Ventilatory and Acid-Base Responses to Long-Term Hypercapnia in the Freshwater Turtle, Chrysemys Picta Bellii Available to Purchase

The response to hypercapnia was studied in western painted turtles, Chrysemys picta bellii at 20°C. Ventilation, metabolic rate, arterial blood gases, blood pH and blood plasma ions were monitored periodically on individual turtles exposed to 5·7% CO₂ for 72 h and then allowed to recover in air.

In response to hypercapnia, there is an immediate 10-to 15-fold increase in ventilation from control levels, which was maintained throughout the entire 5·7% CO₂ breathing period. The first hour of CO₂ breathing caused an increase in from 24–39 mmHg with a concomitant decrease in pH and rise in [HCO₃⁻]. [HCO₃⁻] rose from 42 to 50 mmol l⁻¹ in the next 24 h of CO₂ breathing and remained at this level for the rest of the hypercapnic period. Small, significant increases in total [Ca²⁺] and total [Mg²⁺] were found; however, no changes were observed in the plasma Na⁺, K⁺ or Cl⁻ concentrations and the overall change in measured ions could not account for the increased [HCO₃⁻]. The maximum change in [HCO₃⁻] attained in Chrysemys exposed to a more severe acidosis (14·3% CO₂) for up to 18 h was the same as that seen in the animals breathing 5·7% CO₂ (10 mmol l⁻¹) implying that there is an upper limit for the accumulation of [HCO₃⁻] in Chrysemys at 20 °C.

The blood pH of turtles recovering in air returned to the control value (7⁻56–7’74) within the first hour although did not return to the control value. The HCO₃⁻ ion concentration also remained elevated throughout the 48-h recovery period, which suggests that ionic compensation is a slower process.

The freshwater turtle employs two mechanisms to reduce the severity of an imposed respiratory acidosis: increased ventilation and changes in the strong ion difference. In spite of these responses, blood pH is not restored to the control value.