Post‐synaptic potentiation: interaction between quanta of acetylcholine at the skeletal neuromuscular synapse.

Hartzell, H. Criss; Kuffler, Stephen W.; Yoshikami, Doju

doi:10.1113/jphysiol.1975.sp011102

Cited by 250 publications

(207 citation statements)

References 35 publications

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“…We confirm (12)(13)(14)(15) that inactivation of esterases lengthens tf appreciably and that, when cr is reduced by BTX treatment, tf is somewhat shortened again (12,15). Our additional observations are that, when esterases are intact, tf does not depend on Ac ( Fig.…”

Section: Resultssupporting

confidence: 73%

Diffusion and binding constants for acetylcholine derived from the falling phase of miniature endplate currents.

Land¹,

Harris²,

Salpeter³

et al. 1984

Proc. Natl. Acad. Sci. U.S.A.

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In previous papers we studied the rising phase of a miniature endplate current (MEPC) to derive diffusion and forward rate constants controlling acetylcholine (AcCho) in the intact neuromuscular junction. The present study derives similar values (but with smaller error ranges) for these constants by including experimental results from the fallins phase of the MEPC. We find diffusion to be 4 x 10-6 cm2 slightly slower than free diffusion, forward binding to be 3.3 x 107 M-s-, and the distance from an average release site to the nearest exit from the cleft to be 1.6 jtm. We also estimate the back reaction rates. Heidmann and Changeux (7).] In our approach we use the shape of the MEPC as a function of AcChoR concentration to derive forward binding rates as well as information on AcCho diffusion in the intact neuromuscular cleft. We thus complement the results obtained by chemical techniques and by single-channel recording. The derived parameters support our motivating assumptions of the "saturating disk model" used by Salpeter and colleagues (8-11) to explain the generation of the MEPC. METHODSWe recorded MEPCs by voltage clamp from the intercostal muscle of the lizard Anolis carolinensis, using experimental techniques as in the first two papers of this series (1, 2) with minor modifications.Three groups were used: (i) control muscle (esterases and receptor concentration unaltered); (ii) receptors intact and esterases fully inactivated [with 1 mM diisopropyl fluorophosphate (iPr2P-F) for 1 hr]; (iii) receptors partially inactivated [with 40 nM a-bungarotoxin (BTX) for 40 min] to -0.36 its normal value (papers 1 and 2) and esterases inactivated with iPr2P-F as in ii. The filtering conditions of the voltage clamp were modified from those used in papers 1 and 2 to improve the signal-to-noise ratio. Because the falling phase of MEPCs is slow relative to the rise time, the signals were low-pass-filtered at 1 kHz (two-pole Butterworth filter) and the digitizer sampling rate was reduced to 6.25 kHz. Even though the Nyquist frequency is only a factor of 3 above our filter cutoff, aliasing was judged to be less than 4% of peak current. All experiments were done at 22 ± 10C and -100 mV holding potential. Fall time (tf) values were obtained from the experimental MEPC as 1.23 x the 90-40% fall time. The factor 1.23 is the conversion from 90-40% to efolding time for a pure exponential. Fig. 1 shows six examples of measured MEPC traces, illustrating the three conditions used in the present study. Fig. 2 plots the relation between tf and MEPC amplitude Ac, and Table 1 gives the mean values of tf and Ac under these conditions. RESULTSWe confirm (12-15) that inactivation of esterases lengthens tf appreciably and that, when cr is reduced by BTX treatment, tf is somewhat shortened again (12, 15). Our additional observations are that, when esterases are intact, tf does not depend on Ac ( Fig. 2A), but after esterase inactivation tf increases with increasing Ac (Fig. 2B). Finally, decreasing a, with esterases inactivated, alm...

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Section: Resultssupporting

confidence: 73%

Diffusion and binding constants for acetylcholine derived from the falling phase of miniature endplate currents.

Land¹,

Harris²,

Salpeter³

et al. 1984

Proc. Natl. Acad. Sci. U.S.A.

