Day-night variations in blood and intracellular pH in a lizard,Dipsosaurus dorsalis

Summary

• 1. Blood pH,$P_{{\text{CO}}_2 }$ and$P_{O_2 }$ ofDipsosaurus dorsalis were measured during the day and at night. Lizards at constant body temperatures (25, 37°C) and lizards experiencing diurnal changes in body temperature similar to those in nature were studied.

• 2. In lizards at constant body temperatures, blood pH was about 0.1 unit less and blood$P_{{\text{CO}}_2 }$ was 4–7 Torr higher at night compared to day. Similar patterns were seen in lizards on natural thermal cycles (Figs. 1 and 2).

• 3. Intracellular pH (pH_i) of skeletal muscle, esophagus and liver was about 0.2 units lower at night than day but myocardial pH_i was unchanged (Table 1).

• 4. Reduction in breathing frequency, and thus a relative hypercapnia from hypoventilation was consistent with the nocturnal acidification of the blood and intracellular compartments (Fig. 3).

• 5. Nocturnal acidification (CO₂ retention) corresponds to periods of minimum metabolism. The possible impacts of diurnal shifts in hydrogen ion concentration on energy metabolism and metabolic regulation are discussed.