Gunnar Lykkeboe

Respiratory adaptations in carp blood influences of hypoxia, red cell organic phosphates, divalent cations and CO2 on hemoglobin-oxygen affinity

SummaryThis study concerns the adaptation of oxygen transporting function of carp blood to environment hypoxia, tracing the roles played by erythrocytic cofactors, inorganic cations, carbon dioxide and hemoglobin multiplicity.Carp acclimated to hypoxia (

Respiratory properties of blood in awake and estivating lungfish, Protopterus amphibius☆

P_{O_2 }

Functional properties of hemoglobins in the teleostTilapia grahami

∼30 mmHg) display striking increases in blood oxygen affinity compared to normoxic (

Blood respiratory properties in the naked mole rat Heterocephalus glaber, a mammal of low body temperature☆

P_{O_2 }

Changes in the respiratory properties of the blood in the carp,Cyprinus carpio, induced by diurnal variation in ambient oxygen tension

=120–150 mm) specimens (P50s are 3.0 and 7.0 mm, respectively, at pH 7.9 and 20°C). This correlates with a marked decrease in erythrocytic concentrations of NTP (nucleoside triphosphates) (Figs. 1, 2, Table 1), permitting investigation of the time-course of the response (Fig. 3). That GTP (guanosine triphosphate) plays a greater role than ATP in the allosteric regulation of blood oxygen affinity, follows from greater decreases in its concentration during hypoxia, and its greater effect on oxygen affinity of the hemoglobin (Figs. 1, 5). It is furthermore shown that divalent cations (which complex with NTP) inhibit the regulatory role of GTP on O2 affinity to a lesser extent than that of ATP (Fig. 7). However, the divalent cation, Mg2+, occurs in similarly high concentrations in the erythrocytes of hypoxic and normoxic fish (Table 1). CO2 specifically depresses the O2 affinity of carp hemoglobin, but below pH 8.3, its effect is obliterated by ATP and GTP suggesting that the β chains are the main sites for CO2− binding. Four carp hemoglobin components are isolated and their oxygen-binding properties compared with those of the cofactor-free hemolysate (Figs. 4, 8, 9). The results are discussed comparatively with special reference to hemoglobin function in fish and mammals.

Effects of graded exercise on blood gas tensions and acid-base characteristics of rainbow trout

SummaryBlood respiratory properties of rainbow trout were determined following acclimation to normoxia and two levels of hypoxia.The most prominent response appeared to be an increase in blood O2 affinity graded to the level of hypoxia. TheP50 values (at pH 7.8 and 20°C) were 24.1 21.7 and 16.8 mm Hg when specimens were acclimated to water O2 tensions of 150, 80 and 50 mm Hg, respectively. The blood O2 affinity was closely correlated with the erythrocytic ATP concentration. The stepwise correlation of ATP andP50, when trout were exposed to graded oxygen lack in the water, indicates that the blood O2 affinity is precisely regulated.Anoxic incubation of trout blood in vitro induced a rapid reduction in erythrocytic ATP concentration (t1/2=75 min), which was closely correlated to theP50 value. The drop inP50 value during anoxic exposure can be explained partly by the direct allosteric effect of a decreased erythrocytic ATP concentration and partly by the modified Donnan distribution of protons across the red cell membrane. Reoxygenation of the incubated blood, however, only partly re-established the erythrocytic ATP concentration, with a concurrent rise inP50 value.The results invite discussion about the mechanism, by which fish regulate their blood O2 affinity. It is concluded, that it is regulated at the organismal rather than at the red cell level.