamine in pulmonary neuroepithelial bodies of the neonatal rabbit after treatment with the corresponding amino-acid precursorsl-5-hydroxytryptophan orl-3,4-dihydroxyphenylalanine, formaldehyde-induced flourescence in combination with microspectrofluorimetric analysis has been used. Emission spectra and excitation spectra in an extended wavelength range from 240 to 460 nm, the displacement of excitation peaks after exposure to hydrochloric acid vapour, and calculation of peak ratio values 410/260, 380/320, 320/260 for phenylethylamine fluorophores and 385/315 for indolylethylamine fluorphores were performed. Thus, the presence of 5-hydroxytryptamine without occurrence of 5-hydroxytryptophan was demonstrated in pulmonary neuroepithelial bodies after administration of the corresponding biological precursor, while dopamine combined with 5-hydroxytryptamine were clearly revealed after administration ofl-3,4-dihydroxyphenylalanine. The rate of photodecomposition always corroborated these findings.Dedicated to Prefessor Dr. T.H. Schiebler on the occasion of his 65th birthdaySupported by grant nr. 3.0059.81 (to D.W.S.) from the Fund for Medical Scientific Research (Belgium)     

Serum immunoassay of a small cell lung cancer associated ganglioside: development of a sensitive scintillation proximity assay

We here report an enzyme linked immunosorbent assay (ELISA) and a scintillation proximity assay (SPA) for detection of the ganglioside FucGM₁ in sera from small cell lung cancer (SCLC) patients. The SPA was more sensitive and reproducible than the ELISA. In this assay, monoclonal antibodies specific for FucGM₁ were bound to SPA particles and incubated with labelled FucGM₁ and 100 µl test-serum overnight, and counted in a -counter. The sensitivity was 0.2 ng. Seven out of twenty sera from SCLC patients were positive, whereas none of twenty sera from healthy individuals were positive for FucGM₁. The SPA was more sensitive than the previously reported HPTLC as well as a direct ELISA.Abbreviations MAb monoclonal antibody - SPA scintillation proximity assay - HPTLC high performance thin layer chromatography - SCLC small cell lung cancer - FucGM₁ Fuc1-2Gal1-3GalNAc1-4(NeuAc2-3)-Gal1-4Glc1-1Cer - ELISA enzyme linked immunosorbent assay - FCS foetal calf serum - PBS phosphate buffered saline     

Three-dimensional organization and topographical features of the myenteric plexus (Auerbach) in the porcine small intestine: scanning electron microscopy after enzymatic digestion and HCl-hydrolysis

The present scanning electron microscopical (SEM) study was initiated to visualize the surface topography of Auerbach's plexus in the ileum of the pig. After enzymatic digestion of the connective-tissue components of the tunica muscularis and the tunica serosa followed by glutaraldehyde fixation, HCl-hydrolysis and stripping off either the longitudinal or circular smooth muscle layer, the three-dimensional architecture and topographical features of the myenteric plexus can clearly be observed. In this way, ganglia, primary, secondary and tertiary strands, and single nerve fibres can be demonstrated. Individual nerve cells, which are incompletely covered by glial cells and by remnants of the basal lamina, can be recognized in the centre and periphery of the ganglia and adjacent to primary and secondary nerve strands.     

Haemolysis of rabbit erythrocytes by a lectin from the seeds of<Emphasis Type="Italic">Croton tiglium</Emphasis>

The kinetics of haemolysis of rabbit erythrocytes byCroton tiglium lectin was studied as a function of concentration of the lectin and erythrocytes. The length of the prelytic period decreased with increasing lectin concentrations, indicating that the secondary events at the membrane which follow the binding of the lectin to cell surface carbohydrate receptors are accelerated at higher surface concentrations of the lectin. The rate or extent of haemolysis was not affected by the inclusion of ions like K⁺, Ca²⁺ and Mg²⁺ in the medium or by the substitution of ionic medium by a non-ionic medium. The inhibition of haemagglutination and haemolysis of rabbit red cells byCroton tiglium lectin by antilectin rabbit serum was observed. A possible mechanism of haemolysis by the lectin is discussed.     

Plant lectins specific for N-acetyl-β-D-galactosamine

N-Acetyl-D-galactosamine in β-linkage being ubiquitous in cell surface glycoproteins, their interaction with lectins specific for this sugar moiety may be a significant event in cell adhesion phenomena. This article discusses the common β-N-acetyl galactosamine-specific lectins, with particular stress on the lectin from winged beans (Psophocarpus tetragonolobus).     

Demonstration of an “Excitation-Contraction Recoupling” Mechanism in Mammalian Ventricular Myocardium

A PROCESS called “excitation-contraction coupling” has been generally accepted to take place only in the direction of excitation to contraction. Through this mechanism a propagated action potential initiates an active state in skeletal or cardiac muscle and the muscle contracts. We propose that, in the mammalian ventricular myocardium at least, the process is not unidirectional and an important reverse coupling between the contractile system and the excitable plasma membrane has been overlooked. Through this feedback interaction the mode of contraction (that is, isotonic or isometric) not only determines the instantaneous electrical state of the plasma membrane, but also influences the mechanical events of the subsequent beats. Thus when Kaufmann et al.¹ recorded intracellular action potentials from cat papillary muscle, the time course of the repolarization was altered depending on the mode of contraction. Some kind of contraction-excitation feedback has also been suggested by Stauch² and Lab^3,4. They showed a difference in the shape of the monophasic action potential, as recorded by a suction electrode, when comparing isotonic and isovolumic contraction of the intact ventricle. But their experimental conditions did not allow satisfactory analysis of the phenomenon.