Biomedical subjects

D Pauron

Publications and source records attributed to D Pauron.

23 records · Page 2Linked to original sources

PubMed1985

A monoclonal immunotoxin acting on the Na+ channel, with properties similar to those of a scorpion toxin.

We describe the properties of a monoclonal antibody against the Na+ channel. The antibody, 72.38, competitively inhibited (Ki = 1.5 X 10(-9) M) the binding of an 125I-labeled toxin from the Brazilian scorpion Tityus serrulatus (125I-TiTX gamma) to Na+ channels of rat brain membranes. No significant inhibition of binding of a number of other Na+ channel toxins was observed. The inhibition of 125I-TiTX gamma binding also was observed with the solubilized Na+ channel from rat brain membranes (Ki = 2 X 10(-9) M). Antibody 72.38 antagonized 125I-TiTX gamma binding to Na+ channels from different animal species (fish, avian, and mammalian) and from different tissues (electroplax, brain, heart, and muscle). Moreover, 72.38 has been used for immunofluorescence labeling of Na+ channels in rat sciatic nodes of Ranvier and cultured dorsal root ganglion cells. Electrophysiological experiments on rat muscle cells fully confirmed the similarity between TiTX gamma and 72.38 seen in binding experiments. Both produce slow oscillations of the membrane potential accompanied by bursts of action potentials which are due to a selective action on the Na+ channel. TiTX gamma and 72.38 are without effect on the ion selectivity of the Na+ channel, but they both drastically change the voltage-dependence of activation and inactivation of the Na+ channel.

Animals↗

PubMed1984

Reconstitution of highly purified saxitoxin-sensitive Na+-channels into planar lipid bilayers.

Highly purified Na+-channels isolated from rat brain have been reconstituted into virtually solvent-free planar lipid bilayer membranes. Two different types of electrically excitable channels were detected in the absence of any neurotoxins. The activity of both channels was blocked by saxitoxin. The first channel type is highly selective for Na+ over K+ (approximately 10:1), it shows a bursting behavior, a conductance of 25 pS in Na+-Ringer and undergoes continuous opening and closing events for periods of minutes within a defined range of negative membranes voltages. The second channel type has a conductance of 150 pS and a lower selectivity for Na+ and K+ (2.2:1); only a few opening and closing events are observed with this channel after one voltage jump. The latter type of channel is also found with highly purified Na+-channel from Electrophorus electricus electroplax. A qualitative analysis of the physicochemical and pharmacological properties of the high conductance channel has been carried out. Channel properties are affected not only by saxitoxin but also by a scorpion (Centruroides suffusus suffusus) toxin and a sea anemone (Anemonia sulcata) toxin both known to be selective for the Na+-channel. The spontaneous transformation of the large conductance channel type into the small one has been considered; the two channel types may represent the expression of activity of different conformational states of the same protein.

Animals↗

PubMed1984

The effect of Tityus serrulatus scorpion toxin gamma on Na channels in neuroblastoma cells.

The effects of highly purified toxin gamma from the venom of the scorpion Tityus serrulatus (TiTx gamma) on nerve membrane ionic channels have been investigated using the suction electrodes voltage clamp technique on neuroblastoma cells. The amplitude of the normally voltage-dependent Na current is reversible reduced by approximately 50% after 15-105 nM TiTx gamma, whereas even the highest toxin concentrations have no significant effect on the outward K current in the presence of tetrodotoxin. TiTx gamma causes a transient inward current to appear at membrane potentials between -70 and -40 mV, a potential region in which no significant inward current is observed in control experiments. Tetrodotoxin (300 nM) rapidly blocks both the TiTx gamma-induced inward current and the remaining normally voltage-dependent Na current. The binding of radiolabelled TiTx gamma to the Na channels in the neuroblastoma cell membrane is prevented by native TiTx gamma with a K0.5 = 0.75 nM. Both activation and inactivation of the TiTx gamma-induced Na current are shifted 30-40 mV towards more negative potential values as compared to normally voltage-dependent Na current. The TiTx gamma-induced Na current exhibits sigmoidal activation kinetics and relatively slow, exponential inactivation kinetics. The local anesthetic procaine at an external concentration of 1 mM blocks more effectively the remaining normally voltage-dependent Na current than the TiTx gamma-induced Na current. Both Na current components are equally blocked by 1 mM of the local anesthetic propoxycaine. The relation between the effects of TiTx gamma on Nat channels and those of other known neurotoxins those of other known neurotoxins specific of this channel is discussed.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthetics, Local↗

PubMed1984

New scorpion toxins with a very high affinity for Na+ channels. Biochemical characterization and use for the purification of Na+ channels.

Biochemical characterization of the Tityus gamma toxin receptor associated with the voltage-sensitive Na+ channel was carried out in different tissue preparations with the use of an iodinated toxin derivative. The affinity of the toxin for the receptor is high with a dissociation constant of 4 X 10(-12) M for rat synaptosomes. The density of binding sites is in the range of 0.3 to 2 pmol/mg of protein. Toxin gamma does not seem to bind to Na+ channels located on transverse-tubule membranes of skeletal muscle, but only to Na+ channels located on the sarcolemma. Both affinity labelling and radiation inactivation analysis indicate a molecular weight for the toxin receptor of 270 000 daltons. The same molecular weight is found using the tetrodotoxin. Only one single major protein component of the Na+ channel was purified from Electrophorus electroplax, rat brain membranes and chick heart membrane using the toxin gamma as a marker. The molecular weight of this component is 230 000-270 000 daltons. Reconstitution of the purified Na+ channel into planar lipid bilayers has been carried out. Two different types of electrically excitable channels with conductances of 150 and 25 pS were detected. The activity of both channels is blocked by saxitoxin.

Animals↗

PubMed1983

Electrophysiological characterization, solubilization and purification of the Tityus gamma toxin receptor associated with the gating component of the Na+ channel from rat brain.

Electrophysiological studies with neuroblastoma cells have shown that toxin gamma from the venom of the scorpion Tityus serrulatus is a new toxin specific for the gating system of the Na+ channel. The procedure which solubilizes the tetrodotoxin receptor from rat brain also solubilizes the Tityus gamma toxin receptor. Binding experiments on the solubilized receptor with a radioiodinated derivative of Tityus gamma toxin have shown: (i) that the TiTx gamma-receptor complex is very stable with a dissociation constant of 8.6 X 10(-12) M and a very slow dissociation (T 1/2 = 15 h); (ii) that the toxin recognizes a class of sites with a 1:1 stoichiometry with those for tetrodotoxin (Bmax = 1.3 pmol/mg protein). The radioiodinated Tityus gamma-receptor complex has been substantially purified by ion-exchange chromatography, lectin affinity chromatography and sucrose gradient sedimentation. A ratio of one Tityus gamma toxin binding site per tetrodotoxin binding site was found throughout the purification. The purified material exhibited a sedimentation coefficient of 10.4S and had an apparent mol. wt. of 270 000 on SDS-gel electrophoresis. No other polypeptide chains were demonstrated to be associated with this large protein in the Tityus gamma receptor. The main conclusion is that the tetrodotoxin binding site associated with the selectivity filter of the Na+ channel and the Tityus gamma toxin binding site associated with the gating component are probably carried by the same polypeptide chain.

Action Potentials↗