Search PubMed⌕ Search

Biomedical subjects

A Mauro

Publications and source records attributed to A Mauro.

At least 73 records · Page 4Linked to original sources
PubMed1979

Reversibility and mode of action of Black Widow spider venom on the vertebrate neuromuscular junction.

Black widow spider venom (BWSV) stimulates transmitter release and depletes synaptic vesicles from muscles bathed in a sodium free medium containing 1 mM EGTA. However, frog neuromuscular junctions treated with BWSV in glucosamine Ringer's and post-treated with antivenin recover normal function. This suggests that probably the permanent block of neuromuscular transmission is due to changes in permeability of the nerve ending plasma membrane to cations such as Na+. When BWSV is applied in a medium lacking divalent cations and containing 1 mM EGTA, in most of the cases no effect is observed. We found that this inhibition can be overcome in three ways: (a) by adding divalent cations to the medium; (b) by increasing the tonicity of the medium with sucrose; (c) by raising the temperature of the medium. These results suggest that the lack of divalent cations influences the membrane fluidity. Moreover, in view of the report by Yahara and Kakimoto-Sameshima (1977. Proc. Natl. Acad. Sci. U.S.A. 74:4511--4515) that hypertonic media induce capping of surface receptors in lymphocytes and thymocytes, we think that these data further support the hypothesis that BWSV stimulates release by a dual mode of action; namely, it increases the nerve ending permeability to cations and also stimulates release directly via a process of redistribution of membrane components, a process which may also inhibit vesicle recycling.

Animals↗
PubMed1978

Effect of concanavalin A on black widow spider venom activity at the neuromuscular junction: implications for mechanisms of venom action.

Concanavalin A (Con A) inhibits black widow spider venom-induced transmitter release at both tissue-cultured and adult neuromuscular junctions and also inhibits the venom-induced destruction of cultured neurites. This inhibitory action is partially or completely prevented by prior treatment with colchicine. Neither colchicine nor Con A interacts significantly with depolarization-induced transmitter release. These results are analogous to those obtained from experiments on lymphocyte surface receptor capping. They suggest that redistribution of neuronal membrane components may be a crucial step in spider venom action. This membrane redistribution appears to be modulated in neurons, as in other cell types, by microtubule-microfilament array. How such a redistribution causes increased transmitter release cannot as yet be specified. Changes in the ionic permeability of sodium and potassium were examined as likely mechanisms. Increased sodium influx (and seondary release of calcium from intracellular stores) cannot be the basis for spider venom action. Increased potassium efflux remains a possibility, but is not consistent with all of the data. Other possible mechanisms are also suggested.

Animals↗
PubMed1978

Double mode of action of black widow spider venom on frog neuromuscular junction.

Black widow spider venom (BWSV) contains a toxin, alpha-latrotoxin, which is capable of stimulating vesicle release, resulting eventually in depletion of vesicles and block of neuromuscular transmission at the frog neuromuscular junction. Since it has been shown that alpha-latrotoxin very markedly increases the cation conductance of artificial lipid bilayers, it was postulated that BWSV stimulates release by opening channels permeable to Ca2+ and, in the case of Ca2+-free Ringer's, to Na+ which would release Ca2+ from intracellular stores. To test this hypothesis we chose as a sodium substitute, glucosamine, which is impermeable to the venom-induced channels in the lipid bilayers and to the postsynaptic membrane of the frog neuromuscular junction. Electron microscopical analysis showed that up to 75 min perfusion in Na+ and Ca2+-free medium did not alter the ultrastructure of the nerve terminals. However when BWSV was applied in this medium a significant depletion was noticeable within 15 min and after 60 min the terminals were depleted of vesicles whereas the mitochondria were unchanged in number and structure. If BWSV is applied for 60 min in glucosamine Ringer's containing 1.8 mM Ca2+, most of the nerve terminals still have synaptic vesicles scattered in the cytoplasm or clustered around amorphous structures and the mitochondria are swollen. Application of large doses of BWSV in low Ca2+ Ringer's leads to damage of the mitochondria and to very pronounced swelling of the nerve endings, whereas this is not observed if the dose of venom is applied in Na+-free and Ca2+-free Ringer's. Electrophysiological recording showed that neuromuscular transmission is already blocked after 15 min treatment with BWSV in glucosamine-Ringer's. From these results we conclude that BWSV increases the conductance of the nerve terminal membrane to cations such as Na+ and Ca2+ and stimulates release by a mechanism which may not involve its ionophore property.

