[Dual action of intracellularly released calcium on the quantal mediator secretion].
The mice diaphragm muscle and microelectrode technique were used to check the influence of ryanodine (0.5 mcM) on spontaneous and evoked mediator release under conditions of potassium depolarization (8-16 mM [K+]ex or rhythmic (4-100 Hz) stimulation of motor nerve terminals. Weak tonic calcium loading (by muscle exposition to 8 mM [K+]ex) caused a two-fold frequency increase if miniature and plate potentials (MEPPs), which was returned to the basal level by subsequent application of ryanodine. This inhibitory effect of ryanodine was blocked by apamin (500 nM) a blocker of K+(Ca)-channels. A greater calcium load of terminals (in solution with 16 mM [K+]ex) caused a 15-fold increase of MEPPs frequency. Subsequent ryanodine application caused an additional 2-3-fold increase of MEPPs frequency. During rhythmic activity of motor synapses, ryanodine was able to decrease the amplitude of EPP by 60% at plateau phase at short low frequency (4 Hz) of discharges and to increase the amplitude of EPP by 60-150% at high frequency (70-100 Hz) of discharges. It is concluded that rynodine induced calcium release from intraterminal Ca2+-stores can influence dual: excitatory or inhibitory, action on spontaneous and evoked mediator release, due to different intraterminal calcium loads and regimen of synaptic activity.
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D000818:Animals; D001030:Apamin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D003964:Diaphragm / Q000187:drug effects / Q000294:innervation / Q000378:metabolism*; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000187:drug effects; D066298:In Vitro Techniques; D051379:Mice; D008839:Microelectrodes; D009411:Nerve Endings / Q000187:drug effects / Q000502:physiology; D009469:Neuromuscular Junction / Q000187:drug effects / Q000502:physiology*; D018377:Neurotransmitter Agents / Q000378:metabolism*; D011188:Potassium / Q000502:physiology; D012433:Ryanodine / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology
D002121:Calcium Channel Blockers; D018377:Neurotransmitter Agents; D019837:Ryanodine Receptor Calcium Release Channel; D012433:Ryanodine; D001030:Apamin; D011188:Potassium; D002118:Calcium