Ionic compensation with no renal response to chronic hypercapnia in Chrysemys picta bellii
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.