Effect of extracellular calcium on excitability of guinea pig airway vagal afferent nerves.
The effect of reducing extracellular calcium concentration ([Ca(2+)](o)) on vagal afferent excitability was analyzed in a guinea pig isolated vagally innervated trachea-bronchus preparation. Afferent fibers were characterized as either having low-threshold, rapidly adapting mechanosensors (Adelta fibers) or nociceptive-like phenotypes (Adelta and C fibers). The nociceptors were derived from neurons within the jugular ganglia, whereas the low-threshold mechanosensors were derived from neurons within the nodose ganglia. Reducing [Ca(2+)](o) did not affect the excitability of the low-threshold mechanosensors in the airway. By contrast, reducing [Ca(2+)](o) selectively increased the excitability of airway nociceptors as manifested by a substantive increase in action potential discharge in response to mechanical stimulation, and in a subset of fibers, by overtly evoking action potential discharge. This increase in the excitability of nociceptors was not mimicked by a combination of omega-conotoxin and nifedipine or tetraethylammonium. Whole cell patch recordings from airway-labeled and unlabeled neurons in the vagal jugular ganglia support the hypothesis that [Ca(2+)](o) inhibits a nonselective cation conductance in vagal nociceptors that may serve to regulate excitability of the nerve terminals within the airways.
Undem
Bradley J
BJ
Johns Hopkins School of Medicine, Department of Medicine, Baltimore, MD 21224, USA. Bundem@jhmi.edu
Oh
Eun Joo
EJ
Lancaster
Eric
E
Weinreich
Daniel
D
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D005110:Extracellular Space / Q000378:metabolism; D006168:Guinea Pigs; D008297:Male; D009413:Nerve Fibers, Myelinated / Q000502:physiology; D036421:Nerve Fibers, Unmyelinated / Q000502:physiology; D009475:Neurons, Afferent / Q000502:physiology* / Q000648:ultrastructure; D009619:Nociceptors / Q000187:drug effects / Q000502:physiology; D009620:Nodose Ganglion / Q000166:cytology / Q000502:physiology; D018408:Patch-Clamp Techniques; D010812:Physical Stimulation; D014630:Vagus Nerve / Q000166:cytology / Q000502:physiology*
D002118:Calcium