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PubMed1980

Characterization of the presynaptic muscarinic receptor in synaptosomes of Torpedo electric organ by means of kinetic and equilibrium binding studies.

The ligand binding properties of presynaptic muscarinic receptors present in purified synaptosomal fraction isolated from the electric organ of Torpedo have been studied, using the specific tritiated antagonist N-methyl-4-piperidylbenzilate ([3H]-4NMPB). Direct and competition binding studies revealed that antagonists bind with high affinity to the presynaptic receptor, with saturability occurring at very low ligand concentration, in a stereospecific manner, and according to a simple mass action law. The kinetic results for [3H]4NMPB binding could best be fitted by a two-step sequential isomerization model. The affinities of both agonists and antagonists decreased as a function of increasing ionic strength. Analysis of agonist binding was performed according to the two-site model suggested by Birdsall and Hulme. Varying the buffer conditions resulted in changes both in the affinities of the agonist for the two agonist sites and in their relative proportions. For a given buffer composition the proportion of high and low affinity sites is constant, but agonists affinities decrease as a function of increase in ionic strength. The finding that at a given ionic strength the proportion of high and low affinity agonist sites can be manipulated suggests that agonist binding sites in Torpedo receptor may interconvert. The apparent dissociation constants measured in Torpedo physiological buffer for both agonists and antagonists are in the same range as the concentrations affecting synaptosomal ACh release. The affinity of agonists towards the presynaptic muscarinic Torpedo receptor was found to be higher than their affinity towards the postsynaptic muscarinic receptor, e.g. in cat and rabbit irides, mouse cortex, etc., and closely resembles the affinity in mouse medulla pons. The localization of pre- and postsynaptic muscarinic receptors in view of their different binding properties is discussed.

Acetylcholine↗
PubMed2003

Dynamic dissolved oxygen concentration control for enhancing the formation rate of torpedo-stage embryos in carrot somatic embryo culture.

In utilizing somatic embryogenesis for transplant production, torpedo-stage embryos are harvested. In order to enhance the formation rate of torpedo-stage embryos to total embryos of all developmental stages in the culture at the time of harvest, a dynamic dissolved oxygen concentration (DO) control algorithm is proposed. The algorithm is based on the difference in developmental response of somatic embryogenesis to DO level depending on developmental stages, and the culture period was divided into three phases of different DO levels. The timing of the phase change was determined based on the formation rate of the embryos in each developmental stage in the suspension assessed by noninvasive monitoring of the culture. The induction of carrot (Daucus carroa L.) somatic embryogenesis resulted in doubled formation rate of torpedo-stage embryos by dynamic DO control compared to the 20% oxygen gas aeration, and 1.4 times higher formation rate compared to 6% oxygen gas aeration, while the total number of embryos did not differ among DO treatments. Plant conversion rate of torpedo-stage embryos cultured by the dynamic DO control was 70%, and was approximately the same as that in the control cultures. The relations between variations of medium pH and somatic embryogenesis were also analyzed.

Journal Article↗
PubMed1979

Equilibrium binding of [3H]tubocurarine and [3H]acetylcholine by Torpedo postsynaptic membranes: stoichiometry and ligand interactions.