Animals↗
PubMed1978

Alteration of sensitivity and time scale in invertebrate photoreceptors exposed to anoxia, dinitrophenol, and carbon dioxide.

The effects of anoxia, 2,4-dinitrophenol (DNP), and carbon dioxide (CO2) on the late receptor potential of Balanus lateral ocelli, Limulus ventral eyes, and the retinular cells of Linulus lateral eyes have been studied. Either anoxia, DNP, or exposure to 100% CO2 causes a depolarization of 5-30 mV and a gradual reduction and eventually abolition of the late receptor potential and an increase in the latency and time to peak of the response. This lengthening of the time scale is in contrast to the response obtained in photoreceptors that have been light-adapted or injected with calcium. In that case a loss in sensitivity is associated with a decrease in latency and time to peak. Because of these observed differences, the effects of metabolic inhibition cannot be attributed merely to a loss in regulation of intracellular free calcium. Rather, because alteration of intracellular pH (pHi) by using either (NH4)2SO4 or CO2 produced changes in the photoresponse similar to those caused by metabolic inhibition, it is suggested that changes in pHi during metabolic inhibition can account in part for the lengthening of the time scale. In addition to the changes in pHi and internal Ca++ concentration due to metabolic inhibition, the possible role of other consequences of metabolism in the transduction mechanism is also discussed.

Animals↗
PubMed1977

Lability of the prolonged depolarizing afterpotential in Balanus photoreceptors.

A large cell to cell variability of the prolonged depolarizing afterpotential (PDA) decay time constant (tau) has been measured in Balanus eberneus lateral ocelli. While 25% of the cells had PDA's of long duration, tau greater than 10 min. 45% of the cells tested showed either weak (tau less than 60 s) PDA or none at all. The variability was not reflected in the late receptor potential. All the cells showed normal light-coincident responses. The variability was not due to some alteration of the thermal stability of the pigment states, since after monochromatic adaptation the amplitude of the early receptor potential remained unchanged for at least 30 min. In addition, in some cells that initially showed PDAs of long duration, the decay time was either shortened or abolished after exposure to anoxia. Again, the late receptor potential and the stability of the pigments remained unaffected. These results indicate that the mechanisms which give rise to the PDA are not always tightly coupled to the direct chain of events that lead to the light-coincident response.

Action Potentials↗
PubMed1976

Purification from black widow spider venom of a protein factor causing the depletion of synaptic vesicles at neuromuscular junctions.

The aqueous extract of the venom glands of black widow spiders was fractionated on a column of Sephadex G-200 and then on a column of DEAE-Sephadex A-50 pH 8.2. A protein fraction was obtained that caused a great increase in the frequency of occurrence of miniature end plate potentials at the frog neuromuscular junction, and caused swelling of the nerve terminals and depleted them of their vesicles. The fraction consists of a least four protein components that are similar in their molecular weights (about 130,000) and isoelectric points (ranging from pH 5.2 to 5.5) and are immunologically indistinguishable. It contains no sugar residues and has little or no lipolytic or proteolytic activity. The fraction is toxic to mice and is different from the fractions that act on houseflies, the crayfish stretch receptor and the cockroach heart. It seems pure enough to warrant a detailed study of its site and mode of action.

Animals↗
PubMed1973

Turnover of transmitter and synaptic vesicles at the frog neuromuscular junction.

