1020 ity of the skeletal muscle. Matkovics and Nowak 14 also found that the activity of the peroxidase assayed (EC 1.11.1.7) was higher in the H202-supplied group in kidney and skeletal muscle whereas our results from the assay for Se-dependent GSHPx (EC 1.11.1.9)showed a decrease in the enzyme activity of kid- ney, liver and skeletal muscle. The experimental design of Mat- kovics and Novfik 14 was similar to ours but they used the CFY- strain of rats and they had no water-deprived group similar to ours. The GSHPx inhibits lipid peroxidation in vitro 15. Selenium is necessary for the H202 decomposing activity of Se-dependent GSHPx and various organs contain different amounts of Se and Se-dependent GSHPx activities. For example, rat kidney con- tains Se 1.45 mg-kg -1, liver 1.29 mg.kg -1, heart 0.37 mg-kg -1 and muscle 0.16 mg.kg -1 16. The activity of Se-dependent GSHPx changes logarithmically in several tissues of rat with respect to the Se concentration in the diet 17. The liver and kid- neys are the organs most susceptible to degeneration induced by Se deficiency, whilst abnormalities in heart are rare is. H202 as an oxidizing agent could have an effect on the oxidization of the biologically effective organic selenium compounds of the food to inorganic derivatives which are not so bio-available Is. This re- duces the Se intake and causes a decrease in the activity of Se-dependent GSHPx. Smith et al. ~9 found a reduced activity of GSHPx (cumene hydroperoxide as substrate) in kidney, red cells and liver in Se deficiency. The effects of Se deficiency, as well as those of oral HzO2-supply , are highly selective in various tissues, which suggests tissue differences in antioxidant regulation. Experientia 42 (1986), Birkhfiuser Verlag, CH-4010 Basel/Switzerland 1 Matkovics, B., Novfik, R., Szab6, L., Marik, M., and Zsoldos, T., Gen. Pharmac. 9 (1978) 329. 2 Valenzuela, A., Fernandez, N., Fernandez, V., Ugarte, G., and Vi- dela, L.A., FEBS Lett. Ill (1980) 11. 3 Hahn, H.K.J., Barak, A.J., Tuma, D.J., and Sorrell, M.F., Bio- chem. Pharmac. 26 (1977) 164. 4 Ursini, F., Maiorino, M., Ferri, L., Valente, M., and Gregolin, C., J. inorg. Biochem. 15 (1981) 163. 5 Kutkarni, A. P., and Hodgson, E., Int. J. Biochem. 13 (198i) 811. 6 Lawrence, R. A, and Burk, R. F., J. Nutr. 108 (1978) 211. 7 Jakoby, W.B., in: Advances in Enzymology, Vol. 46, p. 383. Ed. A. Meister. John Wiley & Sons, New York 1978. 8 Hoekstra, W. G., Fedn. Proc. 34 (1975) 2083. 9 Lee, Y.H., Layman, D.K., Bell, R. R., and Norton, H.W., J. Nutr. 111 (1981) 2195. 10 Leighton, F, Poole, B., Beaufay, H., Baudhuin, P., Coffey, J.W., Fowler, S., and DeDuve, C., J. Cell Biol. 37 (1968) 482. 11 Paglia, D. E., and Valentine, W. N., J. Lab. clin. Med. 70 (1976) 158. 12 Barrett, A.J., in: Lysosomes, A Laboratory Handbook, p.46. Ed. J.T. Dingle. Elsevier/North Holland, Amsterdam 1972. 13 Lowry, O.H., Rosebrough, N.J., Farr, A.L., and Randall, R.J., J. biol. Chem. 193 (1951) 265. 14 Matkovics, B., and Nov~tk, R., Experientia 33 (1977) 1574. 15 Burk, R. F., Trumble, M.J., and Lawrence, R. A., Biochim. biophys. Acta 618 (1980) 35. 16 Behne, D., and Wolters, W., J. Nutr. 113 (1983) 456. 17 Chow, C.K., and Tappel, A.L., J. Nutr. 104 (1974) 444. 18 Schwarz, K., Fedn. Proc. 20 (1970) 666. 19 Smith, P.J., Tappel, A. C., and Chow, C. K., Nature 247 (1974) 392. 