10. THE SWIM BLADDER AS A HYDROSTATIC ORGAN
437
gradient is not based on impermeability of the rete to acid but instead
on the slow response of the 0, capacity of blood to decreasing H+ ion
concentration. The slow Root on-shift thus explains how the rete can
work in spite of the fact that it is permeable to acid.
The rate constants hereby introduced into the system will also make
the system dependent upon blood flow in another and biologically more
attractive manner than previously assumed. The Kuhn model implies
that at a low flow rate the extraction of 0, from the blood is maximum.
Introduction of rate constants indicates that when the flow is low the
arteriovenous acid flux will have sufficient time to influence the arteriovenous Po, gradient and thus reduce the degree of extraction. It is thus
quite possible to circulate a bladder at a low perfusion rate without
significant deposition of 0,. The full consequence of these kinetic
parameters will be evident only when incorporated into a mathematical
model of the countercurrent multiplying system.
It was shown by Fange ( 1953) that acetozolamide (Diamox), which
inhibits the catalytic action of carbonic anhydrase on the reaction of
H,O with CO,, will abolish gas deposition. In a recent investigation,
Forster and Steen (1969) showed that this inhibitor lengthened the
half-time of the Root off-shift from a normal value of 50 msec at 20°C
to at least 30 sec. It is very likely that this explains Fange’s observation.
The acid secreted by the bladder epithelium would act too slowly to
cause significant 0, release from the blood during the period of time
it circulates in the swim bladder.
The model for inert gas concentrations based on salting out effect
(Kuhn and Kuhn, 1961) should also take into account the diffusion constants of inert gases relative to that of water and ions. The half-time
for water penetration of eel red cells during osmotic swelling has been
measured by Blum (personal communication) to be 2-3 min, as compared to less than 20 msec for 0, diffusion out of the red cell (Forster and
Steen, 1969). N2 will diffuse through water roughly at half the speed of
0, and is thus apparently so much faster than H,O diffusion that countercurrent multiplication of inert gases via the salting out effect can take
place.
CONCLUSION
At present it seems feasible to explain the concentration of 0, and
of inert gases in fishes with a rete by countercurrent multiplication of a
primary effect caused by lactic acid. Other ions, yet unidentified, may
possibly be involved.
437
gradient is not based on impermeability of the rete to acid but instead
on the slow response of the 0, capacity of blood to decreasing H+ ion
concentration. The slow Root on-shift thus explains how the rete can
work in spite of the fact that it is permeable to acid.
The rate constants hereby introduced into the system will also make
the system dependent upon blood flow in another and biologically more
attractive manner than previously assumed. The Kuhn model implies
that at a low flow rate the extraction of 0, from the blood is maximum.
Introduction of rate constants indicates that when the flow is low the
arteriovenous acid flux will have sufficient time to influence the arteriovenous Po, gradient and thus reduce the degree of extraction. It is thus
quite possible to circulate a bladder at a low perfusion rate without
significant deposition of 0,. The full consequence of these kinetic
parameters will be evident only when incorporated into a mathematical
model of the countercurrent multiplying system.
It was shown by Fange ( 1953) that acetozolamide (Diamox), which
inhibits the catalytic action of carbonic anhydrase on the reaction of
H,O with CO,, will abolish gas deposition. In a recent investigation,
Forster and Steen (1969) showed that this inhibitor lengthened the
half-time of the Root off-shift from a normal value of 50 msec at 20°C
to at least 30 sec. It is very likely that this explains Fange’s observation.
The acid secreted by the bladder epithelium would act too slowly to
cause significant 0, release from the blood during the period of time
it circulates in the swim bladder.
The model for inert gas concentrations based on salting out effect
(Kuhn and Kuhn, 1961) should also take into account the diffusion constants of inert gases relative to that of water and ions. The half-time
for water penetration of eel red cells during osmotic swelling has been
measured by Blum (personal communication) to be 2-3 min, as compared to less than 20 msec for 0, diffusion out of the red cell (Forster and
Steen, 1969). N2 will diffuse through water roughly at half the speed of
0, and is thus apparently so much faster than H,O diffusion that countercurrent multiplication of inert gases via the salting out effect can take
place.
CONCLUSION
At present it seems feasible to explain the concentration of 0, and
of inert gases in fishes with a rete by countercurrent multiplication of a
primary effect caused by lactic acid. Other ions, yet unidentified, may
possibly be involved.