AJP - Regulatory, Integrative and Comparative Physiology, Vol 251, Issue 6 1228-R1234, Copyright © 1986 by American Physiological Society
Ionic compensation with no renal response to chronic hypercapnia in chrysemys picta bellii
R. B. Silver and D. C. Jackson
The ionic compensatory response to CO2 breathing for 3 days was studied on
intact and cystectomized turtles at 10 and 20 degrees C. Arterial blood
gases, pH, ionized calcium, and the plasma concentrations of Na+, K+, Cl-,
total Ca2+, and total Mg2+ were measured periodically. At 20 degrees C,
ureteral urine was also collected from bladderless turtles and was analyzed
for pH, ions, NH3+, total CO2, osmolality, and titratable acid. When CO2
was breathed there was a compensatory change in the strong-ion difference
as manifest by an increase in plasma [HCO3-] that was approximately 10
meq/l both in the 10 and 20 degrees C turtles. The only significant
associated strong-ion changes observed consistent with the ionic
compensatory response were increases in total and ionized Ca2+ and total
Mg2+. These results were unaffected at either temperature by surgical
removal of the urinary bladder. Urine collected from cystectomized turtles
showed no compensatory increase in acid excretion during hypercapnia; in
fact, changes occurred in the opposite direction. Urinary excretion of
HCO3- and urine pH increased significantly, whereas titratable acidity
decreased significantly. No significant change occurred in ammonia
excretion over the three days of hypercapnia. These data argue against
compensatory roles for the kidneys and urinary bladder in this species and
point to internal ionic exchanges involving bone and shell.
