274
D. J. RANDALL
1966; Lenfant et al., 1966-1967; Garey, 1967; Griggs, 1967; Hunn, 1967;
Johansen et al., 1966; Johansen and Lenfant, 1987; Yiipcr and Baumgarten-Schumann, 196%).
Recently, Forstcr and Steen (1969) have mcasured the half-time for
some oxygcn hemoglobin reactions in the blood of eels, but apart from
these data very little is known about oxygen hemoglobin reaction times
and these may play a role in limiting thc rate of gas exchange across the
gills. In telcost fish an increase in CO, content or a decrease in p H of the
blood causes not only a reduction in the affinity of hemoglobin for
oxygen (Bohr effect ) but also a reduction in the oxygen carrying capacity
of the blood (Root effect). Unlike the blood of terrestrial mammals, teleost
hemoglobin never becomes fully saturated once the Pcol is more than
1-2 mm Hg (Fig. 7). The magnitude of this “Root effect” is largest at
C 0 2 tensions between 1 and 5 nim Hg and decreases with an increase
in PCo2 above this range. If the CO, tension in blood fully saturated with
oxygen is increased, oxygen is released from the hemoglobin (Root-off
shift), and if the CO, tension is lowercd the reverse occurs (Root-on shift).
The half-time for the eel Hoot-off shift at 23”-25”C, produccd by an
increase in P.,,, is 87 msec, whereas the half-time for the reverse Hooton shift is 9 sec (Forster and Steen, 1969). Tlie asymmctrical reaction
velocities of the Root shift are important in unloading gases in the
swim bladder (Berg and Stecn, 1968), but a slow Root-on shift will
impair oxygen transfer across the gills. The time course of the Root-on
shift is related to the reaction velocity of the uncatalyzed C 0 2 hydrationdehydration reaction in the plasma. The presence of a CO, sink, for
example, water passing ovcr the gills, will cause a more rapid reduction
of plasma and intracellular Pco2 than recorded under the conditions of
Forster and Steen’s experiments, and hence thc rate of the Root-on
shift will be more rapid as blood passes through the gills. Blood
leaving the gills is usually 95% saturated with oxygen in trout (Stevcns
and Randall, 1967b). Incomplete saturation of arterial blood has been
recorded in the eel (Steen and Kruyssc, 1964) but this was probably
related to the utilization of vcnous shunts in the gills rather than the
result of a slow Root-on shift.
Acclimation to high CO, levels in the watcr has been reported to
depress the magnitude of Root effect (Eddy and Morgan, 1969). This
acclimation process is associated with an increase in hernoglobin levels
with little change in blood oxygen capacity. These obscwations require
further investigation.
Teleosts generally have a marked Bohr and Root effect, both of
which are absent or small in elasniobranchs (Lcnfant and Johansen,
1966). There is no Root effect in Dipnoi, but there is a pronounced Bohr
D. J. RANDALL
1966; Lenfant et al., 1966-1967; Garey, 1967; Griggs, 1967; Hunn, 1967;
Johansen et al., 1966; Johansen and Lenfant, 1987; Yiipcr and Baumgarten-Schumann, 196%).
Recently, Forstcr and Steen (1969) have mcasured the half-time for
some oxygcn hemoglobin reactions in the blood of eels, but apart from
these data very little is known about oxygen hemoglobin reaction times
and these may play a role in limiting thc rate of gas exchange across the
gills. In telcost fish an increase in CO, content or a decrease in p H of the
blood causes not only a reduction in the affinity of hemoglobin for
oxygen (Bohr effect ) but also a reduction in the oxygen carrying capacity
of the blood (Root effect). Unlike the blood of terrestrial mammals, teleost
hemoglobin never becomes fully saturated once the Pcol is more than
1-2 mm Hg (Fig. 7). The magnitude of this “Root effect” is largest at
C 0 2 tensions between 1 and 5 nim Hg and decreases with an increase
in PCo2 above this range. If the CO, tension in blood fully saturated with
oxygen is increased, oxygen is released from the hemoglobin (Root-off
shift), and if the CO, tension is lowercd the reverse occurs (Root-on shift).
The half-time for the eel Hoot-off shift at 23”-25”C, produccd by an
increase in P.,,, is 87 msec, whereas the half-time for the reverse Hooton shift is 9 sec (Forster and Steen, 1969). Tlie asymmctrical reaction
velocities of the Root shift are important in unloading gases in the
swim bladder (Berg and Stecn, 1968), but a slow Root-on shift will
impair oxygen transfer across the gills. The time course of the Root-on
shift is related to the reaction velocity of the uncatalyzed C 0 2 hydrationdehydration reaction in the plasma. The presence of a CO, sink, for
example, water passing ovcr the gills, will cause a more rapid reduction
of plasma and intracellular Pco2 than recorded under the conditions of
Forster and Steen’s experiments, and hence thc rate of the Root-on
shift will be more rapid as blood passes through the gills. Blood
leaving the gills is usually 95% saturated with oxygen in trout (Stevcns
and Randall, 1967b). Incomplete saturation of arterial blood has been
recorded in the eel (Steen and Kruyssc, 1964) but this was probably
related to the utilization of vcnous shunts in the gills rather than the
result of a slow Root-on shift.
Acclimation to high CO, levels in the watcr has been reported to
depress the magnitude of Root effect (Eddy and Morgan, 1969). This
acclimation process is associated with an increase in hernoglobin levels
with little change in blood oxygen capacity. These obscwations require
further investigation.
Teleosts generally have a marked Bohr and Root effect, both of
which are absent or small in elasniobranchs (Lcnfant and Johansen,
1966). There is no Root effect in Dipnoi, but there is a pronounced Bohr