Respiratory and cardiovascular physiology of the aquatic snake,Acrochordus arafurae

Summary

• 1. This study examines O₂ and CO₂ exchange and transport, energy production and the biochemical properties of blood and muscle in a sluggish aquatic snake.

• 2. The hemoglobin (Hb) concentration and hematocrit were low compared to other reptiles (Table 1) but the buffer capacity was higher (Tables 1,2). Hb-O₂ equilibrium curves of whole blood showed high affinity, high Bohr effect, low cooperativity and low temperature sensitivity (Tables 1,3; Figs. 2–4). ATP was the major organic modifier of the Hb; there was no 2,3 DPG (Fig. 1, Table 1).

• 3. Low myoglobin concentration and relatively high O₂ saturation in the pulmonary artery (Table 5) imply low rates of O₂ uptake by the tissues, even during activity.

• 4. The high Hb−O₂ affinity favors replenishment of blood O₂ stores but does not limit O₂ delivery to those tissues of low O₂ requirements. Where regional differences in O₂ demands occur, the large Bohr effect compensates for high affinity by releasing more O₂ at higher$P_{O_2 }$ in active tissues.

• 5. Low specific activities of selected glycolytic enzymes from skeletal muscle (Table 4) and the characteristics of lactate dehydrogenase pointed to low capacities for aerobic and anaerobic energy production, confirmed by measurements of O₂ uptake and lactate production during forced activity. Fatigue occurred despite high circulating O₂ reserves (Fig. 9) and blood lactate levels characteristic of other snakes at rest (Table 2).

• 6. During voluntary apnea, O₂ is recruited at variable rates from the lung and both sides of the circulatory system. CO₂ exchange in the lung quickly ceases and often reverses (Figs. 5,7,8). Much of the CO₂ stored in the blood and tissues during the dive enters the lung during the ventilatory episodes consisting of several breaths. Pulmonary blood flow increases during ventilation (Figs. 5–7) and the duration of the episode ensures that almost the entire blood volume passes through the lung.