Calcium transients evoked by action potentials in the somata of chick ciliary neurons.
The effect of action potentials on the calcium concentration in the somata of chick ciliary neurons ([Ca2+]s) was determined by loading these with the calcium indicator calcium green-1. Following trains of 1-10 impulses (30 Hz) to the postganglionic nerve, the [Ca2+]s increased rapidly and then declined along a single exponential with a time constant of 0.70 +/- 0.04 s (fast phase). After trains of 20 or 50 impulses, the elevated [Ca2+]s declined as the sum of two exponentials, with time constants of 0.78 +/- 0.12 s (fast phase) and 4.0 +/- 0.4 s (moderate phase). After a 600-impulse postganglionic train of impulses, the elevated [Ca2+]s declined quickly over about 1 s, and then as the sum of two exponentials: that of the moderate phase and a slower component with a time constant of 109 +/- 16 s (slow phase). Similar time courses were observed following stimuli to the preganglionic nerve. Caffeine (3 mM) and ryanodine (20 microM) both sped the fast phase and slowed the moderate phase of [Ca2+]s decline. Carbonyl cyanide m-chlorophenyl hydrazone (CCCP, 2 microM) slowed the slow phase, without affecting the other phases of decline. These results are discussed in relation to identifying the mechanisms responsible for these different phases of Ca2+ removal.
The Institute for Biomedical Research and The Physiology Dept., University of Sydney, NSW, Australia.
K L
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Brain
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Bennett
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D001341:Autonomic Nervous System / Q000166:cytology* / Q000378:metabolism; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D002642:Chick Embryo; D002924:Ciliary Body / Q000294:innervation*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D007476:Ionophores / Q000494:pharmacology; D008928:Mitochondria / Q000378:metabolism; D009474:Neurons / Q000737:chemistry / Q000502:physiology* / Q000648:ultrastructure; D010455:Peptides / Q000494:pharmacology; D012433:Ryanodine / Q000494:pharmacology; D017779:Sympathetic Fibers, Postganglionic / Q000187:drug effects / Q000502:physiology; D020866:omega-Conotoxin GVIA
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D000697:Central Nervous System Stimulants; D007476:Ionophores; D010455:Peptides; D012433:Ryanodine; D002110:Caffeine; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D020866:omega-Conotoxin GVIA; D002118:Calcium