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“…Co-operativity appears to be a general feature of the interaction of neural transmitters and their receptors (Werman, 1969;Takeuchi & Takeuchi, 1969;Feltz, 1971;Brookes & Werman, 1973;Hartzell, Kuffler & Yoshikami, 1975;Constanti, 1977). However, the mechanism of this phenomenon has not been established.…”

Section: Discussionmentioning

confidence: 99%

Conductance increases produced by glycine and gamma‐aminobutyric acid in lamprey interneurones.

Homma¹,

Rovainen²

1978

The Journal of Physiology

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SUMMARY1. Conductances of individual neurones in the isolated lamprey spinal cord were measured with separate intracellular electrodes for recording potentials and for passing current pulses during application of glycine or GABA (0.1-1.0 mM) in Cafree bathing fluid. Large, reversible increases in conductance were produced in giant interneurones by both amino acids, but Muller axons and sensory dorsal cells were unaffected.2. Conductance increases produced by glycine and by GABA were selective for C1. Both conductance increases were linearly related to external Cl concentrations and repeated exposure to the amino acids in Cl-free fluid progressively reduced the conductance increases to less than 1 % of their values in normal C1.3. Strychnine was a competitive antagonist of glycine, while GABA was antagonized competitively by bicuculline and non-competitively by picrotoxin.4. The sensitivity of giant interneurones to glycine and GABA increased at low temperatures, in Na-free fluid, and after repeated exposure to the amino acids. Sensitization may have been produced by inhibition of uptake mechanisms for glycine and GABA in the spinal cord.5. Discharges of interneurones recorded extracellularly were inhibited by bathapplied glycine and GABA, but directly elicited action potentials of axons were ,unaffected. Strychnine and Cl-free fluid in the presence of Ca produced seizures in lamprey spinal cord.6. The conclusions of these experiments are that different receptors for glycine and for GABA are present on giant interneurones, that glycine is the better candidate for an inhibitory transmitter in the lamprey spinal cord, and that GABA produces effects similar to those which have been well studied in arthropod muscle.

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“…The question of whether ACh saturates the receptor during a neuromuscular response has been considered in numerous publications (e.g. Salpeter & Eldefrawi, 1973;Hartzell et al 1975;Negrete, del Castillo, Escobar & Yankelevich, 1972a, b;Barnard et al 1975) with differing conclusions. Much of the difference stems from the various definitions of saturation used in these studies.…”

Section: Discussionmentioning

confidence: 99%

Distribution of acetylcholine receptors at frog neuromuscular junctions with a discussion of some physiological implications.

Matthews-Bellinger¹,

Salpeter²

1978

The Journal of Physiology

214

124

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SUMMARY1. The distribution of acetylcholine receptors (AChR) at frog cutaneous pectoris neuromuscular junctions was studied quantitatively using [125I]a-bungarotoxin (a-BTX) labelling and EM autoradiography.2. We found that, as in mouse end-plates, the AChR is localized uniformly along the thickened post-junctional membrane. In the frog muscle this specialized membrane constitutes approximately the top 50 % of the junctional folds.3. The receptor site density is 26,000 + 6000 sites/,um2 on the thickened postjunctional membrane and falls sharply to 50 sites/fum2 within 15 Itm from the axon terminal.4. a-BTX site density on the presynaptic axonal membrane was directly determined to be at most 5 % of the value on the thickened post-junctional membrane.5. The high post junctional AChR site density leads us to conclude that: (a) each quantum of ACh needs to spread only over a very small post-junctional area (to be called the 'critical area') before it encounters as many AChR (plus AChE) sites as there are ACh molecules in the quantum (for a packet of 104 ACh molecules this critical area is-03 #um2), (b) the average concentration of ACh prevailing in

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Post‐synaptic potentiation: interaction between quanta of acetylcholine at the skeletal neuromuscular synapse.

Cited by 250 publications

References 35 publications

Diffusion and binding constants for acetylcholine derived from the falling phase of miniature endplate currents.

Diffusion and binding constants for acetylcholine derived from the falling phase of miniature endplate currents.

Conductance increases produced by glycine and gamma‐aminobutyric acid in lamprey interneurones.

Distribution of acetylcholine receptors at frog neuromuscular junctions with a discussion of some physiological implications.

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