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Stimulation of pulmonary C fibres by lactic acid in rats: contributions of H+ and lactate ions.
Author(s) -
Hong J L,
Kwong K,
Lee L Y
Publication year - 1997
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1997.sp022023
Subject(s) - lactic acid , chemistry , formic acid , stimulation , medicine , biophysics , biochemistry , endocrinology , biology , bacteria , genetics
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.