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Do organophosphorus compounds induce non-cholinergic cardiac dysfunction?
J Mol Cell Cardiol20
(Supplement
IV) (1988)
P-40DO
ORGANOPHOSPHORUS COMPOUNDS INDUCE NON-CHOLINERGIC CARDIAC DYSFUNCTION? P. Robin+, A. Corbier. Laboratoire de Pharmacodynamie, Centre d'Etudes du Bouchet, BP n'3, F91710 Vert le Petit, France. Organophosphorus compounds are powerful. inhibitors of cholinesterase. We recently have shown that, unexpectedly, these compounds could cause ventricular arrhythmias (Ventricular Premature Complexes, Torsades de pointe) in uiuo in rats and dogs. In the present work, we studied the effects of VX on isolated working rat hearts. The perfusion fluid was Krebs-Henseleit solution (pH 7.4) at 37°C. Left atria1 pressure and afterload were respectively 8 and 75 mm Hg. Either VX (34 ug.min-') or vehicle was delivered for 30 min using an infusion pump. The organophosphorus compound rapidly induced a decrease in heart rate (252 + 18 ud 346 + 8 beats.min-', after 5 min of VX infusion). The occurrence of arrhythmias was higher in the VX-treated hearts than in the control group (63.9% un 6.7%, for the whole infusion period). We compared these effects with those of carbachol. Carbachol (2.5 ug.min-' ) decreased heart rate (255 + 18 un 350 f. 12 beats.min-', after 5 min of carbachol infusion) similarly to VX, but caused a significantly lower occurrence of arrhythmias (20.0%). We suggest that, besides the expected. effects resulting from muscarinic stimulation, VX can directly affect cardiac muscle through a non-cholinergic mechanism. This could be an inhibition of the Nat- K+ ATPase of the cardiac cells, since this biochemical injury has already been reported in organophosphorus compound poisoning.
P-41
CHARACTERISTICS ATRIAL NODE.
Physiology,
OF CELLS ISOLATED H.F. Brown and
Parks Road, Gxford,
FTiOM DI-
AREAZ OF THE RABBIT
J.C. Denyer, OX1 3PT.
University
SINO-
Laboratory
of
Cells can be isolated from small pre-marked areas of the rabbit sino-atrial node by small modifications of the enzymic incubation method we have previously described. (Denyer &Brown, 1$%7, Jap. J. Physiol. 37, 963-965) Cells from different areas show morphological differences: those from most areas of the node are characteristically spindle-shaped with cell length increasing towards the periphery of the node while cells from a restricted central
region
of
the
node
show
different
shaped cells visible. Micrographs of both fresh and fixed with examples of electrical activity.
morphology
isolated
cells
with
will
few
be shown,
spindle-
together
P-@STUDIES ON THE REGULATORY PROPERTIES OF Ca2+-SENSITIVE DEHYDROGENASES WITHIN TOLUENEPERMEABILIZED RAT-HEART MITOCHONDRIA AND WITH PURIFIED ENZYMES. G.A. Rut&r and R.M. Denton, Department of Biochemistry, University of Bristol, BS8 1TD. Three exclusively mitochondrial enzymes, NAD+-isocitrate dehydrogenase (NAD-ICDH), Z-oxoglutarate dehydrogenase (OGDH), and the pyruvate dehydrogenase (PDH) cbmplex are Increases in cellular Ca '+-levels activated by pmolar concentrations of Ca'+-ions. may thus stimulate mitochondrial oxidative metabolism and ATP-synthesis at the same time as activating ATP-requiring processes, such as contraction. Investigations of the properties of the enzymes in situ are, however, hampered by the difficulty of assaying activity with precisi= within intact mitochondria. In order to circumvent these problems we have used toluene-permeabilized rat-heart mitochondria to compare in detail the kinetic properties of the enzymes in situ. -__ These studies have shown that: (1) the sensitivity to Ca*+ of NAD-ICDH may be considerably lower than that of OGDH or PDH assayed under identical conditions; (2) the Ca*+-sensitivity of NAD-ICDH and OGDH, but not PDH is increased with increases in the ADP/ATP ratio; (3) OGDH displays lower sensitivity to inhibition by NADH when assayed in permeabilized mitochondria than in extracts. Studies of purified NAD-ICDH and OGDH indicate that these enzymes differ markedly These differences in Cazf-sensitivity may be a device to in Ca*+-binding properties. allow flux through the citrate cycle to be controlled by a wide range of intramitochondrial Caz+ concentrations. s.50