0014-4754/86/091018-0351.50 + 0.20/0 ?9 Birkh/iuser Verlag Basel, 1986 Altered K + movement in liver mitochondria from alloxan diabetic rats R.A. Garrick Fordham University, The College at Lincoln Center, Division of Science and Mathematics, 113 W. 60th Street, New York (New York 10023, USA), 28 October 1985 Summary. Potassium movements were monitored in liver mitochondria from control and alloxan diabetic rats with a cationic electrode. There was net accumulation of K + after Ca 2+ addition to the mitochondria with the diabetic but not with the control. Key words. Diabetes; K+; mitochondrial permeability; energy metabolism. Liver mitochondria from alloxan diabetic rats were used to assess cellular energy production in the diabetic state 1'2. Stimu- lation of respiration by addition of adenosine diphosphate (ADP) and Ca 2+ to the mitochondria and the production of ATP or accumulation and retention of Ca 2+ by mitochondria are standard methods for evaluating mitochondrial energy produc- tion 3. The diabetic mitochondria are less efficient in energy pro- duction than mitochondria from untreated rats I and the accu- mulation and retention of Ca 2+ in the diabetic mitochondria is lower than in normal mitochondria 2. Changes in the ionic com- position of the medium helped to elucidate these differences and indicated that a description of the interaction of K + with the mitochondria could help explain the altered pattern in the dia- betic mitochondria 2. In an earlier study the ionic content of the mitochondria was measured after a set incubation time using a flame photometer 2. In that study changes in respiration were followed continuously and indicated that a continuous monitoring of changes in mito- chondrial K + would be informative. Consequently the studies reported here were performed with continuous monitoring of net K + flux in mitochondria with a K + electrode. The patterns of K + flux in normal and diabetic mitochondria before and after Ca 2+ stimulation are reported here. The purpose of these studies was to determine the pattern of K + movement in the diabetic state compared to control animals and to correlate these, if different from normal, to changes reported in the diabetic animal. Methods. Care and preparation of the rats and preparation of the mitochondria (in 0.25 M sucrose) were described previously 1. Potassium movements were monitored continuously with a Beckman Cationic e!ectrode (No. 39137) and a n Orion 701 digital pH meter and recorded on a Strip Chart. The response of the electrode to various incubation medium components and to pH changes was evaluated to confirm that the changes monitored were those due to K + levels only. Mitochondria were incubated in 6 ml of medium containing: 100 mM choline chloride, 50 mM Tris HCI (tris(hydroxymethyl)aminomethane), 5 mM Tris suc- cinate, 4 mM KC1, and 6-7 mg of mitochondrial protein/ml with a total osmolarity of 300 mosmoles. After equilibration, 0.5 mM CaCI 2 (80 nmoles/mg protein) was added and continuous recordings made for at least 5 min to monitor the changes in medium K + after Ca 2+ addition. It should be noted that net K + movements are monitored in this system and increased influx and efflux of K + is measured only if there is a net change in medium content of K + due to these movements. Volume changes in mitochondria as reflected by changes in absorption 4, which have been described as phase 1 or low ampli- tude changes, were monitored with a Perkin-Elmer Spectropho- tometer at 520 nm and recorded on a strip chart. The incubation medium of 3 ml contained 225 mM sucrose, 20 mM Tris HC1, 5 mM succinate and 1 mg mitochondrial protein/ml. These vol- ume changes occur as a normal part of the cycle seen in stimu- lated and resting mitochondira and are reversible 3. After equili- bration calcium or phosphate was added and the changes moni-
