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PubMed1979

In vitro recalcification of the demineralized shell-repair membrane of the snail, Helix pomatia L.

The role of the amoebocytes in the calcification process of the shell-repair membrane of the snail, Helix pomatia, was investigated in vitro. The shell-repair membranes were demineralized with 0.5 M EDTA at pH 7.4. For the recalcification of the demineralized membranes two substrates were chosen: (i) Tris-buffered Helix pomatia-saline, pH 7.4, and (ii) Helix pomatia-saline supplemented with 5 mM CaCl2 and 5mM NaHCO3. The membranes were incubated in 2 ml substrate at 37 degrees C and examined after 2 h, 24 h, and 3, 5 and 7 days. Calcium deposition and crystal formation were observed within the membranes incubated in the salt-supplemented substrate. The control membranes were either heat-inactivated or deprived of lipids. No calcium precipitation was observed in control membranes. The experiments show that the recalcification of the shell-repair membrane is under strict cellular control and that the granules released from the amoebocytes serve as sites for calcium deposition. The role of phospholipids in the calcification process is discussed.

Animals↗

PubMed2005

Pro-oxidant effects of extremely low frequency electromagnetic fields in the land snail Helix aspersa.

Pro-oxidant effects of extremely low frequency (ELF) 50-Hz magnetic fields were investigated in the land snail Helix aspersa exposed both in short-term laboratory treatments and under field conditions by maintaining the organisms in the proximity of a power line for up to 2 months. Oxidative perturbations were investigated as individual antioxidants (catalase, glutathione reductase, glutathione S-transferases, and total glutathione) and total scavenging capacity toward peroxyl radicals and hydroxyl radicals. Accumulation of lipid peroxidation products, destabilization of lysosomal membranes, and loss of DNA integrity were also evaluated as markers of cell damage. The overall results indicated an oxidative challenge caused by ELF magnetic fields with particularly prompt and sensitive responses for catalase, glutathione reductase, and the overall capability to neutralize peroxyl radicals. Cell injuries occurred to different extents according to duration and intensity of electromagnetic exposure and confirmed complex cause-effect relationships between pro-oxidant factors, efficiency of antioxidant defenses, and the onset of oxidative toxicity. This study highlights the importance of a multimarker approach for detecting a wide panel of biological responses, the necessity of investigating the long-term effects of early oxidative responses, and the role of ELF in enhancing susceptibility to other forms of pathologies or diseases.

Animals↗

PubMed1996

Mathematical model of pacemaker activity in bursting neurons of snail, Helix pomatia.

On the basis of experimental data we have developed a mathematical model of pacemaker activity in bursting neurons of snail Helix pomatia which includes a minimal model of membrane potential oscillation, spike-generating mechanism, voltage- and time-dependent inward calcium current, intracellular calcium ions, [Ca2+]in, their fast buffering and accumulation, stationary voltage-dependent [Ca2+]in-inhibited calcium current. A resulting model of bursting pacemaker activity reproduces all experimental phenomena which were mimicked on the minimal model for membrane potential oscillation including (a) the effect of polarizing current on bursting activity, (b) an increase of input resistance during depolarizing phase, (c) induced hyperpolarization, etc. This model demonstrates adaptation of bursting activity to both the polarizing current and changes in the stationary sodium or potassium conductances. The model also reproduces the behavior of the transmembrane ionic current at membrane potentials clamped in different phases of slow-wave development; the calculated current-voltage relationships of the model neuronal membrane using a slow ramp potential clamp demonstrate hysteresis properties. Relationships between the model of bursting activity and the properties if intact bursting neurons are discussed.

Action Potentials↗

PubMed1988

Visualization of non-synaptic release sites in the myenteric plexus of the snail Helix pomatia.

