A Ca2+-induced Ca2+ release mechanism involved in asynchronous exocytosis at frog motor nerve terminals

The extent to which Ca2+-induced Ca2+ release (CICR) affects transmitter release is unknown. Continuous nerve stimulation (20-50 Hz) caused slow transient increases in miniature end-plate potential (MEPP) frequency (MEPP-hump) and intracellular free Ca2+ ([Ca2+]i) in presynaptic terminals (Ca2+-hump...

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Bibliographic Details
Published in:The Journal of general physiology 1998-11, Vol.112 (5), p.593-609
Main Authors: Narita, K, Akita, T, Osanai, M, Shirasaki, T, Kijima, H, Kuba, K
Format: Article
Language:English
Subjects:
Action Potentials - physiology
Animals
Calcium - metabolism
Calcium - pharmacology
Calcium Channel Blockers - pharmacology
Chelating Agents - pharmacology
Egtazic Acid - analogs & derivatives
Egtazic Acid - pharmacology
Evoked Potentials, Motor - drug effects
Evoked Potentials, Motor - physiology
Exocytosis - drug effects
Exocytosis - physiology
Fluorescent Dyes
Gallic Acid - analogs & derivatives
Gallic Acid - pharmacology
Ion Channel Gating - drug effects
Ion Channel Gating - physiology
Magnesium - pharmacology
Motor Neurons - chemistry
Motor Neurons - cytology
Motor Neurons - metabolism
Neurotransmitter Agents - metabolism
Presynaptic Terminals - chemistry
Presynaptic Terminals - drug effects
Presynaptic Terminals - metabolism
Ranidae
Ryanodine Receptor Calcium Release Channel - metabolism
Time Factors
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Summary:The extent to which Ca2+-induced Ca2+ release (CICR) affects transmitter release is unknown. Continuous nerve stimulation (20-50 Hz) caused slow transient increases in miniature end-plate potential (MEPP) frequency (MEPP-hump) and intracellular free Ca2+ ([Ca2+]i) in presynaptic terminals (Ca2+-hump) in frog skeletal muscles over a period of minutes in a low Ca2+, high Mg2+ solution. Mn2+ quenched Indo-1 and Fura-2 fluorescence, thus indicating that stimulation was accompanied by opening of voltage-dependent Ca2+ channels. MEPP-hump depended on extracellular Ca2+ (0.05-0.2 mM) and stimulation frequency. Both the Ca2+- and MEPP-humps were blocked by 8-(N, N-diethylamino)octyl3,4,5-trimethoxybenzoate hydrochloride (TMB-8), ryanodine, and thapsigargin, but enhanced by CN-. Thus, Ca2+-hump is generated by the activation of CICR via ryanodine receptors by Ca2+ entry, producing MEPP-hump. A short interruption of tetanus (
ISSN:0022-1295
1540-7748
DOI:10.1085/jgp.112.5.593