PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Torpedo”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed1990

Temperature-sensitive expression of all-Torpedo and Torpedo-rat hybrid AChR in mammalian muscle cells.

When the four subunits of the Torpedo californica nicotinic acetylcholine receptor (AChR) are expressed in mammalian fibroblasts, they properly assembly into alpha 2 beta gamma delta pentamers only at temperatures lower than 37 degrees C (Claudio, T., W. N. Green, D. S. Hartman, D. Hayden, H. L. Paulson, F. J. Sigworth, S. M. Sine, and A. Swedlund. 1987. Science (Wash. DC). 238:1688-1694). Experiments here with rat L6 myoblast cell lines indicate that this temperature sensitivity is not specific to fibroblasts, but is intrinsic to Torpedo subunits. A clonal isolate of L6 cells cotransfected with the four Torpedo subunit cDNAs synthesizes the exogenous AChR subunits at 37 degrees and 26 degrees C, but expresses Torpedo AChR complexes only at the lower temperature. When Torpedo alpha alone is expressed in L6 myotubes, hybrid AChRs are formed, again only at temperatures below 37 degrees C. These hybrid AChRs can contain either two Torpedo alpha subunits or one each of rat and Torpedo alpha, proving that the two alpha subunits in an AChR pentamer need not derive from the same polysome. Further analysis of hybrid and all-Torpedo AChR established that there is no internally sequestered pool of AChR at the nonpermissive temperature, and that the AChR, once formed, is thermostable. Two lines of experimentation with alpha subunits expressed in fibroblasts indicate that alpha polypeptides exhibit different conformations at 26 degrees and 37 degrees C, favoring the hypothesis that the temperature-sensitive step occurs before assembly and reflects, at least in part, misfolding of subunits: at 37 degrees C, there is a reduction in the fraction of alpha subunits that (a) bind the AChR antagonist alpha-bungarotoxin with high affinity; and (b) bind a monoclonal antibody that recognizes correctly folded and/or assembled alpha subunit.

Animals↗
PubMed1992

Crosslinking of proteins in acetylcholine receptor-rich membranes from Torpedo californica: relation of 43-kD protein and Torpedo dystrophin to acetylcholine receptor.

We examined the spatial relation of 43-kD protein and Torpedo dystrophin, which are cytoplasmic peripheral membrane proteins in the nicotinic acetylcholine receptor (AChR)-rich membranes, to AChR. We used three kinds of the heterobifunctional crosslinking reagents to crosslink proteins in the AChR-rich membranes. Products crosslinked by SMPB (14.5 A span) including 43-kD protein and Torpedo dystrophin appeared at the tops of the stacking gels at the concentrations of 8.89 x 10(-5)M to 8.89 x 10(-3)M SMPB. High molecular weight materials (crosslinked products) increased with increasing concentrations of the crosslinker. On the other hand, band intensity of alpha, beta, and delta subunits of AChR remained unchanged up to a concentration of 2.67 x 10(-3)M SMPB, while the band of gamma subunit diminished at the same concentrations as did that of the 43-kD protein. Torpedo dystrophin was also crosslinked at the same concentrations as were effective for the 43-kD protein and gamma subunit. On the basis of these results, we conclude that the 43-kD protein is intimately associated with the gamma subunit of AChR and Torpedo dystrophin.

Animals↗
PubMed1986

Torpedo electromotor system development: biochemical differentiation of Torpedo electrocytes in vitro.

The accumulation of 2 postsynaptic proteins--the acetylcholine receptor and acetylcholinesterase, total protein and lactate dehydrogenase levels, and the evolution of the multiple molecular forms of acetylcholinesterase (exhibiting apparent sedimentation coefficients of 17, 13, 11 and 6S) have been examined in aneural cultures of embryonic Torpedo electric organ explanted before, during or after electrocyte differentiation and the onset of synaptogenesis. During electrocyte differentiation in vitro, with explants taken before the 38 mm stage, the relative proportions of the 17, 13 and 11S forms change in vitro as in vivo but the 6S form remains abnormally dominant. In tissue explants taken from 38 to 47 mm stage embryos, the 4 major molecular forms of acetylcholinesterase differentiate in a manner identical to that observed in vivo. In explants taken after the onset of synaptogenesis (55-80 mm stages), the proportions of the acetylcholinesterase forms change as in vivo only during the first week in vitro whilst accumulation is occurring at the normal in vivo rate. The switch to the high acetylcholine receptor and acetylcholinesterase accumulation rate that occurs when synaptogenesis begins in vivo is not observed after any time lag in vitro with tissue explanted before the stage (55 mm) at which synaptogenesis begins. The effects on acetylcholinesterase and acetylcholine receptor accumulation of supplementing the medium with a neural tissue extract are described. The experiments were designed to elucidate the factors and mechanisms that regulate the differentiation and formation of chemical synapses using the electric organ of Torpedo marmorata as a model system. The results demonstrate that the complex changes occurring in the multiple molecular forms of acetylcholinesterase during electrocyte differentiation are not under direct neural control but that the switch to an increased acetylcholinesterase and acetylcholine receptor accumulation rate may be triggered by an external, possible neural factor.