Following conventional glutaraldehyde-osmium tetroxide fixation, a rich myenteric plexus was detected in the gastrointestinal tract of the snail Helix pomatia. Although hundreds of nerve processes were observed in the extensive myoneural neuropil, true synaptic specializations were not recognized in them. In the absence of synaptic specializations, tannic acid-Ringer incubation was applied to visualize the non-synaptic release sites in the enteric nerve plexus. After incubation for 1 h, a great number of exocytosis profiles were recorded at nerve-muscle contacts, at axoglial connections and in the myoneural neuropil. The frequency of occurrence of exocytosis profiles was the same for adrenergic and peptidergic fibres. In some gut wall areas, a dense staining of both basal lamina and collagen fibres was observed. Invagination of dense basal lamina into the omega-shaped profiles of the axolemma led to "false exocytosis" profiles. A detailed morphological analysis is needed to distinguish false exocytosis profiles from the true transmitter-releasing loci.

Animals↗

PubMed1976

Ultrastructural study of the shell-repair membrane in the snail, Helix pomatia L..

The shell-repair membrane of the snail, Helix pomatia, has been studied with the transmission electron microscope (TEM). The ultrastructure of the repair membrane, in the initial stages of calcification, revealed the presence of a fibrillar protein, proteoglycan granules, osmiophilic vesicles, and cytoplasmic dense bodies of different size and structure. The involvement of the cell constituents in the formation of calcifying centra and initial crystal formation is discussed. The amoebocytes present within the repair membrane appeared to be involved in three different functions: (1) phagocytosis, (2) release of granules, vesicles and dense bodies, and (3) secretin of a fibrillar protein. The possible lytic function of the amoebocytes is mentioned. The common features in the minearlizing process of the shell-repair membrane of the snail and the epiphyseal cartilage of the mammals were noted.

Animals↗

PubMed1984

The axosomatic contacts on the bursting neuron of the snail Helix pomatia. I. Ultrastructural features of the axosomatic contacts.

The analysis of serial ultrathin sections of the RPAI bursting neuron of the snail Helix pomatia reveals the presence of axosomatic contacts on its surface membrane. These contacts have a number of specific features: the presynaptic axon contains synaptic vesicles and electron-dense granules, typical of peptidergic terminals; the terminal part of the axon forms many finger-like processes which invaginate the neuronal soma; the width of the cleft (80 nm) in the area of the contact is larger than that in usual synaptic contacts; and there is a system of lacoons in the region of the axosomatic contact; this system is formed by protrusions of the soma and it accompanies the contact along its extent. It is suggested that the system of lacoons which communicates with the space between the terminal and the soma may serve as a ramified synaptic cleft into which the secretion from the terminal is released. This system may contribute to a considerable prolongation of the time of action of the secretory product on the membrane of the RPAI neuron.

Action Potentials↗

PubMed1985

Actions of the molluscan neuropeptide FMRF-amide on neurones in the suboesophageal ganglia of the snail Helix aspersa.

The effects of the molluscan neuropeptide FMRF-amide were tested on several neurones in the suboesophageal ganglia of the snail Helix aspersa. Almost all neurones tested responded to the peptide, some being hyperpolarized (H response) and others depolarized (D response). The H response is due primarily to an inward potassium current and may be blocked in 20 microM 4-aminopyridine. The hyperpolarizing actions of FMRF-amide and dopamine may be separated by ergometrine which blocks the response to dopamine but not to FMRF-amide. The D response is due mainly to an inward sodium current but this is not blocked by d-tubocurarine, morphine or TTX. It appears to be mediated by a distinct receptor/ionophore as excitation by ACh and 5-HT are both antagonized by d-tubocurarine. The Leu2-substituted analogue FLRF-amide was found to produce similar H responses to FMRF-amide, but was much less potent at producing D responses. It did, however, produce cross-desensitization of the D response to FMRF-amide, suggesting that it does bind to the FMRF-amide receptor.

Animals↗

PubMed2006

Electrical properties and cell-to-cell communication of the salivary gland cells of the snail, Helix pomatia.

