Evidence implicating a membrane ATPase in the control of passive permeability of excitable cells

The temperature sensitivity of the ATPase enzyme systems in a muscle microsomal preparation from the crayfish, Astacus pallipes , was studied. Preincubation of the enzyme preparation in the range 33–36°C produced a marked inactivation of the ATPases; the Mg ++ ‐dependent ATPase was very much more sensitive to this treatment than the Na + ‐K + ‐Mg ++ ‐dependent ATPase. Thus, the Arrhenius μ for the inactivation of the Mg ++ ‐dependent ATPase produced by eight minute preincubation is > 100 Kcals. These results are compared with the changes that are observed during the heat death of the whole animal, where exposure to 35°C produces a dramatic change in Na + permeability within five minutes. Arrhenius μ for heat death is also > 100 Kcals and operates over the identical critical temperature range. It is suggested that the Mg ++ ‐dependent ATPase controls passive permeability in these excitable cells and the results also confirm the view that Mg ++ and Na + ‐K + ‐Mg ++ ATPases are separate enzymes.