Effects of physiologic alterations on binomial transmitter release at magnesium‐depressed neuromuscular junctions.

Abstract

1. Transmitter release from Mg2+‐treated frog neuromuscular junctions can be described by binomial statistics. Good agreement between the observed amplitude‐frequency distribution of e.p.p.s. and that predicted by binomial statistics is observed with relatively low concentrations of Mg2+. Conversely, good agreement is found with Poisson predictions when higher concentrations of Mg2+ are used to depress transmission. 2. Binomial analysis at these junctions shows that Mg2+ reduces quantal content (m), the probability of release (p) and to a lesser extent the available stores of transmitter (n). Raising Ca2+ causes an increase in n and p and a small but significant increase in n. K+ increases m and p but not n. 3. During 'frequency‐facilitation' (1‐6 Hz), e.p.p.s., m and n are increased but p is unaffected. 4. It is concluded that binomial statistics can be used to estimate the quantal parameters of transmitter release and that these parameters can be identified as discrete entities.

Voltage clamping of unparalysed cut rat diaphragm for study of transmitter release.

“…These results stand in contrast to those of Takeuchi & Takeuchi (1961) and Branisteanu, Miyamoto & Volle (1976) which indicated an increase in quantal content when external K+ was raised from 2-5 to 10*0 mm. However, their experiments were performed on Mg2+-depressed junctions, which may well behave differently.…”

Do Motor‐nerve Terminals Have Γ‐aminobutyric Acid Receptors?

“…Quantal content would have to be reduced by approximately 20% to obtain significance at the 5% level. Further the relationship between terminal depolarization and m may be more complex than assumed, since elevation of K + increases m (Tak-euchi & Takeuchi, 1961;Edwards & Ikeda, 1962;Branisteanu, Miyamoto & Volle, 1976), whereas acetylcholine decreases m (Hubbard et al, 1965). However, in the bullfrog sympathetic ganglion, GABA (0.1 to 1 mM) decreased m by approximately 42%, a decrease which should have been resolvable by the present techniques (Kato, Kuba & Koketsu, 1978).…”

Clumping and oscillations in evoked transmitter release at the frog neuromuscular junction.

“…The present work is a time series analysis of the fluctuations in the evoked synaptic potentials amplitude at the neuromuscular junction. This analysis demonstrates the existence of a process which introduces an element of 'order', superimposed on the random discharge of transmitter quanta (del Castillo & Katz, 1954;Martin, 1955Martin, , 1966Johnson & Wernig, 1971;Wernig, 1972;Zucker, 1973;Bennet & Florin, 1974;Branisteanu, Miyamoto & Volle, 1976). The more common manifestation of this process is the clumping of synaptic potentials of similar amplitude; under restricted experimental conditions, this clumping is periodic and appears as oscillations.…”