The aim of the present study was to assess the cellular mechanism of secretion in the salivary gland of the snail, Helix pomatia, using electrophysiological, electron microscopic and immunohistochemical techniques. A homogeneously distributed membrane potential (-56.6 +/- 9.8 mV) was determined mainly by a K+ -electrochemical gradient and partly by the contribution of the electrogenic Na+ -pump and Cl- conductance. Low resistance electrical coupling sites were identified physiologically. Transmission electron microscopy and innexin 2 antibody revealed the presence of gap-junction-like membrane structures between gland cells. It is suggested that gap-junctions are sites of electrotonic intercellular communication, which integrate the gland cells into a synchronized functional unit in the acinus. Stimulation of the salivary nerve elicited secretory potentials (depolarization) which could be mimicked by local application of acetylcholine, dopamine or serotonin. In voltage-clamp experiments four major conductances were identified: a delayed rectifier (IK), a transient (IA) and a Ca2+ -activated outward K+ current (IK(Ca)) and Ca2+ -inward currents (ICa). It is suggested that one or more of these conductances may give rise to a stimulus activated secretory potential leading to excitation-secretion coupling and subsequent the release of the mucus from the gland cells.

Acetylcholine↗

PubMedDate not supplied

Excitatory and inhibitory monosynaptic peptidergic transmissions in the Cns of the snail Helix pomatia.

The results of an investigation of the properties of excitatory and inhibitory monosynaptic peptidergic transmission between identified nerve cells of the snail Helix pomatia are presented in this paper. It was demonstrated that stimulation of the presynaptic interneuron activates stationary and potential-and time-dependent ionic channels in the postsynaptic cells.

Animals↗

PubMed1986

The binding of acidic amino acids to snail, Helix aspersa, periesophagic ring membranes reveals a single high-affinity glutamate/kainate site.

The characterization of specific acidic amino acid binding sites to snail, Helix aspersa, ganglia membranes has been assayed using tritiated glutamate (L-[3H]Glu), aspartate (L-[3H]Asp), cysteine sulfinate (L-[3H]CSA) and kainate. At 2 degrees C, only L-[3H]Glu and [3H]kainate specific binding could be measured using a filtration procedure to separate bound from free ligand. The analysis of L-[3H]Glu specific binding reveals the presence of one class of high-affinity binding sites with Kd = 0.12 microM and Bmax = 30 pmol/mg protein. This L-[3H]Glu binding was specific, reversible and saturable. The order of potency of different substances, agonists or antagonists of the rat brain excitatory amino acid receptors, has been determined. Kainate was the best displacing agent, followed by ibotenate = L-Glu greater than L-alpha-aminoadipate (L-alpha-AA) greater than homocysteate (HCA). Using 10 nM [3H]kainate, a single class of binding site was detected. Its pharmacological properties indicate that it is likely identical to the L-[3H]Glu binding site. This L-Glu-kainate site possesses most of the properties expected for a specific receptor. However, whereas L-[3H]Glu binding could be detected on purified neuronal membranes, the major component of specifically bound L-[3H]Glu appeared to be located on the sheaths surrounding neuronal cell bodies. These findings suggest that Glu or another endogenous acidic amino acid may function as a transmitter at neuromuscular junctions in Helix periesophagic ring, acting at a receptor distinct from those on nerve cells.

Amino Acids↗

PubMed1992

Responses of the rectum and oesophagus of the snail Helix aspersa to purine nucleotides and nucleosides.

