title: Calcium in the nerve terminals of chick ciliary ganglia during facilitation, augmentation and potentiation.
abstract: 1. The calyciform nerve terminals of chick ciliary ganglia were loaded with the calcium indicators calcium green 1 or fura-2. These were used to determine the change in calcium concentration in the terminal, [Ca2+]t, following short (10 impulses) and long (600 impulses) trains of high-frequency (30 Hz) stimulation. 2. Following a single impulse or a short train, the elevated [Ca2+]t declined along two exponentials with time constants similar to slow (F2) facilitation (0.52 s) and augmentation (4.0 s). After a long train elevated [Ca2+]t declined eventually along a single exponential with the time constant of post-tetanic potentiation (162 s). [Ca2+]t was not elevated through long-term potentiation. 3. Addition of Ba2+ (0.75 mM) to the extracellular solution slowed only the decline of [Ca2+]t associated with augmentation. The addition of the nitric oxide donor sodium nitroprusside did not affect [Ca2+]t following short or long trains. 4. Removal of extracellular calcium (buffered with EGTA) and the blockade of calcium channels with Cd2+ completely prevented the changes in [Ca2+]t. 5. The soma of ciliary ganglion cells were loaded with calcium green and the postganglionic nerves stimulated with a single impulse or a short train of impulses. Following stimuli, the elevated [Ca2+]t declined along a single exponential with a time constant similar to F2 facilitation with no augmentation component evident. 6. The results are discussed in terms of the hypothesis that each impulse in a train gives an equal increment of residual Ca2+ to a compartment for secretion and that Ca2+ is removed from the compartment by three first-order kinetics processes associated with F2 facilitation, augmentation and post-tetanic potentiation.
authors.affiliation: Department of Physiology F13, University of Sydney, NSW, Australia.
authors.forename: K L
authors.initials: KL
authors.lastname: Brain
authors.forename: M R
authors.initials: MR
authors.lastname: Bennett
mesh_terms: D000818:Animals; D001464:Barium / Q000494:pharmacology; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002642:Chick Embryo; D004558:Electric Stimulation; D005456:Fluorescent Dyes; D016257:Fura-2; D005726:Ganglia, Parasympathetic / Q000166:cytology / Q000502:physiology*; D017774:Long-Term Potentiation / Q000502:physiology; D008856:Microscopy, Fluorescence; D009411:Nerve Endings / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology*; D009569:Nitric Oxide / Q000494:pharmacology; D009802:Oculomotor Nerve / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D009930:Organic Chemicals
chemical_list: D002121:Calcium Channel Blockers; D005456:Fluorescent Dyes; D009930:Organic Chemicals; D002104:Cadmium; C071336:calcium green; D001464:Barium; D009569:Nitric Oxide; D002118:Calcium; D016257:Fura-2