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A mechanism for the early loss of potassium from the hypoxic or ischaemic myocardium
J Mol Cell Cardiol 18 (Supplement 1) (1986) I08GLUCOSE AND FFA AS MYOCARDIAL SUBSTRATE DURING ISCMAEMIA: EFFECTS ON GLUTATHIONE STATUS. R. Ferrari, S. Curello, C. Ceconi. Universita' degli Studi di Brescia, Cattedra di Cardiologia, Brescia, Italy. It is known that substrate availability during ischaemia plays a role in the evolution of heart damage, FFA inducing a severe impairment of metabolic and mechanical function. We have investigated the effects of palmitate or glucose availability during ischaemia on reduced and oxidized glutathione (GSH and GSSG) status. Isolated and perfused rabbits hearts were made ischaemic (30 min) reducing coronary flow from 25 to 3 ml/min followed by 30 min of reperfusion (R). Palmitate (1.2 mM) or glucose (ii mM) were used as ischaemie substrates. With glucose on R there was a complete recovery of developed pressure, small CPK release, no changes in mitochondrial function or in tissue levels of GSH and GSSG. When palmitate was used, the recovery of pressure was less than 20% with massive contracture and CPK release. Mitochondrial function was impaired and there was a release of GSSG concomitant with an increase of its tissue contents. Tissue levels of GSH were severely reduced, leading to a reduction of GSH/GSSG below i0. These data suggest that when palmitate was used as ischaemic substrate there was a shift of the redox state of glutathione suggesting that an oxidative stress has occurred.
I O g s A R C O L E M M A L PERMEABILITY IN THE ISCHAEMIC RAT HEART: QUANTIFICATION USING A LANTHANUM PROBE. A. Lochner , I.S. Harper , M. de Villiers . ~s Insitute for Electron Microscopy, Tygerberg and MRC Unit for Molecular and Cellular Cardiology, University of Stellenbosch Medical School, Tygerberg, South Africa. Changes in the permeability of the sarcolemma during early ischaemia have been examined in the isolated rat heart using a lanthanum probe method. Hearts perfused retrogradely are made globally ischaemic for various periods (I0 - 40 min) and then perfused with 5 m M LaCI in a non-nutritive saline solution for 10 minutes, This solu3 tion does not allow reperfuslon recovery or further damage jeopardized tissue. Hearts were perfusion-fixed and processed as for routine transmission electron microscopy. Lanthanum is not entirely excluded from control (non-ischaemic) tissue: some myocytes contain sparsely scattered lanthanum particles over myofibrils, particularly over the I and Z bands, while other cell~ are devoid of intracellular lanthanum. Only after 15 minutes of total ischaemia regions of the subendocardium have distinct intracellular deposits of lanthanum located within mitochondria, over the myofibrils and in the cytosol. As ischaemia continues the altered cell membrane permeability, as reflected by this infldm of lanthanum into myocytes, gradually becomes apparent in the subepicardium as well. These observations are supported by quantified data and illustrate that changes in sarcolemmal permeability are an early event in myocardial ischaemia, occurring prior to the onset of irreversible damage and spreading from subendocardium to subepicardium.
~ I O A MECHANISM FOR THE EARLY LOSS OF POTASSIUM FROM THE HYPOXIC OR ISCHAEMIC MYOCARDIUM. A. G a s p a r d o n e , S.R. Seabrooke, P.A. P o o l e - W i l s o n . C a r d i o t h o r a c i c I n s t i t u t e and National Heart Hospital, 2 Beaumont Street, London WIN 2DX, UK. A net loss of potassium from the myoeardium occurs almost immediately after the onset of ischaemia or hypoxia. We h a v e tested w h e t h e r this loss is r e l a t e d to changes in intracellular osmolality or to the outward movement of negatively charged molecules generated by anaerobic metabolism. The experimental preparation was the i n t e r v e n t r i c u l a r s e p t u m of the rabbit s t i m u l a t e d at 85-95 b e a t s / m i n at 30~ and perfused with a physiological solution containin~ 5 m M K +. Hypoxic substrate free p e r f u s i o n for 15 m i n u t e s caused a net loss of K (7 Z 1 m m o l / k g wet tissue, n=6) w h i c h was due to an increased e f f l u x of K +. I n f l u x of K + was u n a l t e r e d o v e r this period. Perfusion with hyperosmolar solutions (addition of 60 m M sucrose or 30 m M NaCI) caused a reversible net gain of K + attributable to an increase of influx with no change of efflux. P e r f u s i o n w i t h s o l u t i o n c o n t a i n i n g 114 m M i s e t h i o n a t e (in e x c h a n g e for CI-) or 30 m M i s e t h i o n a t e after e q u i l i b r a t i o n w i t h the inert but p e r m e a n t a n i o n D M O - (30 mM) caused an increased e f f l u x of K + (net loss after 15 m i n u t e s 5.4 ~0.3 (n=6) and 4,0 ~0.2 (n=3) m m o l / k g wet tissue r e s p e c t i v e l y ) w i t h o u t any effect on influx (n=5). The early loss of K § can largely be accounted for by an efflux of K + linked to the outward movement of negatively charged molecules in the absence of damage to the cell membrane. Supported by the CNR Italy and the BHF UK.