1. Purine compounds were examined for pharmacological activity in the rectum and oesophagus of the garden snail Helix aspersa. 2. In the rectum, adenosine, AMP, ADP and ATP (above 10 microM) and acetylcholine (above 1 nM) consistently caused concentration-dependent contractions. The slope of the dose-response curve for ADP in the rectum was significantly steeper than for the other purine compounds. The contractile responses to the nucleotides and acetylcholine, but not adenosine, were selectively potentiated by physostigmine (1 microM). Atropine (1 microM) and tubocurarine (30 microM) failed to block the responses to the purines or acetylcholine. 3. In the oesophagus, adenosine, AMP, ADP and ATP (above 10 microM) and acetylcholine (above 1 nM) caused concentration-dependent contractions that were antagonised by atropine (1 microM). Tubocurarine (30 microM) failed to block the responses to the purine compounds or acetylcholine. Physostigmine (1 microM) potentiated the responses to ADP and acetylcholine but not ATP, AMP or adenosine. 4. In both the rectum and the oesophagus, the synthetic analogues of purine compounds including 2-chloroadenosine, alpha,beta-methylene ATP and 2-methylthio ATP were inactive up to a concentration of 100 microM. 5. Electrical field stimulation of the rectum and oesophagus produced consistent contractions which were unaffected by atropine (1 microM), tubocurarine (30 microM) or physostigmine (1 microM). These responses were not modulated by any of the purine compounds or their stable analogues. 6. The responses obtained appear novel even within known invertebrate purinergic systems, suggesting a differentiation of purinoceptor subtypes in this species.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗

PubMed1989

Reactions of the lectin anti-AHP from the edible snail Helix pomatia with N-acetyl-D-galactosamine of streptococci.

The lectin anti-AHP obtained from the albumen gland of the edible snail, Helix pomatia, was used for the routine identification of group C streptococci. Without any exception all 1,045 strains of group C streptococci (S.equisimilis, and S.zooepidemicus, and S.dysgalactiae) were agglutinated by the Helix lectin, but none of the 12,264 strains of group A, 1,346 strains of group G, 330 strains of group B as well as that of other streptococcal groups. The presence of type-specific T antigens of group A streptococci in group C streptococci does not influence the agglutinability of S.equisimilis (group C). A few but not all strains of S.milleri either carrying or not group G specific carbohydrate and S.sanguis with group H antigen were agglutinated by the Helix lectin Anti-AHP. This suggests that terminal N-acetyl-D-galactosamine of these bacteria reacted with the Helix lectin (Anti-AHP). Therefore the Helix lectin is very useful tool for identification of group C streptococcus as well as for immunological studies.

Acetylgalactosamine↗

PubMed1986

Transmembrane outward hydrogen current in intracellularly perfused neurones of the snail Helix pomatia.

The ionic nature and pharmacological properties of the outward current activated by membrane depolarization were studied on isolated neurones of the snail Helix pomatia, placed in Na+- and Ca2+-free extracellular solutions and intracellularly perfused with K+-free solution ("nonspecific outward current"). It was shown that the amplitude and reversal potential of this current (estimated from instantaneous current-voltage characteristics) are determined mainly by the transmembrane gradient for H+ ions. Lowering of pHi induced an increase in the current amplitude and a shift of the reversal potential to more negative values; the shift magnitude was comparable with that predicted for the hydrogen electrode. Raising pHi, as well as lowering pHo, induced a decrease in the current amplitude and a displacement of the current activation curve to more positive potentials. Addition of EGTA (8 mmol/l) to the intracellular perfusate did not affect the current amplitude. Extracellular 4-aminopyridine (10 mmol/l), verapamil (0.25 mmol/l) or Cd2+ (0.5 mmol/l) blocked the current. It is concluded that the current studied is carried mainly by H+ ions. In the same neurones the nature of the fast decay of the calcium inward current was also studied (in the presence of extracellular Ca2+ ions). This decay considerably slowed when pHi was raised or pHo was lowered, and it became less pronounced upon extracellular application of 4-aminopyridine or upon intracellular introduction of phenobarbital (4 mmol/l) and tolbutamide (3 mmol/l). It is suggested that the fast decay of the calcium inward current is due to activation of a Ca-sensitive component of the hydrogen current which depends on accumulation of Ca2+ ions. The possible physiological role of the transmembrane hydrogen currents is discussed.

4-Aminopyridine↗

PubMed1998

[The modulating action of serotonin on single calcium channels in the neurons of the snail Helix pomatia].

