Ion and Metabolite Transport Through the Intestinal Membranes of I bernacchii
245
mucosa of the Antarctic fish possess a much higher amount of MUF A with
respect to that of the European eel [4]. Temperature dependence (Fig. 4) of
N a + -D-glucose cotransporter of T. bernacchii intestine is not only
completely different from that of eel intestinal sugar transporter but also
different from those previously reported for other functionally extrinsic
enzymatic proteins such as alkaline phosphatase and leucine
aminopeptidase of the same Antarctic species [2]. An exponential increase
of activity with temperature has also been found for the intestinal Na + JK+ATPase (Fig. 5) similar to that previously reported in kidney of T.
bernacchii [17]. However both these experimental observations concern
only the effects of temperatures on ATP-hydrolysis catalysed by Na+JK+ATPase while no information is at the moment available on the ion
transport capacity mediated by this active pump at different temperatures.
In light of these considerations, the most important characteristics of the
Na+-D-glucose transport activity of T. bernacchii intestine are the
quantification of the true substrate transport and the inactivation
temperature limit (that intriguingly corresponds to that lethal for these
animals). A protein unfolding, but more likely a modification of lipidprotein interaction forces, could be possible explanations of this
temperature effect. In this regard T. bernacchii intestinal brush border
membranes have an amount of poly- and monounsaturated fatty acids,
significantly higher than that reported for the European eel (Acierno et al.
unpublished data), in accordance with the phenomenon of homeoviscus
adaptation, characteristic of cold-acclimated poikilotherms [18]. In
principle this phenomenon, significantly influencing the physical state of
the membrane by increasing its fluidity at low temperatures, could induce,
at temperatures higher than those of T. bernacchii environment, a lipidprotein disassembling leading to a negative effect on functionality of
intrinsic proteins such as Na+-D-glucose cotransporter. However, also if
influences of lipid modification on transport protein activity were
previously observed [19], other studies are needed to better clarify this
aspect.
References
1. Eastman JT (1993) Antarctic fish biology. Academic Press, San Diego
2. Maffia M, Acierno R, De Ceglie G, Vilella S, Storelli C (1993) Adaptation of
intestinal cell membrane enzymes to low temperatures in the Antarctic teleost
Pagothenia bernacchii. J Comp Physiol BI63:265-270
3. Maffia M, Acierno R, Cillo E, Storelli C (1996) Na+-D-glucose cotransport
by intestinal BBMV s of the Antarctic fish Trematomus bernacchii. Am J
Physiol271:R1576-RI583
4. Acierno R, Maffia M, Sicuro P, Fiammata L, Rollo M, Ronzini L, Storelli C
(1996) Lipid and fatty acid composition of intestinal mucosa of two Antarctic
245
mucosa of the Antarctic fish possess a much higher amount of MUF A with
respect to that of the European eel [4]. Temperature dependence (Fig. 4) of
N a + -D-glucose cotransporter of T. bernacchii intestine is not only
completely different from that of eel intestinal sugar transporter but also
different from those previously reported for other functionally extrinsic
enzymatic proteins such as alkaline phosphatase and leucine
aminopeptidase of the same Antarctic species [2]. An exponential increase
of activity with temperature has also been found for the intestinal Na + JK+ATPase (Fig. 5) similar to that previously reported in kidney of T.
bernacchii [17]. However both these experimental observations concern
only the effects of temperatures on ATP-hydrolysis catalysed by Na+JK+ATPase while no information is at the moment available on the ion
transport capacity mediated by this active pump at different temperatures.
In light of these considerations, the most important characteristics of the
Na+-D-glucose transport activity of T. bernacchii intestine are the
quantification of the true substrate transport and the inactivation
temperature limit (that intriguingly corresponds to that lethal for these
animals). A protein unfolding, but more likely a modification of lipidprotein interaction forces, could be possible explanations of this
temperature effect. In this regard T. bernacchii intestinal brush border
membranes have an amount of poly- and monounsaturated fatty acids,
significantly higher than that reported for the European eel (Acierno et al.
unpublished data), in accordance with the phenomenon of homeoviscus
adaptation, characteristic of cold-acclimated poikilotherms [18]. In
principle this phenomenon, significantly influencing the physical state of
the membrane by increasing its fluidity at low temperatures, could induce,
at temperatures higher than those of T. bernacchii environment, a lipidprotein disassembling leading to a negative effect on functionality of
intrinsic proteins such as Na+-D-glucose cotransporter. However, also if
influences of lipid modification on transport protein activity were
previously observed [19], other studies are needed to better clarify this
aspect.
References
1. Eastman JT (1993) Antarctic fish biology. Academic Press, San Diego
2. Maffia M, Acierno R, De Ceglie G, Vilella S, Storelli C (1993) Adaptation of
intestinal cell membrane enzymes to low temperatures in the Antarctic teleost
Pagothenia bernacchii. J Comp Physiol BI63:265-270
3. Maffia M, Acierno R, Cillo E, Storelli C (1996) Na+-D-glucose cotransport
by intestinal BBMV s of the Antarctic fish Trematomus bernacchii. Am J
Physiol271:R1576-RI583
4. Acierno R, Maffia M, Sicuro P, Fiammata L, Rollo M, Ronzini L, Storelli C
(1996) Lipid and fatty acid composition of intestinal mucosa of two Antarctic