John S. Willis

>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.

Since leaving the lab I have devoted myself, scientifically, to exploring databases and 3-D molecular models available online trying to shed light on unresolved issues arising from my published work. Most recently, in my 90^th year, I have returned to a phenomenon that I published on more than 60 years ago (Marshall & Willis, J. Physiol. 164:64, 1962), the persistence and actual enhancement of the action potential at 6ºC in atria of ground squirrels, a hibernator. (AP is blocked in atria of guinea pig and rabbit at that temperature.) My interest in this was reawakened by a genomic study of mammals (Christmas, et al., Science 380:eabn3943, 2023) that showed that the gene SCN2A, coding for the voltage gated Na channel in brain and heart, is one showing “rapid evolution” (i.e., greater deviation) in species that hibernate.