Neuromuscular transmission in a mammalian preparation in the absence of blocking drugs and the effect of D‐tubocurarine

Abstract

SUMMARY1. Neuromuscular transmission in the presence and absence of D-tubocurarine was examined in cut muscle preparations of the rat diaphragm using intracellular recording techniques. The method of localizing the endplates is described and evidence is presented indicating that end-plate potential (e.p.p.) recordings were made close to the end-plate region and that reliable estimates of the quantum content of e.p.p.s could be made.2. During repetitive nerve stimulation at rates between 2 and 10 Hz, e.p.p. amplitudes declined in response to the first 6-8 stimuli to reach a plateau level which was maintained for 1500 stimuli. At higher rates of stimulation some 500-700 stimuli were needed before a plateau level of amplitude was reached. It was demonstrated that these amplitude changes reflected similar changes in the quantal release of ACh. 3. Tubocurarine in a concentration of 4 x 10-g/ml. had no effect on quantal release but did reduce quantal size. In the presence of tubocurarine, 8 x 10-g/ml., small reductions in the quantum content of the first e.p.p. in response to a train of stimuli and the maintained quantal release were observed. In the presence of tubocurarine 4 x 10-7 g/ml., the quantum content of the first e.p.p. and the maintained release were further reduced, to the level previously described for curarized preparations. At this concentration a significant effect of tubocurarine upon the presynaptic measurements could be detected (t test). Studies on single junctions revealed that the post-and presynaptic effects of tubocurarine developed with different time courses.4. Neuromuscular preparations in vivo have been reported to be much more resistant to maintained stimulation than curarized neuromuscular J.

Changes in total and quantal release of acetylcholine in the mouse diaphragm during activation and inhibition of membrane ATPase.

“…In eight experiments, however, we compared changes in both types of released transmitter during a 10 min period of stimulation hoping to estimate, at least approximately, the proportion of quantal and total release of transmitter. For the electrophysiological estimation of quantal release, a sectioned preparation (Hubbard et al 1969;Hubbard & Wilson, 1973 (Fig. 6).…”

Acetylcholine compartments in mouse diaphragm. Comparison of the effects of black widow spider venom, electrical stimulation, and high concentrations of potassium.

“…The average wet weight of a hemidiaphragm without ribs was 22 mg (range [16][17][18][19][20][21][22][23][24][25][26][27][28][29]; the average wet weight of a hemidiaphragm with ribs was 85 mg.…”

“…Their calculation assumed an epp to be composed of 400 quanta. A more reasonable figure would be 200-300 (19). If the latter figures are used, the number of molecules in a quantum would lie between 9 and 12 x 10 3 .…”

The origin of the effects of an anticholinesterase on the latencies of action potentials in mouse skeletal muscles

“…The saline was gassed with a mixture of 95% 02 and 5% CO2 and the temperature was maintained at 37.0 ± 0.50C. The (Barstad, 1962;Hubbard & Wilson, 1973 Recording of miniature endplate potentials and endplate potentials Miniature endplate potentials and endplate potentials were recorded on an FM tape recorder and on replay were displayed on an oscilloscope and were analysed on-line using an analogue-to-digital converter and a PDP 11/03 minicomputer. The recording of miniature endplate potentials with a rise-time to amplitude ratio of less than 1.1 ms/mV was the criterion for the focal location of the microelectrode at the endplate.…”