Chemosensitivity of nociceptive, mechanosensitive afferent nerve fibres in the guinea-pig ureter.
The mechanosensitivity and chemosensitivity of afferent fibres were investigated in an in vitro preparation of the guinea-pig ureter. Electrophysiological recordings were obtained from 5 U-1 (low mechanical threshold, contraction-sensitive) and 74 U-2 units (high threshold). U-2 units had significant higher levels of spontaneous activity, lower conduction velocities, higher mechanical thresholds (U-1: 7 mmHg; U-2: 39 mmHg), less pronounced phasic responses and longer latencies in the response to distensions than the U-1 units. For chemical stimulation, guinea-pig urine (> 800 mosmol/L), bradykinin and capsaicin were applied intraluminally. The responses of U-1 units mainly corresponded to the contractions induced by the chemical stimulation. The vast majority of the U-2 units were excited by urine, bradykinin (threshold: 0.1-1 microM) and capsaicin (threshold: 0.03-0.3 microM). The responses to urine could be mimicked by high concentrations of potassium ions (> 200 mM), but not by an equiosmolar solution of NaCl, urea and mannitol. Chemical stimulation could also result in a transient sensitization of the U-2 units to mechanical stimuli. In the anaesthetized guinea-pig, pseudo-affective responses could be evoked by ureteric distension (threshold: 30-60 mmHg) and serosal application of capsaicin. Intraluminal application of urine in vivo did not evoke any reactions, suggesting that the responses of the U-2 units to urine might be due to an impaired barrier function of the urothelium in vitro. The data are in agreement with the hypothesis that U-2 units are visceral polymodal nociceptors. Since the U-1 units were also able to encode at least noxious mechanical stimuli, their involvement in visceral nociception cannot be excluded.
Sann
H
H
Physiologisches Institut, Tierärztliche Hochschule, Hannover, Germany. hsann@physiology.tiho-hannover.de
D000344:Afferent Pathways / Q000187:drug effects; D000818:Animals; D001920:Bradykinin / Q000494:pharmacology; D002211:Capsaicin / Q000494:pharmacology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008465:Mechanoreceptors / Q000187:drug effects*; D009412:Nerve Fibers / Q000187:drug effects*; D009619:Nociceptors / Q000187:drug effects*; D011930:Reaction Time / Q000187:drug effects; D013268:Stimulation, Chemical; D014513:Ureter / Q000294:innervation*; D014556:Urine
D002211:Capsaicin; D001920:Bradykinin