Acid-base and ionic balance in Ambystoma tigrinum and Necturus maculosus during hypercapnia.
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.
D000136:Acid-Base Equilibrium; D000557:Ambystoma / Q000502:physiology*; D000818:Animals; D001639:Bicarbonates / Q000097:blood; D002245:Carbon Dioxide / Q000097:blood; D002712:Chlorides / Q000097:blood; D004573:Electrolytes / Q000097:blood*; D006863:Hydrogen-Ion Concentration; D006935:Hypercapnia / Q000503:physiopathology*; D009337:Necturus / Q000502:physiology*; D010313:Partial Pressure; D011188:Potassium / Q000097:blood; D012964:Sodium / Q000097:blood; D013045:Species Specificity
D001639:Bicarbonates; D002712:Chlorides; D004573:Electrolytes; D002245:Carbon Dioxide; D012964:Sodium; D011188:Potassium