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. 1990 May;100(1):114–118. doi: 10.1111/j.1476-5381.1990.tb12061.x

Ryanodine facilitates calcium-dependent release of transmitter at mouse neuromuscular junctions.

M Nishimura 1, K Tsubaki 1, O Yagasaki 1, K Ito 1
PMCID: PMC1917448  PMID: 1973623

Abstract

1. Quantal release of transmitter was measured intracellularly at mouse neuromuscular junctions in the presence and absence of ryanodine (Rnd). 2. Rnd at concentrations up to 1 microM did not significantly alter the frequency of miniature endplate potentials (m.e.p.ps) in the presence or absence of Ca2+, suggesting that Rnd is unlikely to alter the internal concentration of Ca2+ ([Ca2+]i) at rest. 3. In a high-K+ (10 mM) bathing solution, Rnd further potentiated the facilitatory effect of Ca2+ on the frequency (F, s-1) of m.e.p.ps. Rnd shifted the relationship between 1n(F) and 1n[Ca2+]o to lower concentrations. 4. In a high-Mg2+ bathing solution, Rnd did not affect the frequency of m.e.p.ps at any value of [Ca2+]o. However, Rnd slightly but significantly increased the quantal content (m) of e.p.ps. It shifted the relationship between 1n(m) and 1n[Ca2+]o to lower concentrations. These results suggest that Rnd potentiates the quantal release of transmitter after depolarization of the membrane or nerve impulse, in keeping with the cooperativity of Ca2+ at the active site. 5. A series of two closely spaced nerve impulses produced a facilitation of transmitter release, as judged by the quantal content (m2) of the second response in relation to that of the first one (m1), m2/m1. Rnd did not change the ratio m2/m1. Thus Rnd is unlikely to affect the rapid phase of the sequestration of Ca2+ inside the nerve terminal. 6. High levels of K+ (5 mM) and caffeine (2 mM) potentiated both modes of transmitter release, in a manner dependent on [Ca2+]o. Caffeine did not potentiate facilitation of transmitter release.(ABSTRACT TRUNCATED AT 250 WORDS)

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Selected References

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