An isolated single electroplax preparation I. New data on the effect of acetylcholine and related compounds

Schoffeniels, E.; Nachmansohn, David

doi:10.1016/0006-3002(57)90047-1

Cited by 153 publications

(30 citation statements)

References 12 publications

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“…The pharmacological activities of crotoxin and of its isolated components were tested on electroplaques from Electrophorus electricus [22,23]. The cholinergic agonist carbamylcholine, usually 25 pM, was applied in the bath, on the innervated side of the cell.…”

Section: Electroplaque Experimentsmentioning

confidence: 99%

Postsynaptic Effects of Crotoxin and of Its Isolated Subunits

Bon

Changeux

Jeng

et al. 1979

European Journal of Biochemistry

209

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Crotoxin is a potent neurotoxin from the venom of Crotalus durissus terrificus. It is composed of two subunits: a basic phospholipase A2 with low toxicity (component B) and an acidic protein seemingly devoid of intrinsic biological activity (component A). Crotoxin and its isolated phospholipase subunit block the depolarisation caused by cholinergic agonists on the isolated electroplaque from Electrophorus electricus. The other component, which is inactive when applied alone, enhances the pharmacological activity of the phospholipase when the two components are used together. Crotoxin also blocks the increase of z2Na+ efflux caused by carbamylcholine from excitable microsacs prepared from Torpedo marmorata electric organ. Crotoxin therefore acts postsynaptically, but does not interfere with the binding of a-toxin from Nu@ nigricollis to the nicotinic cholinergic receptor site. Instead, like local anesthetics, it stabilizes a desensitized form of the acetylcholine receptor characterized by its high affinity for agonists. The phospholipase component B binds in a nonsaturable manner to receptor-rich membranes. In contrast, component A does not bind to acetylcholine receptor-rich membranes, but completely prevents the non-saturable binding of component B. When the two components are applied together, a saturable binding of the latter is observed with the acetylcholine receptor-rich membranes.Crotoxin, the major component of the brazilian rattle-snake (Crotalus durissus terrificus) venom is a very potent neurotoxin which possesses a phospholipase activity [l]. It is a complex of two distinct protein subunits [2,3] : a strongly basic component (component B, M , 12000) which carries the phospholipase activity and an acidic protein (component A, M , 10000) which has no enzymatic activity and is not toxic by itself. Whereas the isolated subunits are either not or only a little toxic, they recombine into a complex which exhibits the same toxicity as the original material [4,5].The lethal effect of crotoxin has generally been attributed to a presynaptic blockage of the neuromuscular transmission [6]. At this level, it causes a reduction of acetylcholine release by the nerve terminals similar to that observed with /l-bungarotoxin [7], notexin [8,9] and taipoxin [lo]. However, having observed a depression of the response to acetylcholine of the isolated denervated rat diaphragm, VitalBrazil [ l l ] concluded that crotoxin also acts at the postsynaptic level in the mammals. In order to examine a possible postsynaptic action of crotoxin without interference with its presynaptic action, we studied the effect of crotoxin on two postsynapticEnzyme. Phospholipase A2 (EC 3.1.1.4) preparations : the isolated electroplaque from Electrophorus electricus and the acetylcholine receptor-rich membranes from Torpedo marmorata. Crotoxin affects the response of both preparations to cholinergic agonists, and our observations suggest how interactions between the two subunits increase the pharmacological effect of the phospholipase component...

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Section: Electroplaque Experimentsmentioning

confidence: 99%

Postsynaptic Effects of Crotoxin and of Its Isolated Subunits

Bon

Changeux

Jeng

et al. 1979

European Journal of Biochemistry

209

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“…Slices of the Sachs' organ were cut off from live Electrophorus electricus, and single cells were disset ted following the method of Schoffeniels and Nachmansohn [8] [7]. The labeled material, which presented the same pharmacological and biochemical properties as the native toxin, had a specific radioactivity of 14.0 Ci/mmole, (0.7 mg protein/ml) or 14.8 Ci/mmole (0.408 mg protein/ml).…”

Section: Electric Organmentioning

confidence: 99%

Localization of the cholinergic receptor protein in Electrophorus electroplax by high resolution autoradiography

et al. 1972

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“…thick were cut from the posterior end of the eel as the large, widely separated and well defined dectroplaques from the organ of Sachs were required as previously described (13). A single row of dectroplaques was separated from each slice by cutting with thin scissors through the two rows of electroplaques on each side of the chosen row.…”

Section: I173 M E T H O D Smentioning

confidence: 99%

“…Only undamaged electroplaques with no visible cuts in the innervated membrane have been used in the experiments. APPARATUS A single dectroplax unit was mounted between two pools of Ringer's solution in the chamber apparatus (13). The innervated membrane was always firmly held against a window (about 8 mm.…”

Section: I173 M E T H O D Smentioning

confidence: 99%

“…The previous difficulties for the study of ion movements in electroplaques have been overcome by the method of Schoffeniels ((12); Schoffeniels and Nachmansohn (13)), in which a single isolated electroplax separates two pools of fluid. Ions can move from one pool to the other only by crossing the electroplax, and the fluxes across the conducting and non-conducting membranes can be measured separately.…”

Section: Introductionmentioning

confidence: 99%

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The Efflux of Potassium from Electroplaques of Electric Eels

Whittam

Guinnebault

1960

The Journal of General Physiology

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ABSTRACT1. T h e m o v e m e n t of labeled potassium ions has been measured across the innervated m e m b r a n e s of single isolated electroplaques, obtained from the organ of Sachs of Electrophorus electricus, m o u n t e d in an a p p a r a t u s which allowed a separate washing of the two membranes.2. Equations have been derived for a 3 c o m p a r t m e n t system in series in which tracer from a large pool in one outer c o m p a r t m e n t is collected in the other outer c o m p a r t m e n t . T h e a m o u n t of unlabeled ion in the middle c o m p a r tm e n t m a y be calculated and also the fluxes across the two membranes.3. T h e flux of potassium across the innervated m e m b r a n e s of resting cells in a steady state was between 700 to 1000 #/zmoles/cm.2/sec. and was unaffected by d-tubocurarine.4. Direct stimulation of electroplaques with external electrodes caused an increase in the effiux of potassium from the innervated m e m b r a n e of 5 to 8 /~/~moles/cm.~/impulse, which was unaffected by d-tubocurarine; no change occurred in the efflux across the non-innervated m e m b r a n e .5. It is concluded that the discharge of electroplaques is a c c o m p a n i e d by a small outward m o v e m e n t of potassium ions across the innervated m e m b r a n e of the same order of m a g n i t u d e as that found on excitation of squid giant axons. T h e d a t a show a basic similarity of potassium movements across these two entirely different types of conducting membranes and suggest that this p h e n o menon m a y be a general feature of bioelectric currents p r o p a g a t i n g an action potential.

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An isolated single electroplax preparation I. New data on the effect of acetylcholine and related compounds

Cited by 153 publications

References 12 publications

Postsynaptic Effects of Crotoxin and of Its Isolated Subunits

Postsynaptic Effects of Crotoxin and of Its Isolated Subunits

Localization of the cholinergic receptor protein in Electrophorus electroplax by high resolution autoradiography

The Efflux of Potassium from Electroplaques of Electric Eels

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