Acetylcholinesterase↗
PubMed1987

Synapsin I is associated with cholinergic nerve terminals in the electric organs of Torpedo, Electrophorus, and Malapterurus and copurifies with Torpedo synaptic vesicles.

Using an affinity-purified monospecific polyclonal antibody against bovine brain synapsin I, the distribution of antigenically related proteins was investigated in the electric organs of the three strongly electric fish Torpedo marmorata, Electrophorus electricus, Malapterurus electricus and in the rat diaphragm. On application of indirect fluorescein isothiocyanate-immunofluorescence and using alpha-bungarotoxin for identification of synaptic sites, intense and very selective staining of nerve terminals was found in all of these tissues. Immunotransfer blots of tissue homogenates revealed specific bands whose molecular weights are similar to those of synapsin Ia and synapsin Ib. Moreover, synapsin I-like proteins are still attached to the synaptic vesicles that were isolated in isotonic glycine solution from Torpedo electric organ by density gradient centrifugation and chromatography on Sephacryl-1000. Our results suggest that synapsin I-like proteins are also associated with cholinergic synaptic vesicles of electric organs and that the electric organ may be an ideal source for studying further the functional and molecular properties of synapsin.

Animals↗
PubMed1989

Effects of intratesticular injections of estradiol and gonadotropin-releasing hormone (GnRHA, HOE 766) on plasma androgen levels in intact and hypophysectomized Torpedo marmorata and Torpedo ocellata.

The effect of a gonadotropin-releasing hormone analog (GnRHA, HOE766) was studied in hypophysectomized elasmobranch fish Torpedo marmorata and T. ocellata. In addition, estradiol (E2) effects were studied in intact and hypophysectomized (HPX) animals. Plasma androgen concentrations were measured 2 or 6 hr after GnRHA (100 ng or 10 micrograms) or 6 hr after E2 (10(-9) or 10(-6) M) intratesticular injections. Both GnRHA and E2 induced the increase of plasma androgen levels in HPX fish. E2 also enhanced androgen levels in intact animals. It is concluded that GnRH-like substances and E2 may modulate testicular activity in elasmobranch fish.

Androgens↗
PubMed1992

Modulation of nicotinic acetylcholine receptor channel by pH: a difference in pH sensitivity of Torpedo and mouse receptors expressed in Xenopus oocytes.

1. In this study, effects of pH on the ion channel function of nicotinic acetylcholine receptor (nAChR) from Torpedo californica electroplax and mouse muscle BC3H-1 cells were investigated using Xenopus laevis oocytes injected with in vitro synthesized RNA transcripts. The acetylcholine (ACh)-induced whole-cell peak current responses and slow desensitization rates were measured by voltage-clamp. 2. The ACh-induced peak currents of Torpedo nAChRs were reversibly diminished when extracellular pH was reduced from 7.4 to 5.0 and increased at pH greater than 7.4. This pH dependence had an apparent pKa of 7.0. In contrast, the peak current of mouse muscle nAChRs were reversibly decreased at both acidic and alkaline pH's. This bell-shaped pH profile with a maximum at pH 7.4 had two apparent pKa values of 5.6 and 9.2. 3. The peak current responses of four mouse-Torpedo nAChR hybrids consisting of three Torpedo subunits and one mouse nAChR subunit displayed similar pH profiles at acidic pH, with a pKa of 6.0 to 6.5, which lay between the pKa 5.6 for mouse and the pKa 7.0 for Torpedo nAChRs. Two of these combinations, alpha M beta T gamma T delta T and alpha T beta T gamma M delta T, also had an alkaline pH dependence of the current response similar to that of mouse receptor, with a pKa of 9.3 to 9.5. 4. The slow desensitization rate of Torpedo nAChRs increased at both acidic and alkaline pH's, with two pKa values of 6.5 and 9.5, whereas that of mouse muscle receptors remained unchanged from pH 6.5 to pH 9.0 and increased at pH less than 6.0, with a pKa of 4.7. 5. Substitution of each subunit of Torpedo nAChR with a mouse counterpart resulted in a pH dependence pattern (pKa 6.0 to 6.4 and pKa 9.1 to 9.3) similar to that of Torpedo nAChR except the substitution with mouse beta subunit (pKa 4.8 and pKa 8.9), which appears to carry the characteristic acidic group determining the pH dependence of mouse nAChR desensitization. 6. The apparent pKa values obtained from the pH dependence studies of nAChR channel activation and desensitization suggest the involvement of different amino acid residues in determining channel functions of Torpedo and mouse nAChRs. The groups with pKa 7.0 and 6.5 on Torpedo nAChR can be tentatively identified as His residues, whereas those with pKa 5.6 and 4.7 on mouse receptor as Glu or Asp residues. The alkaline pKa of 8.9 to 9.5 may be Cys, Tyr, or Lys.

