Premium
Ryanodine facilitates calcium‐dependent release of transmitter at mouse neuromuscular junctions
Author(s) -
Nishimura Masakazu,
Tsubaki Kikuko,
Yagasaki Osamu,
Ito Katsuaki
Publication year - 1990
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1990.tb12061.x
Subject(s) - ryanodine receptor , depolarization , chemistry , calcium , biophysics , neuromuscular junction , extracellular , endocrinology , biology , biochemistry , neuroscience , organic chemistry
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 μ m did not significantly alter the frequency of miniature endplate potentials (m.e.p.ps) in the presence or absence of Ca 2+ , suggesting that Rnd is unlikely to alter the internal concentration of Ca 2+ ([Ca 2+ ] i ) at rest. 3 In a high‐K + (10 m m ) bathing solution, Rnd further potentiated the facilitatory effect of Ca 2+ on the frequency (F, s −1 ) of m.e.p.ps. Rnd shifted the relationship between ln(F) and ln[Ca 2+ ] o to lower concentrations. 4 In a high‐Mg 2+ bathing solution, Rnd did not affect the frequency of m.e.p.ps at any value of [Ca 2+ ] o . However, Rnd slightly but significantly increased the quantal content (m) of e.p.ps. It shifted the relationship between ln(m) and ln[Ca 2+ ] 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 Ca 2+ 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 Ca 2+ inside the nerve terminal. 6 High levels of K + (5 m m ) and caffeine (2 m m ) potentiated both modes of transmitter release, in a manner dependent on [Ca 2+ ] o . Caffeine did not potentiate facilitation of transmitter release. 7 These results indicate that Rnd facilitates the quantal release of transmitter presumably via an increase in [Ca 2+ ] i by a manner different from that of high‐K + or caffeine. The results suggest that Rnd probably affects calcium turnover in neuronal cells.