Studies are presented of the equilibrium binding of [3H]-d-tubocurarine (dTC) and [3H]acetylcholine (AcCh) to Torpedo postsynaptic membranes. The saturable binding of [3H]dTC is characterized by two affinities: Kd1 = 33 +/- 6 nM and Kd2 = 7.7 +/- 4.6 microM, with equal numbers of binding sites. Both components are completely inhibited by pretreatment with excess alpha-bungarotoxin or 100 microM nonradioactive dTC and competitively inhibited by carbamylcholine with a KI = 100 nM, but not affected by the local anesthetics dimethisoquin, proadifen, and meproadifen. The biphasic nature of [3H]dTC binding was unaltered in solutions of low ionic strength and by preparation of Torpedo membranes in the presence of N-ethylmaleimide, a treatment which yields dimeric AcCJ receptors. dTC competitively inhibits the binding of [3H]AcCH and decreases the fluorescence of 1-(5-dimethylaminonaphthalene-1-sulfonamido)ethane-2-trimethylammonium (Dns-Chol) in a manner quantitatively consistent with its directly measured binding properties. It decreases the initial rate of 3H-labeled Naja nigricollis alpha-toxin binding by 50% at 60 nM with an apparent Hill coefficient of 0.58. The stoichiometry of total dTC, AcCh, and alpha-neurotoxin binding sites in Torpedo membranes was determined by radiochemical techniques and by a novel fluorescence assay utilizing Dns-Chol as an indicator, yielding ratios of 0.9 +/- 0.1:0.9 +/- 0.2:1, respectively. The biphasic equilibrium binding function is not unique to dTC since other ligands inhibited [3h]acCh binding in a biphasic manner with apparent inhibition constants as follows: gallamine triethiodide (K11 = 2 microM, K12 = 1 mM); Me2dTC (K11 = 500 nM, K12 = 10 microM); decamethonium (K11 = 100 nM, K12 = 1.6 microM). Carbamylcholine, however, inhibited [3H]AcCh binding with a single KI = 100 nM. The observed competition between those ligands and [3H] AcCh cannot be completely accounted for by competitive interaction with two different affinities, and the deviations are discussed in terms of the positive cooperativity of the [3H] AcCh binding function itself. It is concluded that dTC binds only to the AcCh sites in Torpedo membranes and that those sites display two affinities for dTC but only one for AcCh.

Acetylcholine↗
PubMed1997

Expression of human-Torpedo hybrid acetylcholine receptor (AChR) for analysing the subunit specificity of antibodies in sera from patients with myasthenia gravis (MG).

The nicotinic AChR, a pentamer composed of alpha2betagamma(or epsilon)delta subunits, is the autoantigen in the human autoimmune disease MG. Anti-AChR antibodies in MG sera bind mainly to conformational epitopes, therefore determination of their specificities requires the use of intact AChR. Indirect antibody competition studies have suggested that most MG antibodies are inhibited from binding to AChR by MoAb to the main immunogenic region (MIR) on the alpha-subunits. More recently, based on the knowledge that MG antibodies show little detectable cross-reaction with Torpedo AChR, we have shown, using mouse-Torpedo hybrid AChR, that most MG antibodies that detectably cross-react with the mouse AChR bind to the alpha-subunit. To analyse the whole anti-AChR antibody repertoire in MG sera, we expressed on stably transfected fibroblasts a novel human alpha+ Torpedo betagammadelta AChR and compared the antibody titres against human, Torpedo, and the hybrid AChR. Direct information was provided for the subunit specificity of several MoAbs and sera from 50 MG patients. On average, at least 48% of the anti-AChR antibodies in the sera were directed against the alpha-subunit. Interestingly, the anti-alpha-subunit antibodies predominated in low titre (0.6-7.4 nM) but not in high titre (10-386 nM) sera, where they comprised on average 68% versus 23% of the antibodies, respectively. Finally, the directly determined anti-alpha-subunit antibodies and the anti-MIR antibodies defined by antibody competition were significantly correlated, thus suggesting that at least a significant fraction of the anti-MIR antibodies in MG sera bind to the alpha-subunit.

Animals↗
PubMed1972

Characterization and partial purification of the acetylcholine receptor from Torpedo electroplax.

Binding of acetylcholine in the concentration range 1 nM-1 muM was measured by equilibrium dialysis to a particulate preparation of Torpedo electroplax, without or with prior treatment of the tissue with one of three chemical modifying reagents. Significant reduction in binding of acetylcholine resulted after treatment with 1,4-dithiothreitol, p-chloromercuribenzoate, or p-(trimethylammonium)-benzenediazonium fluoroborate. Partial reversal of the reduction in binding occurred when dialysis was performed in the presence of 5,5'-dithiobis-(2-nitrobenzoic acid) or potassium ferricyanide (in the case of treatment with dithiothreitol), and 2-mercaptoethanol (in the case of treatment with p-chloromercuribenzoate). It is concluded that the functional acetylcholine-receptor macromolecule of Torpedo electroplax has disulfide bond(s), sulfhydryl group(s), and one or more of the amino acids vulnerable to diazotization by p-(trimethylammonium)-benzenediazonium fluoroborate. This, plus the effect of phospholipase C (EC 3.1.4.3) in elimination of detectable binding of acetylcholine after electrofocusing, is additional evidence that the functional acetylcholine receptor is a phospholipoprotein or a phospholipid-protein complex, which has a low isoelectric point of 4.5 +/- 0.2, yet is denatured by exposure to low pH for 24 hr. Due to this adverse effect, recovery of binding of acetylcholine after electrofocusing, as detected by equilibrium dialysis or ultrafiltration, is only 23% and, so far, only 6.3-fold purification of functional acetylcholine receptors by this technique is possible. Three or two forms of acetylcholinesterase (EC 3.1.1.7), whose peaks have isoelectric points ranging from 4.3 to 7.2, appear after electrofocusing of Torpedo extracted with 1% Triton X-100 or Lubrol, respectively. The major peak in either preparation has an isoelectric point of 5. Although the peaks of the functional acetylcholine receptors and of acetylcholinesterase of Torpedo electroplax are separable by electrofocusing, it has not been possible to isolate fractions that contain functional receptors but that are free of acetylcholinesterase. The opposite is possible.