Allosteric Regulation↗
PubMed1979

Immunochemical similarities between subunits of acetylcholine receptors from Torpedo, Electrophorus, and mammalian muscle.

Polypeptide chains composing acetylcholine receptors from the electric organs of Torpedo californica and Electrophorus electricus were purified and labeled with 125I. Immunochemical studies with these labeled chains showed that receptor from Electrophorus is composed of three chains corresponding to the alpha, beta, and gamma chains of receptor from Torpedo but lacks a chain corresponding to the delta chain of Torpedo. Experiments suggest that receptor from mammalian muscle contains four groups of antigenic determinants corresponding to all four of the Torpedo chains. Binding of 125I-labeled chains was measured by quantitative immune precipitation and electrophoresis. Antisera to the following immunogens were used: denatured alpha, beta, gamma, and delta chains of Torpedo receptor, native receptor from Torpedo and Electrophorus electric organs and from rat and fetal calf muscle, and human muscle receptor (from autoantisera of patients with myasthenia gravis). The four chains of Torpedo receptor were immunologically distinct from one another and from higher molecular weight chains found in electric organ membranes. Antibodies to these chains reacted very efficiently with native Torpedo receptor, but the reverse was not true. Antibodies to native receptor from Torpedo and Electrophorus reacted slightly with each of the chains of the corresponding receptor. However, cross-reaction between chains and antibodies to any native receptor was most obviuos with the alpha chain of Torpedo or the corresponding alpha' chain of Electrophorus. Antiserum to alpha chains exhibited higher titer aginst receptor from denervated rat muscle. Antibodies from myasthenia gravis patients did not cross-react detectably with 125I-labeled chains from electric organ receptors. Most interspecies cross-reaction occurred at conformationally dependent determinants whose subunit localization could not be determined by reaction with the denatured chains.

Animals↗
PubMed1992

The torpedo (DER) receptor tyrosine kinase is required at multiple times during Drosophila embryogenesis.

The torpedo (DER) gene of Drosophila, which encodes a receptor tyrosine kinase of the EGF receptor subfamily, is essential for oogenesis, embryogenesis and imaginal disc development. To gain insight into the nature of the signals transduced by the torpedo product, we have characterized the gene's loss-of-function phenotype in the embryo. Through the induction of germline clones, we provide a genetic demonstration that maternal torpedo product does not contribute to zygotic development. Thus, the embryonic lethal phenotypes examined accurately reflect the consequences of eliminating all gene activity from the zygote. Temperature-shift experiments with the conditional allele topIF26 show that torpedo is required at two distinct times during embryonic development: the gene is first needed for germband retraction and for the production of anterior, posterior and ventral cuticle, then later for the secretion of ventral denticles. Since denticle formation can be severely disrupted in topIF26 animals without affecting cuticle production, the early and late requirements for torpedo appear to be functionally unrelated. torpedo, therefore, is required at multiple times in the development of the ventral epidermis, and may transduce qualitatively different signals. Since the early requirement for torpedo correlates with the first visible defect in embryonic development, increased cell death in the amnioserosa, cephalic ectoderm and ventral epidermis, the abnormalities in cuticle production and germband shortening seen in the mutant may be secondary consequences of a primary defect in cell viability. Given that the onset of cell death in torpedo embryos is not preceded by any obvious defects in mitogenesis, the establishment of cell identities or the maintenance of gene expression, it is possible that torpedo transduces a signal necessary for cell survival per se during early embryogenesis. During late embryogenesis, torpedo may mediate the reception of a second signal which regulates ventral epidermal cell differentiation.

Animals↗
PubMed1989

Change in desensitization of cat muscle acetylcholine receptor caused by coexpression of Torpedo acetylcholine receptor subunits in Xenopus oocytes.

