Journal of Neurophysiology, Vol 74, Issue 6 2707-2712, Copyright © 1995 by APS
Adaptation of carotid chemoreceptors to step increases in PaCO2 in anesthetized cats
R. A. Linton, D. M. Band and P. McLoughlin
Rayne Institute, St. Thomas's Hospital, London, United Kingdom.
1. The rate of change sensitivity of some carotid chemoreceptors to
within-breath changes in PaCO2 would suggest that the half-life of
adaptation of these receptors to a step increase is shorter than the 5-10 s
previously reported. 2. In six anesthetized cats, step increases in PaCO2
(10 in each cat) were produced by injection of CO2 into the inspired gas
during high-frequency jet ventilation. Chemoreceptor discharge was recorded
from single-fiber preparations of the divided carotid sinus nerve, and the
changes in PaCO2 were followed with the use of an in vivo pH electrode. 3.
The adaptation half-lives were 0.3, 0.8, 1.2, 1.3, 1.6, and 8.6 s. The
physiological significance of these findings in terms of respiratory
control and the mechanism of chemotransduction are discussed. The receptors
with the shortest and longest half-lives showed corresponding differences
in response to sine-wave oscillations in PaCO2. 4. In a further group of
five cats, chemoreceptor responses to step increases in PaCO2 were tested
before and during infusion of KCl to produce a mean arterial [K-] of 6.8
+/- 0.2 (SE) mM. Under these conditions the hyperkalemia caused no further
increase in discharge. 5. We conclude that adaptation of the chemoreceptor
response to increases in PaCO2 is much faster than previously reported and
that this finding is consistent with observations of chemoreceptor
responses to respiratory PaCO2 oscillations.
