Ventilatory frequency and haemolymph acid-base status during short-term hypercapnia in the locust, Schistocerca nitens

In this study, I investigated the role of the locust ventilatory system in haemolymph acid-base regulation during short-term (50 min) exposure to elevated environmental carbon dioxide. In American locusts, Schistocerca nitens, abdominal pumping frequency increased linearly with inspired P_CO2 (P₁CO₂) to a P₁CO₂ of 107 mmHg (1 mmHg = 133.3 Pascals). Ventilatory frequency was strongly correlated with haemolymph acid-base variables, consistent with the hypothesis that changes in ventilatory frequency were caused by changes in haemolymph pH or P_CO2. As inspired P_CO2 increased, the partial pressure gradient for carbon dioxide from haemolymph to air decreased, reducing the changes in haemolymph pH. Slopes of in vivo and in vitro buffer lines were statistically indistinguishable, suggesting that changes in haemolymph pH in vivo were due primarily to changes in haemolymph P_CO2. The results of this study indicate that the locust ventilatory system plays the dominant role in limitation of changes in haemolymph pH during short-term hypercapnia.