Cat muscle acetylcholine receptors (AcChoR) expressed in Xenopus oocytes desensitized more slowly than Torpedo electric organ AcChoRs, also expressed in oocytes. To examine the bases for the different degrees of desensitization, cat-Torpedo AcChoR hybrids were formed by injecting oocytes with cat denervated muscle mRNA mixed with a large excess of cloned Torpedo AcChoR subunit mRNAs. Hybrid AcChoRs formed by coinjection of cat muscle mRNA with the Torpedo beta or delta subunit mRNAs desensitized as slowly as cat AcChoR. In contrast, the hybrid AcChoRs expressed by coinjection with the Torpedo gamma subunit mRNA desensitized much more rapidly than cat AcChoR. The AcChoRs expressed in oocytes injected with cat muscle mRNA together with the Torpedo beta, gamma, and delta subunit mRNAs desensitized as rapidly as Torpedo AcChoR, indicating that the cat alpha subunit does not play an important role in determining the slow rate of desensitization. It is concluded that the difference in the rates of desensitization of cat and Torpedo AcChoRs is determined mainly by differences in their respective gamma subunits.

Animals↗
PubMed1978

Binding of antibodies to acetylcholine receptors in Electrophorus and Torpedo electroplax membranes.

Antisera against purified acetylcholine receptors from the electric tissues of Torpedo californica and of Electrophorus electricus were raised in rabbits. The antisera contain antibodies which bind to both autologous and heterologous receptors in solution as shown by an immunoprecipitation assay. Antibodies in both types of antisera bind specifically to the postjunctional membrane on the innervated surface of the intact electroplax from Electrophorus electric tissue as demonstrated by an indirect immunohistochemical procedure using horseradish peroxidase conjugated to anti-rabbit IgG. Only anti-Electrophorus receptor antisera, however, cause inhibition of the receptor-mediated depolarization of the intact Electrophorus electroplax. The lack of inhibition by anti-Torpedo receptor antibodies, which do bind, suggests that the receptor does not undergo extensive movement during activity. The binding of anti-Torpedo antibodies to receptor-rich vesicles prepared by subcellular fractionation of Torpedo electric tissue was demonstrated by both direct and indirect immunohistochemical methods using ferritin conjugates. These vesicles can be conveniently collected and prepared for electron microscopy on Millipore filters, a procedure requiring only 25 micrograms of membrane protein per filter. In addition, it was possible to visualize the binding of anti-Torpedo receptor antibodies directly, without ferritin. These anti-Torpedo receptor antibodies, however, do not inhibit the binding of acetylcholine or of alpha-neurotoxin to receptor in Torpedo microsacs but do inhibit binding of alpha-neurotoxin to Torpedo receptor in Triton X-100 solution. It is likely that the principal antigenic determinants on receptor are at sites other than the acetylcholine-binding sites and that inhibition of receptor function, when it occurs, may be due to a stabilization by antibody binding of an inactive conformational state.

Acetylcholine↗
PubMed1991

Na(+)-Ca2+ exchange activity in synaptic plasma membranes derived from the electric organ of Torpedo ocellata.

Synaptic plasma membranes obtained by hypo-osmotic treatment of purified Torpedo ocellata synaptosomes, contain an electrogenic Na(+)-Ca2+ exchange system. The dependence of the initial reaction rate on [Ca2+] reveals a single binding site for Ca2+ with an average apparent Km of 13.66 (S.D. = 12.07) microM [Ca2+] and maximal reaction velocity of Vmax = 11.33 (S.D. = 5.93) nmol/mg protein per s. The dependence of the initial rate of the Na+ gradient dependent Ca2+ influx on the internal [Na+] exhibits a sigmoidal curve which reaches half-maximal reaction rate at 170.8 (S.D. = 19.9) mM [Na+]. Addition of ATP gamma S does not change the K0.5 to Na+. The average Hill coefficient is 3.09 (S.D. = 0.86) indicating that 3-4 Na+ ions are exchanged for each Ca2+. Na+ gradient dependent Ca2+ uptake in Torpedo SPMs takes place also in the absence of K+ suggesting that K+ co-transport is not obligatory. The temperature dependence of the initial and steady-state rates of Na+ gradient dependent Ca2+ influx reveal that maximal reaction velocities of the Torpedo exchanger are attained between 15 and 20 degrees C. The energy of activation between 0 and 20 degrees C is 20,826 cal/mol. In comparison, rat brain synaptic plasma membrane Na(+)-Ca2+ exchanger reaches maximal reaction rates between 30 and 40 degrees C. Reconstitution of Torpedo or rat brain Na(+)-Ca2+ exchangers into a membrane composed of either Torpedo or brain phospholipids, does not alter the temperature dependence of the native Torpedo or rat brain Na(+)-Ca2+ exchangers; inspite of considerable differences in the composition of the fatty acyl chains that are esterified to brain and Torpedo phospholipid head groups and differences in membrane fluidity that were detected. An ATP-dependent Ca2+ pump, which is insensitive to FCCP, is also present in the same synaptic membrane.

Animals↗