Curarized cutaneous pectoris nerve-muscle preparations from frogs were stimulated at 10/s or at 2/s for periods ranging from 20 min to 4 h. End plate potential were recorded intracellularly and used to estimate the quantity of transmitter secreted during the period of stimulation. At the ends of the periods of stimulation the preparations were either fixed for electron microscopy or treated with black widow spider venom to determine the quantities of transmitter remainind in the terminal. Horseradish peroxidase or dextran was added to the bathing solution and used as a tracer to detect the formation of vesicles from the axolemma. During 4 h of stimulation at 2/s many new vesicles were formed from the axolemma and the quantity of transmitter secreted was several times greater than the quantity in the initial store. After this period of stimulation, the terminals were severely depleted of transmitter, but not of vesicles, and their general morphological organization was normal. During 20 min of stimulation at 10/s the nerve terminals swelled and were severely depleted both of vesicles and of transmitter. During a subsequent hour of rest the changes in morphology were largely reversed, many new vesicles were formed from the axolemma and the stores of transmitter were partially replenished. These results suggest (a) that synaptic vesicles fuse with, and re-form from, the membrane of the nerve terminal during and after stimulation and (b), that the re-formed vesicles can store and release transmitter.

Animals↗
PubMed1972

Time-variant conductance of bilayer membranes treated with monazomycin and alamethicin.

Experimental data obtained on bilayer membranes treated with either of two antibiotics, monazomycin or alamethicin, are presented showing the marked difference in the time course of the rise and subsequent decay of the conductance in response to a positive and negative step of potential established by means of a voltage-clamp feedback circuit. The variation of the conductance with time in these model systems qualitatively mimics the behavior of the "potassium conductance" of squid giant axons and other excitable biological systems; namely, the rise of the conductance to the steady state requires a longer time than its decay to the resting state. For the alamethicin system, the decay time becomes very brief-as short as 50 musec-as either the salt or the alamethicin concentration is reduced, while the rise time remains several seconds. This marked brevity of the decay time versus the rise time may have implications for the mechanism underlying the formation of conducting channels in such membranes.

Anti-Bacterial Agents↗
PubMed1972

Changes in the fine structure of the neuromuscular junction of the frog caused by black widow spider venom.

Application of black widow spider venom to the neuromuscular junction of the frog causes an increase in the frequency of miniature end-plate potentials (min.e.p.p.) and a reduction in the number of synaptic vesicles in the nerve terminal. Shortly after the increase in min.e.p.p. frequency, the presynaptic membrane of the nerve terminal has either infolded or "lifted." Examination of these infoldings or lifts reveals synaptic vesicles in various stages of fusion with the presynaptic membrane. After the supply of synaptic vesicles has been exhausted, the presynaptic membrane returns to its original position directly opposite the end-plate membrane. The terminal contains all of its usual components with the exception of the synaptic vesicles. The only other alteration of the structures making up the neuromuscular junction occurs in the axon leading to the terminal. Instead of completely filling out its Schwann sheath, the axon has pulled away and its axoplasm appears to be denser than the control. The relation of these events to the vesicle hypothesis is discussed.

Animals↗
PubMed1972

Depletion of vesicles from frog neuromuscular junctions by prolonged tetanic stimulation.

Curarized cutaneous pectoris nerve muscle preparations from frogs were subjected to prolonged indirect stimulation at 2/sec while recording from end plate regions. At the ends of the periods of stimulation, the curare was removed and the preparations were fixed for electron microscopy or treated with black widow spider venom to determine the degree to which their stores of transmitter had been depleted. After 6-8 hr of stimulation the nerve terminals were almost completely depleted of their stores of transmitter and of their population of vesicles. Most of the transmitter release occurred during the first 4 hr of stimulation, and after this time most (about 80%) of the fibers were depleted of about 80% of their transmitter. The organization of the nerve terminals in 4-hr preparations appeared normal and the terminals still contained many vesicles. When peroxidase was present in the bathing medium, terminals from stimulated preparations showed many vesicles that contained peroxidase, whereas the rested control preparations showed few such vesicles The fact that after 4 hr the total number of vesicles is not markedly changed while a large fraction (up to 45%) contained peroxidase suggests that in our experiments vesicles were continuously fusing with and reforming from the axolemma.

Animals↗