title: Ca(2+)-induced Ca2+ release mediates Ca2+ transients evoked by single action potentials in rabbit vagal afferent neurones.
abstract: 1. Standard intracellular recording techniques with 'sharp' micropipettes were used to evoke action potentials (APs) in acutely dissociated adult nodose neurones. 2. APs induced a transient increase in [Ca2+]i (a calcium transient), recorded with fura-2, that was dependent upon [Ca2+]o and the number of APs. Over the range of one to sixty-five APs, the relation between the amplitude of the calcium transient and the number of APs was well fitted by a rectangular hyperbola (chi 2 = 3.53, r = 0.968). From one to four APs, the calcium transient-AP relation can be described by a line with a slope of 9.6 nM AP-1 (r = 0.999). 3. Charge movement corresponding to Ca2+ influx evoked by a single AP was 39 +/- 2.8 pC (mean +/- S.E.M.) and did not change significantly during trains of one to thirty-one APs (P < 0.05). 4. Caffeine (10 mM), a known agonist of the ryanodine receptor, produced an increase in [Ca2+]i. The caffeine-induced rise in [Ca2+]i was attenuated (by > 90%) by lowering [Ca2+]o, and by ryanodine (10 microM), 2,5-di(t-butyl)hydroquinone (DBHQ, 10 microM), or thapsigargin (100 nM). 5. Neurones incubated with ryanodine, DBHQ or thapsigargin required at least eight APs to evoke a detectable calcium transient. These reagents did not significantly affect Ca2+ influx (P < 0.05). In the presence of these inhibitors, the calcium transient-AP relation exhibited slopes of 1.2, 1.1 and 1.9 nM AP-1 for ryanodine, DBHQ and thapsigargin, respectively. When compared with the slope of 9.6 nM AP-1 in non-treated neurones, it appears that Ca2+ influx produced by a single AP is amplified by ca 5- to 10-fold.
authors.affiliation: Department of Pharmacology and Experimental Therapeutics, School of Medicine, University of Maryland, Baltimore 21201-1559, USA.
authors.forename: A S
authors.initials: AS
authors.lastname: Cohen
authors.forename: K A
authors.initials: KA
authors.lastname: Moore
authors.forename: R
authors.initials: R
authors.lastname: Bangalore
authors.forename: M S
authors.initials: MS
authors.lastname: Jafri
authors.forename: D
authors.initials: D
authors.lastname: Weinreich
authors.forename: J P
authors.initials: JP
authors.lastname: Kao
mesh_terms: D000200:Action Potentials; D000818:Animals; D002104:Cadmium / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D004594:Electrophysiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006873:Hydroquinones / Q000494:pharmacology; D008297:Male; D009475:Neurons, Afferent / Q000502:physiology*; D009620:Nodose Ganglion / Q000502:physiology*; D011817:Rabbits; D012433:Ryanodine / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology
chemical_list: D000697:Central Nervous System Stimulants; D004791:Enzyme Inhibitors; D006873:Hydroquinones; D002104:Cadmium; D012433:Ryanodine; C019359:2,5-di-tert-butylhydroquinone; D002110:Caffeine; D019284:Thapsigargin; D000252:Calcium-Transporting ATPases; D002118:Calcium