Acetylcholine↗
PubMed1981

Alpha-bungarotoxin binding in house fly heads and Torpedo electroplax.

House fly heads contain a site that binds alpha-bungarotoxin with high affinity. It is present at about 23 pmol/g of heads and binds alpha-bungarotoxin (labeled with [3H]pyridoxamine phosphate) reversibly with a Kd of 6 nM. The effects of 48 drugs have been compared on the alpha-bungarotoxin binding sites of house fly and Torpedo. The pharmacology of the house fly sites is similar to that previously reported for neuronal alpha-bungarotoxin binding sites in both vertebrates and invertebrates and is distinguishable from that of the classic nicotinic neuromuscular acetylcholine receptor, as exemplified by that of Torpedo electroplax. Differences between the house fly site and Torpedo include higher affinities of the Torpedo receptor for decamethonium, hexamethonium, carbamylcholine, and acetyl-beta-methylcholine, but lower affinities for nicotine, atropine, and dihydro-beta-erythroidine.

Animals↗
PubMed1980

In situ labeling of Torpedo and rat muscle acetylcholine receptor by a photoaffinity derivative of alpha-bungarotoxin.

We synthesized a photoaffinity derivative of 125I-alpha-bungarotoxin that binds tightly and specifically to the acetylcholine receptor. We used this reagent to label the receptor in membranes from Torpedo electric organ and rat muscle and have analyzed the labeled polypeptides by immunoprecipitation and sodium dodecyl sulfate-gel electrophoresis. Reaction of the modified toxin with the Torpedo receptor in situ covalently labels the same four polypeptides as seen in Torpedo receptor preparations after solubilization and purification. The toxin derivative labels five polypeptides in muscle membranes that correspond in molecular weight to the subunits of the purified muscle receptor. These results provide evidence that, for both Torpedo and muscle receptors, the polypeptides associated with the purified protein also form part of the receptor in situ.

Affinity Labels↗
PubMed2001

An ultrastructural study of germ cells during ovarian differentiation in Torpedo marmorata.

An ultrastructural investigation, performed on embryos, neonates, subadult and adult females, demonstrated that in Torpedo marmorata oogenesis occurs very early in life and continues, in its proliferative phase, also after birth. Clusters of early meiotic cells were already evident in the ovarian cortex of 6-cm-long embryos, as well as in the ovary of newborns and three-month-old young. Conversely, in the ovaries of subadult and adult females, all the germ cells present were organized into follicles, and no clusters of oogonia and early meiotic cells were generally found in the cortex, except for one adult female where clusters of germ cells not organized in follicles were found in the cortex. These data demonstrated that, in Torpedo marmorata, oogenesis is immediate, and, as oogonia persist after birth, more similar to that of mouse, monkey, rabbit, and ferret (Mauleon Arch Anat Microsc, 1967; 56:125-150; Byskov and Hoyer 1994) than to that of human, rat, pig, and guinea pig (Byskov and Hoyer 1994). Such a pattern is in agreement with the reproductive strategy of Torpedo, a scantly prolific species with low uterine fecundity. The presence of meiotic cells that are not organized in follicles in one adult female might be consistent with the large individual variability characterizing cartilaginous fishes. The possibility that such a character is typical of mature females should be rejected as oogonia and early meiotic cells were not found inside the totally sectioned gonads of subadult and adult females.

