AJP - Regulatory, Integrative and Comparative Physiology, Vol 245, Issue 5 689-R694, Copyright © 1983 by American Physiological Society
Acid-base and ionic balance in Ambystoma tigrinum and Necturus maculosus during hypercapnia
D. F. Stiffler, B. L. Tufts and D. P. Toews
The aquatic urodeles Ambystoma tigrinum and Necturus maculosus responded to
hypercapnia quite differently. A. tigrinum, after 2-h exposure to 22 Torr
partial pressure of CO2 (PCO2), decreased arterial pH (pHa) from 7.85 to
7.32 and increased arterial pressure of CO2 (PaCO2) to 26 Torr. Plasma
[HCO-3] [( HCO-3]pl) remained constant at about 17 mM. Prolonged exposure
(24 h) led to a 26% extracellular compensation as pHa rose to 7.46 while
[HCO-3]pl increased to 24 mM. Plasma [K+] increased and [Cl-] decreased
while [Na+] remained unchanged. Recovery in normocapnic water reversed
these changes. N. maculosus did not display similar compensatory changes.
Two-hour exposure to 17 Torr PCO2 resulted in a decline of pHa from 7.66 to
7.24, which was not compensated (pHa = 7.19) after 24 h. There were no
significant changes in plasma [Na+], [K+], [Cl-], or [HCO-3]. The pHa
decline reversed after recovery in normocapnic water, however. The fact
that compensation for hypercapnic in A. tigrinum was accompanied by changes
in Cl- and K+ concentrations may indicate the participation of epithelial
transport mechanisms involving these ions in acid-base balance.
