BIOCHEMICAL MEDICINE AND METABOLIC BIOLOGY 38, 366-377 (1987) Temperature-Dependent Abnormalities of the Erythrocyte Membrane in Porcine Malignant Hyperthermia HEMANT S. THATTE,’ PAUL B. ADDIS,’ DAVID D. THOMAS,~ DIANA J. BIGELOW,~ JAMES R. MICKELSON,~ AND CHARLES F. LOUISE Department of Veterinary Biology, University of Minnesota, 295 Animal Science/Veterinary Medicine Building, 1988 Fitch Avenue, St. Paul, Minnesota 55108 Received April 13, 1987 Arrhenius plots of membrane-bound enzyme activities have proven valuable in correlating changes in enzyme activity with the altered physical state of the cell membrane (1) as detected by a variety of biophysical techniques (2-5). A change in the apparent activation energy, as detected by a break in the Arrhenius plot, has been attributed to structural changes in the membrane (at the levels of proteins, lipids, or both), a conformational change in the enzyme, or a change in the nature of the rate-limiting step of the overall catalyzed reaction (6,7). After a number of differences of the erythrocyte ghost Ca-ATPase in malignant hyperthermia (MH) (8) were identified, it was appropriate to examine whether Arrhenius plots of erythrocyte membrane enzyme activities were also altered in this syndrome. In the present report we demonstrate that the Arrhenius plots of Ca-ATPase and calmodulin-stimulable Ca-ATPase acitvities are identical in MH and normal erythrocyte ghosts. In contrast, the temperature sensitivity of erythrocyte ghost Mg-ATPase activity differs in the two breeds of pig. Arrhenius plots of the motion of a spin-labeled stearic acid derivative (which probes the center of the membrane bilayer) were measured by electron paramagnetic resonance (EPR) in both erythrocytes and erythrocyte ghosts. Not only was the rate of motion of this derivative reduced in MH, but the apparent activation energy for probe motion was greater in normal than in MH-susceptible (MHS) erythrocyte ghosts. This contrasts with studies in intact erythrocytes where normal erythrocytes exhibited no breaks in Arrhenius plots of probe motion, while MHS erythrocytes exhibited breaks at 24 and 33°C. This demonstration of temperature-dependent ’ Present address: Division of Hematology, Department of Medicine, Stanford University School of Medicine, Stanford, CA 94305. ’ Present address: Department of Food Science and Nutrition, University of Minnesota, St. Paul, MN 55108. 3 Present address: Department of Biochemistry, University of Minnesota, St. Paul, MN 55108. 4 Present address: Department of Veterinary Biology. University of Minnesota, St. Paul, MN 55108. 366 0085-4505187 $3.00 Copyright 0 1987 by Academic Press, Inc. AI1 rights of reproduction in any form reserved.