Animals↗
PubMed1985

Torpedo electromotor system development: neuronal cell death and electric organ development in the fourth branchial arch.

The fourth branchial arch of Torpedo marmorata has been examined at the light and electron microscopic level during development. Of interest was the determination of the extent of electric organ tissue reported to be present in this arch and its possible relationship to electromotoneuron cell death in the electric lobes. The main electric organ of the torpedo is derived from the hyoid and first three branchial arches and is innervated by four major electromotor nerves. Extensive electromotoneuron cell death occurs in the electric lobes and most notably in the posterior poles. This feature could be due to a tendency for these neurons to innervate the fourth branchial arch where little or no electric tissue is formed. Our findings support this conclusion but are not entirely consistent with the idea that a population mismatch has occurred. This is because cell death precedes the genesis of the target cells. The presence of innervated differentiated electric tissue in this arch is also reported, leading to the conclusion that Torpedo marmorata possesses an accessory electric organ.

Animals↗
PubMed1987

cDNA sequences of Torpedo marmorata acetylcholinesterase: primary structure of the precursor of a catalytic subunit; existence of multiple 5'-untranslated regions.

cDNA clones coding for a catalytic subunit of acetylcholinesterase were isolated from cDNA libraries constructed from Torpedo marmorata electric organ. The nucleotide sequence of the cloned cDNAs codes for a 599-amino acid precursor containing a 24-amino acid signal peptide. This primary structure has been compared with the sequences of Torpedo californica and Drosophila melanogasta acetylcholinesterases, and with that of human butyrylcholinesterase. Genomic blot experiments carried out with cDNA restriction fragments used as hybridization probes are in agreement with the existence of a single gene coding for the different catalytic subunits of Torpedo acetylcholinesterase. Unexpectedly, we observed multiple 5'-untranslated regions, which may contain several initiation codons.

Acetylcholinesterase↗
PubMed1992

Binding of botulinum neurotoxin to pure cholinergic nerve terminals isolated from the electric organ of Torpedo.

Torpedo electric organ has been used to study the binding of botulinum neurotoxin type A to pure cholinergic synaptosomes and presynaptic plasma membrane. 125I-labeled botulinum neurotoxin type A exhibits specific binding to cholinergic fractions. Two binding sites have been determined according to data analysis: a high affinity binding site (synaptosomes: Kd = 0.11 +/- 0.03 nM, Bmax = 50 +/- 10 fmol.mg prot-1; presynaptic plasma membrane: Kd = 0.2 +/- 0.05 nM, Bmax = 150 +/- 15 fmol.mg prot-1) and a low affinity binding site (synaptosomes: Kd approximately 26 nM, Bmax approximately 7.5 pmol.mg prot-1; presynaptic plasma membrane: Kd approximately 30 nM, Bmax approximately 52 pmol.mg prot-1). The binding of 125I-botulinum neurotoxin type A is decreased by previous treatment of synaptosomes by neuraminidase and trypsin, and by a preincubation with bovine brain gangliosides or antiserum raised against Torpedo presynaptic plasma membrane. When presynaptic plasma membranes are blotted to nitrocellulose sheet, either 125I-botulinum neurotoxin or botulinum toxin-gold complexes bind to a M(r) approximately 140,000 protein. Botulinum toxin-gold complexes have also been used to study the toxin internalization process into Torpedo synaptosomes. The images fit the three step sequence model in the pathway of botulinum neurotoxin poisoning.

Acetylcholine↗
PubMed1993

The proportion of amphiphilic choline acetyltransferase in Drosophila melanogaster is higher than in rat or Torpedo and is developmentally regulated.