(Supplement
IV) (1988)
P-40DO
ORGANOPHOSPHORUS COMPOUNDS INDUCE NON-CHOLINERGIC CARDIAC DYSFUNCTION? P. Robin+, A. Corbier. Laboratoire de Pharmacodynamie, Centre d'Etudes du Bouchet, BP n'3, F91710 Vert le Petit, France. Organophosphorus compounds are powerful. inhibitors of cholinesterase. We recently have shown that, unexpectedly, these compounds could cause ventricular arrhythmias (Ventricular Premature Complexes, Torsades de pointe) in uiuo in rats and dogs. In the present work, we studied the effects of VX on isolated working rat hearts. The perfusion fluid was Krebs-Henseleit solution (pH 7.4) at 37°C. Left atria1 pressure and afterload were respectively 8 and 75 mm Hg. Either VX (34 ug.min-') or vehicle was delivered for 30 min using an infusion pump. The organophosphorus compound rapidly induced a decrease in heart rate (252 + 18 ud 346 + 8 beats.min-', after 5 min of VX infusion). The occurrence of arrhythmias was higher in the VX-treated hearts than in the control group (63.9% un 6.7%, for the whole infusion period). We compared these effects with those of carbachol. Carbachol (2.5 ug.min-' ) decreased heart rate (255 + 18 un 350 f. 12 beats.min-', after 5 min of carbachol infusion) similarly to VX, but caused a significantly lower occurrence of arrhythmias (20.0%). We suggest that, besides the expected. effects resulting from muscarinic stimulation, VX can directly affect cardiac muscle through a non-cholinergic mechanism. This could be an inhibition of the Nat- K+ ATPase of the cardiac cells, since this biochemical injury has already been reported in organophosphorus compound poisoning.
P-41
CHARACTERISTICS ATRIAL NODE.
Physiology,
OF CELLS ISOLATED H.F. Brown and
Parks Road, Gxford,
FTiOM DI-
AREAZ OF THE RABBIT
J.C. Denyer, OX1 3PT.
University
SINO-
Laboratory
of
Cells can be isolated from small pre-marked areas of the rabbit sino-atrial node by small modifications of the enzymic incubation method we have previously described. (Denyer &Brown, 1$%7, Jap. J. Physiol. 37, 963-965) Cells from different areas show morphological differences: those from most areas of the node are characteristically spindle-shaped with cell length increasing towards the periphery of the node while cells from a restricted central
region
of
the
node
show
different
shaped cells visible. Micrographs of both fresh and fixed with examples of electrical activity.
morphology
isolated
cells
with
will
few
be shown,
spindle-
together
P-@STUDIES ON THE REGULATORY PROPERTIES OF Ca2+-SENSITIVE DEHYDROGENASES WITHIN TOLUENEPERMEABILIZED RAT-HEART MITOCHONDRIA AND WITH PURIFIED ENZYMES. G.A. Rut&r and R.M. Denton, Department of Biochemistry, University of Bristol, BS8 1TD. Three exclusively mitochondrial enzymes, NAD+-isocitrate dehydrogenase (NAD-ICDH), Z-oxoglutarate dehydrogenase (OGDH), and the pyruvate dehydrogenase (PDH) cbmplex are Increases in cellular Ca '+-levels activated by pmolar concentrations of Ca'+-ions. may thus stimulate mitochondrial oxidative metabolism and ATP-synthesis at the same time as activating ATP-requiring processes, such as contraction. Investigations of the properties of the enzymes in situ are, however, hampered by the difficulty of assaying activity with precisi= within intact mitochondria. In order to circumvent these problems we have used toluene-permeabilized rat-heart mitochondria to compare in detail the kinetic properties of the enzymes in situ. -__ These studies have shown that: (1) the sensitivity to Ca*+ of NAD-ICDH may be considerably lower than that of OGDH or PDH assayed under identical conditions; (2) the Ca*+-sensitivity of NAD-ICDH and OGDH, but not PDH is increased with increases in the ADP/ATP ratio; (3) OGDH displays lower sensitivity to inhibition by NADH when assayed in permeabilized mitochondria than in extracts. Studies of purified NAD-ICDH and OGDH indicate that these enzymes differ markedly These differences in Cazf-sensitivity may be a device to in Ca*+-binding properties. allow flux through the citrate cycle to be controlled by a wide range of intramitochondrial Caz+ concentrations. s.50