I O g s A R C O L E M M A L PERMEABILITY IN THE ISCHAEMIC RAT HEART: QUANTIFICATION USING A LANTHANUM PROBE. A. Lochner , I.S. Harper , M. de Villiers . ~s Insitute for Electron Microscopy, Tygerberg and MRC Unit for Molecular and Cellular Cardiology, University of Stellenbosch Medical School, Tygerberg, South Africa. Changes in the permeability of the sarcolemma during early ischaemia have been examined in the isolated rat heart using a lanthanum probe method. Hearts perfused retrogradely are made globally ischaemic for various periods (I0 - 40 min) and then perfused with 5 m M LaCI in a non-nutritive saline solution for 10 minutes, This solu3 tion does not allow reperfuslon recovery or further damage jeopardized tissue. Hearts were perfusion-fixed and processed as for routine transmission electron microscopy. Lanthanum is not entirely excluded from control (non-ischaemic) tissue: some myocytes contain sparsely scattered lanthanum particles over myofibrils, particularly over the I and Z bands, while other cell~ are devoid of intracellular lanthanum. Only after 15 minutes of total ischaemia regions of the subendocardium have distinct intracellular deposits of lanthanum located within mitochondria, over the myofibrils and in the cytosol. As ischaemia continues the altered cell membrane permeability, as reflected by this infldm of lanthanum into myocytes, gradually becomes apparent in the subepicardium as well. These observations are supported by quantified data and illustrate that changes in sarcolemmal permeability are an early event in myocardial ischaemia, occurring prior to the onset of irreversible damage and spreading from subendocardium to subepicardium.
~ I O A MECHANISM FOR THE EARLY LOSS OF POTASSIUM FROM THE HYPOXIC OR ISCHAEMIC MYOCARDIUM. A. G a s p a r d o n e , S.R. Seabrooke, P.A. P o o l e - W i l s o n . C a r d i o t h o r a c i c I n s t i t u t e and National Heart Hospital, 2 Beaumont Street, London WIN 2DX, UK. A net loss of potassium from the myoeardium occurs almost immediately after the onset of ischaemia or hypoxia. We h a v e tested w h e t h e r this loss is r e l a t e d to changes in intracellular osmolality or to the outward movement of negatively charged molecules generated by anaerobic metabolism. The experimental preparation was the i n t e r v e n t r i c u l a r s e p t u m of the rabbit s t i m u l a t e d at 85-95 b e a t s / m i n at 30~ and perfused with a physiological solution containin~ 5 m M K +. Hypoxic substrate free p e r f u s i o n for 15 m i n u t e s caused a net loss of K (7 Z 1 m m o l / k g wet tissue, n=6) w h i c h was due to an increased e f f l u x of K +. I n f l u x of K + was u n a l t e r e d o v e r this period. Perfusion with hyperosmolar solutions (addition of 60 m M sucrose or 30 m M NaCI) caused a reversible net gain of K + attributable to an increase of influx with no change of efflux. P e r f u s i o n w i t h s o l u t i o n c o n t a i n i n g 114 m M i s e t h i o n a t e (in e x c h a n g e for CI-) or 30 m M i s e t h i o n a t e after e q u i l i b r a t i o n w i t h the inert but p e r m e a n t a n i o n D M O - (30 mM) caused an increased e f f l u x of K + (net loss after 15 m i n u t e s 5.4 ~0.3 (n=6) and 4,0 ~0.2 (n=3) m m o l / k g wet tissue r e s p e c t i v e l y ) w i t h o u t any effect on influx (n=5). The early loss of K § can largely be accounted for by an efflux of K + linked to the outward movement of negatively charged molecules in the absence of damage to the cell membrane. Supported by the CNR Italy and the BHF UK.