We show that in the central nervous system of the fly, Drosophila melanogaster, choline acetyltransferase (ChAT) activity exists under two molecular forms, a soluble, hydrophilic form and a membrane-bound, amphiphilic form. This is based on the following demonstrations of differential solubilization and interaction with non-denaturing detergents: sequential extraction of Drosophila heads produced low-salt-soluble (83-87%) and detergent-soluble (6-7%) ChAT activity. Sedimentation in sucrose gradients of detergent-soluble ChAT was found to be influenced by the type of detergent present in the gradient (Triton X-100 and Brij 96). This was not the case for low-salt-soluble ChAT. To further confirm these findings, we subjected Drosophila heads to Triton X-114 fractionation. This method, which yielded 12% of amphiphilic ChAT activity, separates hydrophilic from amphiphilic proteins. Compared to central nervous tissue of rat and Torpedo electric lobes, Drosophila head contained the highest proportion of amphiphilic ChAT activity. Synaptosomes isolated from Torpedo electric organ exhibited higher levels of amphiphilic ChAT than did electric lobes. Of the three animal species analyzed here, the Torpedo amphiphilic enzyme was the most hydrophobic and the rat enzyme the least hydrophobic. The proportion of amphiphilic ChAT was analyzed during Drosophila development. The percentage of this activity increased about 7 times from embryo to larva and then remained constant until the adult fly age.

Aging↗
PubMed1983

Differential inhibition of the release of endogenous and newly synthesized acetylcholine from Torpedo synaptosomes by presynaptic muscarinic receptors.

Activation of Torpedo presynaptic muscarinic acetylcholine (ACh) receptors with the agonist oxotremorine (20 microM) results in the inhibition of Ca2+-dependent release of endogenous ACh from Torpedo synaptosomes. This effect is reversed by the muscarinic antagonist atropine (1 microM) which, by itself, has no effect. In contrast, under the same conditions the amount of newly synthesized radiolabeled [3H]ACh released is not affected by muscarinic ligands. These findings suggest that presynaptic muscarinic inhibition in the Torpedo is due to interference with the mobilization of ACh from a storage pool.

Acetylcholine↗
PubMed1986

Identical N-terminal peptide sequences of asymmetric forms and of low-salt-soluble and detergent-soluble amphiphilic dimers of Torpedo acetylcholinesterase. Comparison with bovine acetylcholinesterase.

We have determined partial N-terminal sequences of acetylcholinesterase (AChE) catalytic subunits from Torpedo marmorata electric organs and from bovine caudate nucleus. We obtain identical sequences (23 amino acids) for the soluble ('low-salt-soluble' or LSS fraction) and particulate ('detergent-soluble', or DS fraction) amphiphilic dimers (G2 form) and for the asymmetric, collagen-tailed forms ('high-salt-soluble', or HSS fraction, A12 + A8 forms). There are two amino acid differences, at position 3 (Asp/His) and 20 (Ile/Val), with the sequences obtained for T. californica by MacPhee-Quigley et al. [(1985) J. Biol. Chem. 260, 12185-12189] for the soluble G2 form and the lytic G4 form which is derived from asymmetric AChE. The bovine sequence (12 amino acids) presents an identity of 4 amino acids (Glu-Leu-Leu-Val) with that of Torpedo, at positions 5-8 (Torpedo) and 7-10 (bovine). There is also a clear homology with the sequence of human butyrylcholinesterase [(1986) Lockridge et al. J. Biol. Chem., in press] indicating that these enzymes probably derive from a common ancestor.

Acetylcholinesterase↗
PubMed1988

Action of polychlorocycloalkane insecticides on binding of [35S]t-butylbicyclophosphorothionate to Torpedo electric organ membranes and stereospecificity of the binding site.

Binding of [35S]t-butylbicyclophosphorothionate ([35S]TBPS) to Torpedo electric organ membranes was characterized. A dose- and pH-dependent binding (100.8 pmol/mg protein) was detected with a single affinity (Kd of 0.9 microM) in the presence of 150 mM KCl at pH 6.8. Other anions such as Br- and I- also increased binding affinity, but to a lower degree than Cl-, which increased the affinity by two- to threefold. In presence of 150 mM KCl, [35S]TBPS binding was inhibited noncompetitively by Zn2+ and by 4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid (DIDS) (IC50 of 9 microM). The gamma-isomer of hexachlorocyclohexane (BHC) was much more potent in inhibiting this [35S]TBPS binding and the inhibition was competitive (Ki = 40 nM). Like binding of [35S]TBPS to the gamma-aminobutyric acid (GABA) receptor, its binding to Torpedo membranes was inhibited by pentobarbital, mephobarbital, and hexobarbital (IC50 of 85, 225, and 300 microM), respectively), but not by phenobarbital. Binding was not inhibited by diazepam, GABA, bicuculline, or avermectin B1a, ligands that bind to the GABAA receptor. [35S]TBPS binding was inhibited by BHC isomers with the following decreasing order of potency alpha = gamma greater than sigma greater than beta, and by cyclodiene insecticides. Endrin was more potent than dieldrin, but endosulfan I and II had similar effects. The data suggest that the binding site for polychlorocycloalkane insecticides on this protein is much less stereoselective than that of the Cl- channel of the GABAA receptor. Also, even though this Torpedo protein has higher affinity for insecticides, such as gamma-BHC, than does the GABAA receptor, it is the latter whose specificity correlates best with polychlorocycloalkane toxicity. Nevertheless, because of its high affinity for gamma-BHC such a protein in muscles or brain may be an important target for the action of this insecticide.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1992

