>A central paradigm in animal cell physiology is that long-term regulation of cell volume consists of a balance between the metabolically dependent activity of the Na-K pump ("Na-K ATPase") and the inward leakage of Na and outward leakage of K. The ion gradients that this balance maintains also establish the membrane potential of excitable cells and provide an energy source for uphill transport of organic molecules. My interest in this paradigm has centered on its maintenance or failure at low and high temperatures. For many years I used its maintenance in cells of cold-resistant mammalian hibernators at temperatures near zero degrees centigrade as a contrast to its failure in more typical mammalian cells. In part this difference depends on the continued effective operation of the Na-K pump in cold resistant cells. We found that loss of ability of the pump in intact, cold-sensitive cells to utilize ATP at low temperature accounted for much of the failure. However, this difference in ATP affinity is lost in cell-free ATPase and examination of amino acid sequences of pumps of the two types did not reveal any obvious causes of the difference.
The other leg of the balance and therefore the other candidate for consideration is passive permeation, but this is a harder steer to lasso, because there are many pathways and the specific complement varies among different cell types. Working at elevated temperatures with guinea pig red cells we found that activation of a K-Cl cotransport pathway could balance the excessive gain of K due to faster operation of the Na-K ATP pump as cells are warmed above their normal range. The mechanisms of coordination of such changes in the face of thermal or other environmental challenges among the various pathways present and between them as a group and the Na-K pump, however, remain an open topic for study.
My current scientific interests revolve around the use and misuse of the Arrhenius equation and Boltzmann kinetics to account for effects of temperature on complex systems and around possible alternatives to the Na-pump-leak paradigm in animal cells.
Membrane transport mechanisms, responses to changes of temperature and metabolic state
Willis, J. S and Milanick, M.A. (2005). Implications of SERCA structural models for ATP binding events in Na,K-ATPase ("NaKA"). J. Gen. Physiol. 126:15.
Willis, J. S. (2004) "The Balancing Act of the Naked Cell" in Cell Volume Regulation, P. K. Lauf and N.Adragna, eds. Springer, pp. 1-9.
Willis, J. S. and Anderson, G. L. (1998) Activation of K Cl cotransport by mild warming in guinea pig red cells. J. Membrane Biol. 163:193 203.
Marjanovic, M. and Willis, J. S. (1992) ATP dependence of Na K pump of cold sensitive and cold tolerant mammalian red blood cells. J. Physiol. (Lond.) 456:575 590.