Noradrenaline synchronizes evoked quantal release at frog neuromuscular junctions.
1. Noradrenaline (NA) increases synaptic efficacy at the frog neuromuscular junction. To test the hypothesis that one of the actions of NA is to shorten the period over which evoked quanta are released, we measured the latencies of focally recorded uniquantal endplate currents (EPCs). 2. NA shortened the release period for evoked quantal release. The interval between the time when responses with minimal delay appeared and the point at which 90 % of all latencies had occurred was shortened in the presence of 1 x 10-5 M NA by about 35 % at 20 C and by about 45 % at 8 C. Inhibitor and agonist experiments showed that NA acts on a beta-adrenoreceptor. 3. The better synchronization of release significantly increased the size of reconstructed multi- quantal EPCs. This suggests that NA facilitates synaptic transmission by making the release of quanta more synchronous. 4. The synchronizing action of NA might potentiate neuromuscular transmission during nerve regeneration, transmitter exhaustion and other extreme physiological states where the quantal content is reduced, such as survival in cold and hibernation.
Bukcharaeva
E A
EA
Kazan State Medical University and Kazan Institute of Biology, Academy of Sciences, Kazan, Russian Federation.
Kim
K C
KC
Moravec
J
J
Nikolsky
E E
EE
Vyskocil
F
F
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D005071:Evoked Potentials / Q000187:drug effects / Q000502:physiology; D066298:In Vitro Techniques; D009045:Motor Endplate / Q000187:drug effects / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation*; D009469:Neuromuscular Junction / Q000187:drug effects / Q000502:physiology*; D009638:Norepinephrine / Q000494:pharmacology*; D011789:Quantum Theory; D011895:Rana ridibunda; D011930:Reaction Time; D011943:Receptors, Adrenergic, beta / Q000502:physiology; D012044:Regression Analysis; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D009435:Synaptic Transmission
D000316:Adrenergic alpha-Agonists; D000318:Adrenergic beta-Agonists; D011943:Receptors, Adrenergic, beta; D009638:Norepinephrine