Epitope mapping of monoclonal antibodies to Torpedo acetylcholine receptor gamma subunits, which specifically recognize the epsilon subunit of mammalian muscle acetylcholine receptor.

Epitopes for four monoclonal antibodies (mAbs) to the gamma subunit of Torpedo nicotinic acetylcholine receptor (AChR), and one mAb crossreactive with the gamma and delta subunits of Torpedo AChR were mapped using overlapping synthetic peptides corresponding to the complete amino acid sequence of Torpedo gamma subunit. The epitopes for all mAbs were within a 50 residue sequence region, on the cytoplasmic surface of the AChR. Three mAbs crossreacted with mammalian muscle AChRs. Two of them specifically recognized the epsilon subunit of AChRs at adult neuromuscular junction. The epsilon-specific mAbs were used, in conjunction with mAbs specific for the alpha and beta subunits and anti-peptide antisera specific for the epsilon, gamma and delta subunits, to identify in Western blots the subunit complement of embryonic and adult bovine muscle AChRs.

Amino Acid Sequence↗
PubMed1984

Immunisation with Torpedo acetylcholine receptor.

Acetylcholine mediates the transfer of information between neurons in the electric organ of, for example, Torpedo as well as in vertebrate skeletal muscle. The nicotinic acetylcholine receptor complex translates the binding of acetylcholine into ion permeability changes. This leads to an action potential in the muscle fibre. The nicotinic acetylcholine receptor protein has been purified from Torpedo by use of affinity chromatography. The receptor is an intrinsic membrane glycoprotein composed of five polypeptide chains. When various animals are immunised with the receptor they demonstrate clinical signs of severe muscle weakness coincident with high antibody titres in their sera. The symptoms resemble those found in the autoimmune neuromuscular disease myasthenia gravis in humans. This animal model has constituted a unique model for studying autoimmune diseases. This paper reviews some of the work using Torpedo acetylcholine receptor in order to increase the understanding of the motor nervous system function and myasthenia gravis. It is now known that the nicotinic acetylcholine receptor protein is the antigen involved in myasthenia gravis. The mechanism of immune damage involves a direct block of the receptor function. This depends on the presence of antibodies which crosslink the postsynaptic receptors leading to their degradation. The questions to be answered in the future are; (a) what initiates or triggers the autoimmune response, (b) how do the antibodies cause the symptoms--is there a steric hindrance of the interaction of acetylcholine and the receptor, (c) why is there not a strict relationship between antibody titre and severity of symptoms, and (d) why are some muscles affected and other spared? With help of the experimental model, answers to these questions may result in improved strategies for the treatment of the autoimmune disease myasthenia gravis.

Adjuvants, Immunologic↗
PubMed1991

Effect of opioid peptides on electrically evoked acetylcholine release from Torpedo electromotor neurons.

The opioid peptide dynorphin A(1-8) (1 micron) increased acetylcholine release from the Torpedo electric organ by approximately twofold. This effect was reversed by the opiate antagonist naloxone. The effect of Dyn A(1-8) on acetylcholine release was found to vary in magnitude with the seasons of the year, with maximal enhancement being observed in the summer and none in winter. Dynorphin B, methionine-enkephalin and leucine-enkephalin also increased acetylcholine release and showed similar seasonal variations. These findings suggest that acetylcholine release from Torpedo electromotor neurons is regulated by opiate receptors. The physiological significance of these observations is discussed in view of the previous findings that the Torpedo neurons contain an endogenous enkephalin-like peptide.

Acclimatization↗