The influence of a neurotransmitter serotonin (5-hydroxytriptamine, 5-HT) on single Ca2+ channel activity was studied on unidentified neurons of the snail Helix pomatia. Our findings showed that 5-HT influences the channel molecule in indirect manner, as it appeared effective at its application by adding to the bath solution, that had no contact with the tested membrane fragment. This finding excludes the possibility of direct binding of 5-HT to the channel molecule and shows that the effect is really mediated through a cytoplasmic messenger, cAMP-dependent cascade of phosphorylation. Also our investigations shows, that only one type of Ca2+ channel with the unitary conductance of 5 pS was identified in this kind of neurons.

Animals↗

PubMed1966

Protoplast formation and yeast cell-wall structure. The action of the enzymes of the snail, Helix pomatia.

1. The digestive juice of the snail Helix pomatia was used in the study of the degradation of isolated cell-wall preparations from a strain of Saccharomyces carlsbergensis. 2. The crude enzyme system was fractionated by gel filtration and the activities of the more specific fractions thus obtained were examined. 3. Results are discussed with respect to (a) the nature of various factors that are essential for protoplast formation and cell-wall dissolution and (b) structures envisaged in yeast cell walls that are responsible for the observed variations in susceptibility to attack by snail juice.

Cell Wall↗

PubMed1989

Specific insulin binding sites in snail (Helix aspersa) ganglia.

1. Insulin binding sites were characterized and quantified in snail (Helix aspersa) ganglia by incubation of tissue sections with 125I-porcine insulin, autoradiography with [3H]Ultrofilm, image analysis coupled to computer-assisted microdensitometry, and comparison with 125I-standards. Cellular localization was performed in the same sections by emulsion autoradiography. 2. Specific insulin binding sites were demonstrated in discretely localized groups of neurons of the cerebral, pleural, parietal, visceral, and pedal ganglia and in nerves. Scatchard analysis performed with consecutive sections from single animals revealed a single class of high-affinity insulin binding sites (Kd, 0.13 +/- 0.01 nM; Bmax, 157 +/- 10 fmol/mg protein). 3. Our results suggest that insulin may play a role as a neurotransmitter or neuromodulator in snail ganglia.

Animals↗

PubMed2001

Immunohistochemical localization and electrophysiological action of nociceptin/orphanin-FQ in the snail (Helix aspersa) neurons.

We report the existence and anatomical distribution to nociceptin/orphanin-FQ (N/O FQ)-like immunoreactivity in neurons and fibers in the perioesophageal ganglia of the snail (Helix aspersa). Intracellular recordings from perioesophageal ganglion neurons showed that the application of 10 microM N/O FQ produced an excitatory action in 22% of the neurons studied and an inhibitory action in 33% of the neurons regardless of their origin (cerebral or parietal ganglion). Our result provides evidence that N/O FQ-like peptide is located in whole perioesophageal ganglia (mainly in the cerebral one), and that it may serve as a neuromodulator of the neuronal spike discharge. These data support the idea that the N/O FQ opioid system has an early phylogenetic origin and a functional continuity during the course of evolution.

Action Potentials↗

PubMed1983

Non-respiratory haemolymph proteins in the vineyard snail Helix pomatia. Changes after phagocytosis in vivo.

Haemolymph proteins from the vineyard snail Helix pomatia were studied by chromatographic and immune-electrophoretic techniques with the dual purpose of characterizing the normal composition of haemolymph and to look for possible opsonins. The oxygen-carrying proteins, alpha- and beta-haemocyanin, were by far the most abundant proteins, but at least three non-respiratory proteins could be demonstrated. We found consistent changes in the appearance of the immunoprecipitation pattern of these non-respiratory proteins after the injection of particulate foreign matter into the snail's circulation, and we suggest that they may be opsonins. We also found a haemagglutinin in haemolymph. It was present in very low concentration and was similar to, but not identical with the haemagglutinin which is present in the albumin gland.

Animals↗