Gas exchnge in the lamprey, Entosphenus tridentatus

Abstract

1. 1. O 2-Hb dissociation curves of the lamprey, Entosphenus tridentatus, show a distinct sigmoid shape with an n-value of 1·88 and a Bohr factor of −0·41. Blood Hb concentration was 6·72 g % and O 2 capacity 9·15 vol. %. Blood buffering capacity was 3·5 mM/1/pH. 2. 2. E. tridentatus were able to maintain the O 2 uptake ( V ̇ O 2 ) at falling O 2 availability down to water O 2 tensions of 35–40 mm Hg at 20°C, and to 10 mm Hg at 5 and 15°C. Q 10 for V ̇ O 2 between 5 and 15°C averaged 1·6 and increased conspicuously to more than 6·0 from increased ventilatory activity and motor activity between 15 and 20°C. 3. 3. Heart rate and breathing rate changed with temperature in an exponential manner up till temperatures of 20°C which seemed to represent the upper tolerance limit. Dorsal aortic blood pressure showed mean values between 25 and 44 cm H 2O. Breathing rate rose markedly when water O 2 tension dropped below approximately 100 mm Hg. A reduced breathing rate accompanied breathing in hyperoxic water. Combination of progressive hypoxia and increasing temperature had a compounded effect on breathing rate. 4. 4. Arterial and venous PO 2 in blood sampled from free-swimming animals ranged between 58–77 mm Hg and 24–40 mm Hg respectively, corresponding to arterial saturations between 94 and 100 per cent. Venous O 2 saturation averaged 75 per cent. Percentage O 2 utilization in blood averaged 24·8 per cent. During activity both arterial and venous PO 2 dropped markedly but with a resultant increase in O 2 utilization due to the relative positions on the O 2-Hb dissociation curves. 5. 5. Hypoxia resulted in utilization of the large venous O 2 reservoir expressed by a three- to four-fold increase in O 2 utilization. The PO 2 gradient between the ambient water and blood diminished during hypoxia. 6. 6. Percentage O 2 extraction from the respiratory water current ranged between 10·0 and 24·8 per cent. The special mode of breathing in lampreys is discussed in relation to their exceptional tolerance to environmental stresses.