As well as the generality of enzymatic processes of poikilotherms, transport phenomena through cell membranes are impaired by low environmental temperatures. In particular low temperature can not only directly affect protein stability and functionality but, also, the functionality of the lipid microenvironment on which transporters are embedded or linked. As a consequence low temperature represents a major challenge in ionic and metabolic regulation of ectothermic organisms. Although the impairing effect of low temperatures influences all kind of transport phenomena, passive routes are less influenced by low temperatures than active transporters or, in other words diffusional pathways are less temperature sensitive than transport mediated processes. In this light, the adaptation of membrane transport processes represents a common component of a wide range of physiological and adaptive reactions of ectothermic organisms to cold, like hibernation, freeze avoidance, membrane functionality preservation, protein stability, etc. While a conspicuous amount of data on enzyme adaptation to low temperatures is to date available, very little is known on the effect of cold on membrane transports in polar fish and, in particular on those transporters that are involved in ion and metabolic homeostasis at cellular level.
In this paper we describe the results obtained in the recent years from the study of cell membrane transporters of polar fish, in particular Antarctic teleost. The characterisation of plasma membrane transports of macromolecules and ions and the identification of plasma membrane lipid are reported. The known molecular mechanisms which allow polar teleost to keep the functionality of the membrane bilayer ion channels and carrier proteins at a level compatible with the maintenance of the basic homeostatic processes are illustrated. Research perspectives and possibilities are discussed.
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