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At least 1,765 records · Page 98Linked to original sources
PubMed1990

Interference of recombinant eglin C, a proteinase inhibitor extracted from leeches, with neutrophil-mediated platelet activation.

Eglin C is an inhibitor of two serine proteinase-derived polymorphonuclear leucocytes (PMN) i.e., elastase and cathepsin G. Since the latter has recently been shown to be involved in the activation of platelets by stimulated PMN, the effects of recombinant eglin C in the PMN-platelet cooperation model were studied. First, the inhibitory capacity of eglin C against purified cathepsin G was measured spectrophotometrically by following hydrolysis of a specific synthetic substrate, N-succinyl-ala-ala-pro-phe-para-nitroanilide. The inhibition of the enzymatic activity of 180 nM (5 micrograms/ml) cathepsin G was directly proportional to eglin C concentration and reached 100% with 2 micrograms/ml (240 nM). Platelet activation generated by a submaximal concentration of cathepsin G (200 nM) was also totally suppressed by 2 micrograms/ml of eglin C. Inhibition was specific (a 100 times higher concentration of eglin C did not alter platelet activation induced by thrombin), and surmountable (an increase of cathepsin G concentration reduced the eglin C effect). Thus, the mechanism of inhibition by eglin C of cathepsin G-induced platelet activation could be explained by a stoichiometric relation between eglin C and cathepsin G as previously described. Investigations were then performed with the PMN-platelet cooperation model, using two distinct stimuli, N-formylmethionylleucylphenylalanine (FMLP) or recombinant human C5a, at submaximal concentrations, 2.10(-7) M and 10(-7) M, respectively. A concentration-dependent inhibition of platelet activation aggregation and serotonin release-lambda was observed. Eglin C used at 10 micrograms/ml and 25 micrograms/ml totally blocked the platelet responses induced by recombinant human C5a and FMLP, respectively. Leucotriene B4, but also thromboxane B2 production measured by radioimmunoassays, were observed under FMLP activation. In the presence of eglin C, thromboxane B2 formation was totally suppressed, whereas leucotriene B4 synthesis was still effective. In fact, the mechanism of inhibition of eglin C is located neither on PMN (leucotriene B4 formation by FMLP-activated PMN was not affected), nor on platelets (response to thrombin was unchanged). The target is most probably cathepsin G since eglin C suppressed thromboxane B2 formation by platelets challenged by this serine proteinase. These results constitute an argument in favor of the implication of cathepsin G in the PMN-mediated platelet activation. Moreover, they reinforce the hypothesis that this mechanism could be operating under in vivo pathologic conditions, since eglin C is capable of preventing or ameliorating some experimental pulmonary diseases.

Animals↗
PubMed1990

[Hydrolysis of the isopeptide epsilon-(gamma-glutamyl)-lysine by destabilase from the medicinal leech Hirudo medicinalis].

Using amino acid analysis, the ability of destabilize to hydrolyze the epsilon-(gamma-Glu)-Lys isopeptide bond was demonstrated. Incubation of the epsilon-(gamma-Glu)-Lys isopeptide with the enzyme was accompanied by a decrease of the amount of the isopeptide and an increase of equimolar amounts of lysine and glutamic acid. Complete hydrolysis of the isopeptide was observed after 96 hour incubation with destabilize. It was supposed that the isopeptide is a less specific substrate for destabilize compared to L-gamma-Glu-pNA.

Amino Acids↗
PubMed1979

[Bioelectrical activity and ultrastructure of medicinal leech Retzius neurons during chronic direct and synaptic activation].

The threshold direct or synaptic 1/sec stimulation of the Retzius cells increases the firing rate of the neuron in the leach. The firing rate becomes synchronized with the stimulation applied. The membrane potential does not change. After 10 min of such stimulation changes occurring in the ultrastructure of neuron are similar to those in a neuron with no stimulation: these changes reveal a decrease in the synthetic processes whereas the bioelectrical activity remains the same which suggests a certain independence of the neuron electrophysiological parameters of its ultrastructure.

