title: Calcium in sympathetic varicosities of mouse vas deferens during facilitation, augmentation and autoinhibition.
abstract: 1. The sympathetic nerve terminals of the mouse vas deferens were loaded with the calcium indicator Oregon Green 488 BAPTA-1 by orthograde transport along the postganglionic nerves. Changes in the calcium concentration in the varicosity (delta [Ca2+]v) were determined following single impulses, and short (5-impulse) and long (200-impulse) trains at 5 Hz. 2. All varicosities showed a significant delta [Ca2+]v in response to every single impulse. The elevated delta [Ca2+]v declined in two phases with similar kinetics for all varicosities: a fast phase (time constant, 0.42 +/- 0.05 s) and a moderate phase (3.6 +/- 0.4 s). 3. Line scanning confocal microscopy revealed that the delta [Ca2+] of a single terminal following single impulses was smaller for the intervaricose regions than for the varicosities. 4. Blockade of the voltage-sensitive calcium channels with Cd2+ (in calcium-free solution) completely blocked the delta [Ca2+]v on stimulation. The addition of either nifedipine (10 microM), omega-conotoxin GVIA (100 nM) or omega-agatoxin TK (100 nM) showed that 47 +/- 6% of the evoked response was mediated by N-type calcium channels. 5. Ryanodine (10 microM) did not significantly change the amplitude of delta [Ca2+]v in response to short trains. 6. Spontaneous increases in delta [Ca2+]v were observed in individual varicosities, with coupling in the increase of delta [Ca2+]v between varicosities. 7. The presynaptic alpha 2-receptor antagonist yohimbine (10 microM) increased the amplitude of delta [Ca2+]v in response to five impulses (5 Hz) by 54 +/- 14%, while the alpha 2-receptor agonist clonidine (1 microM) decreased the delta [Ca2+]v by 55 +/- 4%. 8. These results are discussed in terms of the hypotheses that the increased probability for secretion at sympathetic nerve terminals which accompanies facilitation and augmentation is due to the residual delta [Ca2+]v remaining after the calcium influx following impulses and that noradrenaline acts presynaptically to decrease the probability of secretion by modifying calcium influx.
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: D000255:Adenosine Triphosphate / Q000378:metabolism; D000320:Adrenergic Fibers / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism; D058647:Adrenergic alpha-2 Receptor Agonists; D058669:Adrenergic alpha-2 Receptor Antagonists; D000818:Animals; D017660:Autoreceptors / Q000502:physiology; D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000502:physiology; D004558:Electric Stimulation; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008807:Mice, Inbred BALB C; D009433:Neural Inhibition / Q000502:physiology*; D009638:Norepinephrine / Q000378:metabolism; D012433:Ryanodine / Q000494:pharmacology; D013565:Sympatholytics / Q000494:pharmacology; D013569:Synapses / Q000737:chemistry / Q000502:physiology*; D014649:Vas Deferens / Q000294:innervation* / Q000502:physiology*; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D058647:Adrenergic alpha-2 Receptor Agonists; D058669:Adrenergic alpha-2 Receptor Antagonists; D017660:Autoreceptors; D015220:Calcium Channels; D013565:Sympatholytics; D012433:Ryanodine; D015016:Yohimbine; D000255:Adenosine Triphosphate; D002118:Calcium; D009638:Norepinephrine