The effect of papaine on the time course of the end-plate current

1980 ◽  
Vol 386 (1) ◽  
pp. 67-70 ◽  
Author(s):  
Mihaela Humar ◽  
M. Kordaš ◽  
Živa Melik
Keyword(s):  
Time Course ◽  
End Plate ◽  
Plate Current

scholarly journals An attempt at an analysis of the factors determining the time course of the end-plate current

1972 ◽  
Vol 224 (2) ◽  
pp. 317-332 ◽  
Author(s):  
M. Kordaš ◽  
I. Gabrovec ◽  
M. Kordaš ◽  
B. Popovič
Keyword(s):  
Time Course ◽  
End Plate ◽  
Plate Current

Electrical properties and innervation of fibers in the orbital layer of rat extraocular muscles

1989 ◽  
Vol 61 (1) ◽  
pp. 116-125 ◽  
Author(s):  
J. Jacoby ◽  
D. J. Chiarandini ◽  
E. Stefani
Keyword(s):  
Electrical Properties ◽  
Nerve Stimulation ◽  
Action Potentials ◽  
Time Course ◽  
Lucifer Yellow ◽  
Extraocular Muscles ◽  
Resting Potential ◽  
Inferior Rectus ◽  
End Plate ◽  
Orbital Layer

1. The inferior rectus muscle of rat, one of the extraocular muscles, contains two populations of multiply innervated fibers (MIFs): orbital MIFs, located in the orbital layer of the muscle and global MIFs, found in the global layer. The electrical properties and the responses to nerve stimulation of orbital MIFs were studied with single intracellular electrodes and compared with those of twitch fibers of the orbital layer, MIFs of the global layer, and tonic fibers of the frog. 2. About 90% of the orbital MIFs did not produce overshooting action potentials. In these fibers the characteristics and time course of the responses to nerve stimulation varied along the length of the fibers. Within 2 mm of the end-plate band of the muscle, the responses consisted of several small end-plate potentials (EPPs) and a nonovershooting spike. Distal to 2 mm, the responses in most fibers consisted of large and small EPPs with no spiking response. Some fibers produced very small spikes surmounted on large EPPs. 3. Overshooting action potentials were observed in approximately 10% of the orbital MIFs recorded between the end-plate band and 2 mm distal. The presence or absence of action potentials was not related to the magnitude of the resting potential of the fibers. 4. The threshold of nerve stimulated responses in orbital MIFs was the same as that in orbital twitch fibers. A large number of orbital MIFs had latencies equal to those for the orbital twitch fibers recorded at the same distance from the end-plate band, but the average latency was greater in the MIFs. The latency of orbital MIFs was about one-half of that for the MIFs of the global layer. The values for the effective resistance and membrane time constant of orbital MIFs fell between those for orbital twitch fibers on the one hand, and global MIFs and frog tonic fibers on the other. 5. In order to compare electrical properties with innervation patterns, fibers identified electrophysiologically as orbital MIFs were injected with the fluorescent dye Lucifer yellow and then traced in Epon-embedded, serial transverse sections. In addition to numerous superficial endings distributed along the fibers, a single "en plaque" ending was also found in the end-plate band that resembled the end plates of the adjacent orbital twitch fibers. 6. From these results we conclude that the electrical activity of orbital MIFs varies along the length of the fibers.(ABSTRACT TRUNCATED AT 400 WORDS)

A study of the effect of X-rays on the electrical properties of mammalian nerve and muscle

1963 ◽  
Vol 157 (969) ◽  
pp. 536-561 ◽  
Keyword(s):  
Dose Rate ◽  
Action Potentials ◽  
Time Course ◽  
Low Dose ◽  
High Dose ◽  
X Rays ◽  
Low Dose Rate ◽  
End Plate ◽  
Small Doses ◽  
Motor End Plate

Resting potentials, action potentials, and miniature end-plate potentials have been re­corded from isolated phrenic-diaphragm preparations of the rat during and after irradiation with X-rays. Relatively small doses of a few thousand roentgens have no obvious effect on the preparation for many hours but larger doses, of the order of 70 to 150 kr irreversibly block neuromuscular transmission. The block is not accompanied by any change in the size of action potentials, resting potentials, membrane constants or miniature potentials recorded in the muscle with intracellular electrodes, or in the size of action potentials recorded in the nerve. Records made at the motor end-plate show that the cause of the block is a ‘pre-synaptic ’ failure of impulse propagation in the intramuscular part of the nerve. The time course of the failure depends largely on the rate at which X-rays are delivered to the pre­paration: at a high dose-rate (70kr/min) the block develops rapidly and is accompanied by an increase in the frequency of miniature potentials; at a low dose-rate (7 kr/min) larger doses are required, the latency is longer and the miniature potentials continue at a normal frequency. The sequence in which different parts of the muscle become blocked, the abrupt nature of the failure at an individual motor end-plate, and the increase in frequency of the miniature potentials together suggest that the action of X-rays is to block conduction in the nerve near its terminals, possibly by depolarizing points where the axons branch and the safety factor for the propagation of impulses is low. The results reported in this paper do not support the hypotheses that small doses of X-rays at a high or a low dose-rate lead to an initial 'enhancement' of function or that they produce immediate and reversible changes in the permeability of excitable membranes to ions.

A study of curare action with an electrical micro-method

1957 ◽  
Vol 146 (924) ◽  
pp. 339-356 ◽  
Keyword(s):  
Muscle Fibre ◽  
Time Course ◽  
Inhibitory Effect ◽  
Resting Potential ◽  
Sartorius Muscle ◽  
External Application ◽  
End Plate ◽  
Motor End Plate ◽  
Close Range ◽  
Short Time

A micromethod is described by which depolarizing and inhibiting drugs can be applied, ionophoretically, from a common ‘point source’ to sensitive regions of a motor end-plate. The effects of the drugs on the membrane potential of a single end-plate are recorded, in the frog’s sartorius muscle. The antagonism between d -tubocurarine ( DTC ) and acetylcholine (or carbachol) is studied with this method. Close-range application of small quantities of the depolarizing agents (of the order of several times 10 -11 coulombs, or 10 -16 m) sets up transient potential changes of several millivolts amplitude. Application of a somewhat larger quantity of DTC (about 4 x 10 -10 C) produces a transient 50 % inhibition of the acetylcholine (or carbachol) potential. Curare does not alter the resting potential, nor the resistance or capacity of the end-plate or muscle fibre, but specifically interferes with the chemo-receptor properties of the end-plate. The inhibitory effect of DTC is obtained only with external application, but not with intracellular application from the inside of the muscle fibre. The decay of the inhibitory action of DTC is slow compared with the subsidence of the depolarization produced by acetylcholine or carbachol. The reason for this difference in time course is examined; it is probably due to relatively slow dissociation of the curare-receptor complex. Procaine in close-range, short-time application is as potent an inhibitor of acetylcholine action as DTC . The procaine effect subsides, however, much more rapidly than the action of curare.

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