The Temperature Characteristics of Brain Microsomal ATPases of the Hedgehog: Changes Associated with Hibernation

Abstract

studied in detail (Deul and McIlwain, 1961; Schwartz, Bachelard, and McI1wain, 1962; Skou, 1962; Aldridge, 1962; Jirnefelt, 1962, 1964; Whittam and Blond, 1964; Tanaka and Strickland, 1965; Albers, Arnaiz, and De Robertis, 1965; Davrainville and Gayet, 1966; Fujita et al., 1966; Palmer, Lasseter, and Melvin, 1966; Rendina, 1966; Robinson, 1967; Nakamaru, Kosakai, and Konishi, 1967). The two enzyme fractions may be differentially extracted (Nakao et al., 1963; Nakao et al., 1965) and so may represent separate enzyme systems (Bowler and Duncan, 1967). We have recently presented a detailed study of the effect of temperature on these two ATPase components from a rat brain microsomal preparation (Bowler and Duncan, 1968b). Arrhenius i plots showed that the two components had markedly differing temperature sensitivities and, further, that the enzyme activity of the Na+K+-Mg2+ ATPase was completely suppressed at temperatures below 5 C. However, in the poikilothermic frog, which will live and function normally at such temperatures, the Arrhenius t plot of the Na+-K+-Mg2+ ATPase of a brain microsomal preparation shows that enzyme activity continues at 1 C (Bowler and Duncan, 1968a). These results raise the question of the temperature sensitivity of the Na+K+-Mg2+ ATPase of the plasma membranes of hibernating mammals whose body temperature falls below 5 C (Kayser, 1961). If active cation transport is to continue during hibernation, enzyme activity of the Na+-K+-Mg2+ ATPase must not be supressed at these low temperatures. There appear to be two possible alternatives. Either hibernating mammals have a Na+-K+-Mg2+ ATPase whose temperature sensitivity resembles that of the poikilothermic frog, or, during preparation for hibernation, this enzyme is converted from the typical mammalian pattern into one in which enzyme activity continues below 5 C. In the present experiments the temperature sensitivity of the ATPases of a microsomal preparation from the brains of hedgehogs, using