124
A.P.A. Wiihrmann
calcium in the optic tectum of Pleuragramma after cytochemical
precipitation of endogenous calcium. In contrast to other fish species in
the nerve cell membrane of Pleuragramma highly glycosylated
gangliosides are clustered at membraneous proteins, with the evidence of
a high Ca
2
+ accumulation within the synaptic cleft [20].
In summary, the results support the hypothesis that the concentration
and/or composition of neuronal gangliosides influence basic physicochemical properties of neuronal membranes. As a consequence, the
extremely high polarity of brain gangliosides of cold-blooded vertebrates,
especially of those living in habitats near the freezing point and the
polarization of the ganglioside composition may facilitate synaptic
transmission. Thus, the properties of gangliosides indicate a mechanism at
the molecular level that keeps the neuronal membranes functional, even
under the extreme temperature conditions of the Antarctic Ocean.
Antifreezes and Their Relation to the Mode of Life
In the high-Antarctic, shallow water species are abundant above 400-450
m depth. The benthic/epibenthic Cygnodraco mawsoni, Trematomus
pennellii and Pagetopsis macropterus are representatives of this group
and they possess high amounts of both low and high molecular weight
AFGP (Fig. 4). Eurybathic species are abundant over most of the depth
range down to 600-700 m. Pogonophryne scotti, Racovitzia glacialis,
Trematomus lepidorhinus and Cryodraco antarcticus belong to this group.
The antifreeze content among these fish is moderate, and lower in active
(c. antarcticus) than in sluggish species (P. scotti). Deeper shelf and
upper slope species occur only at depths below 400-450 m.
Lepidonotothen kempi, Dacodraco hunteri and Muraenolepis marmoratus
in the Lazarev Sea, Bathydraco marri and Trematomus loennbergi in the
Weddell Sea are examples of this group. The Lazarev Sea species have
lower amounts of antifreezes which is likely related to the higher water
temperature [21].
While antifreeze protection down to -2.2 °C is necessary for fishes
inhabiting relatively shallow ice-laden water, most nonnotothenioid
species and some notothenioids (e.g. Neopagetopsis ionah) live at 600 m
depth and deeper, a habitat with different physical parameters and less ice.
Seawater at the surface of the Weddell Sea freezes at approx. -1.86 0c.
Because of the pressure effect on the freezing point (0.00753 °C 10 m-\
[22]), seawater at 500 m depth with a salinity of 34.7%0 freezes in situ at
-2.24°C. Hence, based on the freezing point of serum, the freezing point
A.P.A. Wiihrmann
calcium in the optic tectum of Pleuragramma after cytochemical
precipitation of endogenous calcium. In contrast to other fish species in
the nerve cell membrane of Pleuragramma highly glycosylated
gangliosides are clustered at membraneous proteins, with the evidence of
a high Ca
2
+ accumulation within the synaptic cleft [20].
In summary, the results support the hypothesis that the concentration
and/or composition of neuronal gangliosides influence basic physicochemical properties of neuronal membranes. As a consequence, the
extremely high polarity of brain gangliosides of cold-blooded vertebrates,
especially of those living in habitats near the freezing point and the
polarization of the ganglioside composition may facilitate synaptic
transmission. Thus, the properties of gangliosides indicate a mechanism at
the molecular level that keeps the neuronal membranes functional, even
under the extreme temperature conditions of the Antarctic Ocean.
Antifreezes and Their Relation to the Mode of Life
In the high-Antarctic, shallow water species are abundant above 400-450
m depth. The benthic/epibenthic Cygnodraco mawsoni, Trematomus
pennellii and Pagetopsis macropterus are representatives of this group
and they possess high amounts of both low and high molecular weight
AFGP (Fig. 4). Eurybathic species are abundant over most of the depth
range down to 600-700 m. Pogonophryne scotti, Racovitzia glacialis,
Trematomus lepidorhinus and Cryodraco antarcticus belong to this group.
The antifreeze content among these fish is moderate, and lower in active
(c. antarcticus) than in sluggish species (P. scotti). Deeper shelf and
upper slope species occur only at depths below 400-450 m.
Lepidonotothen kempi, Dacodraco hunteri and Muraenolepis marmoratus
in the Lazarev Sea, Bathydraco marri and Trematomus loennbergi in the
Weddell Sea are examples of this group. The Lazarev Sea species have
lower amounts of antifreezes which is likely related to the higher water
temperature [21].
While antifreeze protection down to -2.2 °C is necessary for fishes
inhabiting relatively shallow ice-laden water, most nonnotothenioid
species and some notothenioids (e.g. Neopagetopsis ionah) live at 600 m
depth and deeper, a habitat with different physical parameters and less ice.
Seawater at the surface of the Weddell Sea freezes at approx. -1.86 0c.
Because of the pressure effect on the freezing point (0.00753 °C 10 m-\
[22]), seawater at 500 m depth with a salinity of 34.7%0 freezes in situ at
-2.24°C. Hence, based on the freezing point of serum, the freezing point