Newsgroup: it.scienza.biologia
Titolo: Pesci senza emoglobina

Salve!
Recentemente ho visto in televisione una puntata di "Ulisse" con Alberto
Angela
In questa trasmisione si č parlato di pesci e dell' antartide.
Mi ha colpito il fatto che in antartide esistono dei pesci nel cui sangue
non si trova
emoglobina; perchč diversamente questo si congelerebbe....
Come si chiamano questi pesci?
come fanno a respirare se nel loro sangue non c'č emoglobina?
Saluti a tutta la lista
Michele

 come fanno a respirare se nel loro sangue non c'è emoglobina?
AFAIK infatti non funziona cosi'. nel sangue dei pesci c'e' una sostanza 
antigelo (etilen glycol) che previene il congelamento del sangue. 
Varianti di emoglobina sono presenti in tutti i vertebrati necessariamente
-- 
nei campi di neve
verdissimo il verde
delle erbe nuove

 Varianti di emoglobina sono presenti in tutti i vertebrati necessariamente
No, no. I Channichthyidae (questo il nome della famiglia) sono proprio
privi di emoglobina. Il fatto di vivere in acque molto fredde penso li
aiuti, perché la solubilità dell'ossigeno (come della maggior parte dei
gas) nel plasma, aumenta al diminuire della temperatura.
-- 
Fabrizio

 come fanno a respirare se nel loro sangue non c'è emoglobina?
http://www.asgsb.org/bulletins/v13n2/vol13n2p25-34.pdf
"All channichthyid icefishes share the remarkable
characteristic of lacking hemoglobin and red cells in their
circulation. We have learned recently that this state is the result of
an apparently complete deletion of the gene for b-globin and partial
loss of the gene for a-globin (Cocca et al. 1995). Channichthyid
icefishes are the only known vertebrate animals to display this
attribute as adults, and they have received considerable attention
from comparative biologists interested in determining how adequate
oxygenation of tissues can be accomplished in the absence of a
circulating oxygen-binding protein.
Several fairly draconian modifications of the cardio-vascular
system of icefishes may help compensate for the lack of a
circulating oxygen-carrier:
 - Icefishes possess very large hearts compared to
red-blooded fishes of equivalent body size, and large
heart size results in a weight-specific cardiac output
that is four- to five-fold greater than that of redblooded
species (Hemmingsen et al., 1972)
 -  The blood volumes of icefishes are up to four-fold
those of red-blooded teleosts, and the diameter of their
capillaries is unusually large (Fitch et al., 1984)
This combination of cardiovascular features permits a large volume
of blood to circulate throughout the bodies of icefishes at a high
flow rate. Yet, because of decreased peripheral resistance, vascular
pressure is relatively low. Combined with the very high oxygen
content of Antarctic waters and the relatively low absolute
metabolic rate of these animals, alluded to above,
these circulatory features apparently ensure delivery of sufficient
oxygen to tissues (Hemmingsen, 1991). These traits are most likely
adaptive, in the sense that they at least partially compensate for
the lack of hemoglobin in the circulation of these animals.
Can loss of hemoglobin expression itself be considered an
adaptive feature in icefishes? I suspect not, even though a
consensus answer to this question has not emerged. Despite
arguments made by some about the benefits of the lowered blood
viscosity and cardiac work that accompany loss of red cells,
reduction in blood oxygen-carrying capacity to <10% that of
hemoglobin-expressing fishes would seem to more than offset this
advantage. As Eastman (1993) pointed out, the very existence of
rather remarkable features of cardiovascular anatomy and
physiology (heart size, capillary diameter, etc.) that appear to have
been selected to compensate for loss of a circulating oxygen-carrier
testifies that mutation(s) leading to this loss probably had
deleterious consequences."
-- 
Fabrizio