Spontaneous miniature hyperpolarizations of presynaptic nerve terminals in the chick ciliary ganglion.
Intracellular recordings from presynaptic nerve terminals in the chick ciliary ganglion revealed the presence of spontaneous miniature hyperpolarizations in virtually all (approximately 86%) nerve terminals examined. These spontaneous events appeared as small, brief hyperpolarizations at resting potential and were observed to increase or decrease as the membrane potential was depolarized or hyperpolarized from rest, respectively. The hyperpolarizing potentials were sensitive to blockade by tetraethylammonium and Ba2+, while caffeine increased then abolished these events. The voltage fluctuations were unaffected by tetrodotoxin, low Ca2+ external solution or the synaptic blockers, picrotoxin and strychnine. These spontaneous, transient, miniature hyperpolarizations may be due to the brief and co-ordinated activation of between 15-60 Ca(2+)-dependent K+ channels following the release of Ca2+ from internal stores.
Fletcher
G H
GH
Department of Pharmacological and Physiological Science, Saint Louis University School of Medicine, MO 63104.
Chiappinelli
V A
VA
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000502:physiology; D002642:Chick Embryo; D002924:Ciliary Body / Q000187:drug effects / Q000502:physiology*; D004594:Electrophysiology; D005726:Ganglia, Parasympathetic / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D009411:Nerve Endings / Q000187:drug effects / Q000502:physiology*; D015221:Potassium Channels / Q000187:drug effects; D013779:Tetrodotoxin / Q000494:pharmacology
D015221:Potassium Channels; D002110:Caffeine; D013779:Tetrodotoxin; D002118:Calcium