Channels and pumps—determinants of metabolic cold adaptation strategies

Abstract

1. 1. In all cells the passive diffusion of ions through transmembrane channels must be precisely balanced by the active transport of ions against concentration gradients, i.e., the ratio of ion channel/ion pump fluxes must be controlled at unity. 2. 2. One reason why some cells are cold sensitive is because temperature differentially affects these two processes and the necessary balance between them breaks down. 3. 3. Polar fishes apparently maintain channel/pump flux ratios at unity by upward adjustments in functional pump densities. 4. 4. That is presumably why their maintenance metabolic requirements are higher, which is an important cause of their higher-than-expected metabolic rates. This is the causal basis for the paradigm of metabolic cold adaptation in polar fishes. 5. 5. Channel/pump flux ratios of unity in principle also could be achieved in cold tolerant organisms by downward adjustments in functional channel densities of cell (and organelle) membranes. 6. 6. However, organisms utilizing this strategy would be expected to display profoundly reduced metabolic rates, reduced scopes for activity, and reduced osmoregulatory capacities. 7. 7. Deep sea fishes, also normally functional at low temperatures, display drastically reduced metabolic rates compared to other fishes and may well illustrate the latter strategy.