Animals↗
PubMed1990

Use of leeches.

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Animals↗
PubMed1989

Re-development of synaptic connections after implanted single 5-HT containing neuron in isolated leech ganglia.

Single mature Retzius cells which contain 5-HT have been implanted in isolated ganglia of Whitmania pigra. The properties of the implanted Retzius cell and its connections with the original identified nerve cells of the ganglia have been measured by intracellular microelectrodes. At 3 days in culture an implanted Retzius cell maintains its normal electrical membrane properties. It also forms the non-rectifying electronic coupling with the original Retzius cell and rectifying junctions with the L motor neuron of the host ganglion. In addition it receives chemical inputs of the impulse from T and N sensory neurons of ganglion. Impulses in the implanted Retzius cell evoke synaptic potentials in the L motor neuron. In this paper the appearance of novel synapses, which are formed by implanting an extra mature neuron as a pre- or post-synaptic element, is described. It might represent functional development of central nervous system at an earlier stage.

Animals↗
PubMed1988

Differences in the kinetics of ionic currents in the somatic membrane of identified T- and N-mechanosensory neurons of medical leech.

The ionic currents in the membrane of the body of single T- and N-mechanosensory neurons were studied. Transient inward NA+-current followed by outward K+-current was recorded in the T-cells. The current was activated at membrane potential of -40 mV, reaching its maximum at -10 mV for 2 ms, whereby the reversal potential was about 25 mV. This current was inhibited by tetrodotoxin (TTX, 3 X 10(-6) M) and was eliminated in a Na+-free medium. In an Na+-free medium no inward current was registered upon increasing the Ca2+-concentration and after substituting Ca2+ with 10 mM Ba2+. In the N-cells the inward current was activated at membrane potential of -20 mV, reaching its maximum at -5 mV for 3-4 ms, while the reversal potential was about 45 mV. A time- and potential-dependent residual inward current was observed after application of TTX (3 X 10(-6) M) or in a Na+-free medium. This current increases upon rising the concentration of Ca2+ or when Ca2+ was replaced by 10 mM Ba2+. This current was blocked by methoxyverapamil (D-600, 5 X 10(-5) M). The results obtained manifest differences in the kinetics of the Na+-channels in the T- and N-neurons. In the membranes of the T-cells the Ca2+-channels are either poorly represented or totally lacking. Ca2+-conductivity was established in the N-cells and probably in their membranes exist Ca2+-channels which participate in their excitatory processes.

Action Potentials↗
PubMed1989

Peripheral target choice by homologous neurons during embryogenesis of the medicinal leech. II. Innervation of ectopic reproductive tissue by nonreproductive Retzius cells.

Most Retzius (Rz) cells innervate the body wall of their own and adjacent segments, whereas Rz cells in segments 5 and 6 [Rz (5,6)] innervate the reproductive tissue, which is found only in those segments. Results from the preceding paper (Loer and Kristan, 1989a) showed that Rz (5,6) and standard Rz cells do not normally compete for their respective peripheral targets. These experiments did not, however, distinguish between 2 other possible mechanisms of target selection: intrinsic differences in target preference or differences in the timing of target contact. In order to separate these possibilities experimentally, we transplanted reproductive primordia to standard segments. We found that standard Rz cells were capable of densely innervating ectopic reproductive tissue, provided the target was transplanted at an appropriate time and location. Furthermore, after some processes of standard Rz cells contacted ectopic reproductive tissue, the rest of the cell's processes showed their growth in a way reminiscent of Rz (5,6) processes. These results strongly suggest that Rz (5,6) innervate reproductive tissue at least partly because their processes contact this target during a period that is optimal for them to associate with the target, or when the reproductive tissue is most attractive to Rz processes, or both.

Animals↗