Stimulation of pulmonary C fibres by lactic acid in rats: contributions of H+ and lactate ions.
1. The contributions of H+ and lactate ions to the stimulation of single pulmonary C fibres by lactic acid were examined in anaesthetized and artificially ventilated rats. 2. Lactic acid injected into the right atrium caused a transient decrease in arterial blood pH (pHa) and a short but intense burst of afferent activities in pulmonary C fibres, whereas sodium lactate had no effect. The fibre activity usually reached a peak within 1-1.5 s, with an onset latency of < 1 s, and returned to the baseline in 5 s. 3. The injection of hydrochloric acid at the same pH as that of lactic acid did not significantly decrease pHa, nor did it stimulate any C fibres studied. 4. Formic acid has a pKa value (the negative logarithm of the dissociation constant) almost identical to that of lactic acid; thus, its injection decreased pHa to the same degree as did the injection of lactic acid. However, the response of C fibres to lactic acid was 134% stronger than that to formic acid. 5. We conclude that H+ is primarily responsible for the activation of pulmonary C fibres by lactic acid, probably through a direct effect of H+ on these afferent endings. The lactate ion, by itself, does not activate C fibres, but it seems to potentiate the stimulatory effect of H+ on these afferents.
Hong
J L
JL
Department of Physiology, University of Kentucky Medical Center, Lexington 40536-0084, USA.
Kwong
K
K
Lee
L Y
LY
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002319:Cardiovascular System / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D005561:Formates / Q000494:pharmacology; D006325:Heart Atria; D006490:Hemostatics / Q000494:pharmacology; D006851:Hydrochloric Acid / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D019344:Lactic Acid / Q000494:pharmacology*; D008168:Lung / Q000294:innervation*; D008297:Male; D009412:Nerve Fibers / Q000187:drug effects* / Q000502:physiology; D009475:Neurons, Afferent / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D011522:Protons; D051381:Rats; D017207:Rats, Sprague-Dawley; D019354:Sodium Lactate / Q000494:pharmacology*; D014630:Vagus Nerve / Q000166:cytology / Q000502:physiology
D005561:Formates; D006490:Hemostatics; D011522:Protons; C030544:formic acid; D019344:Lactic Acid; D006851:Hydrochloric Acid; D019354:Sodium Lactate