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A monovalent cation-selective channel of sheep cardiac muscle sarcoplasmic reticulum (SR)
j Mol Cell Cardiol 18 ( S u p p l e m e n t 1) (1986) 99A
MONOVAL]~{TCATION-SELECTIVE Clq_ANNELOF S ~ CARDIAC MUSCLE SARC0PLASMIC RETICULUM A.J. Williams, M.A. Gray, RAP Montgomery. D e p a r t e m e n t o f C a r d i a e M e d i c i n e , The C a r d i o t h o r a c i e I n s t i t u t e , 2 Beaumont S t r e e t , London W1N 2DX.
(SR).
0xalate loaded SR vesicles were p r e p a r e d from sheep heart using the m e t h o d of Jones and Cala (J. Biol. C h e m 256;809-818, 1981). Vesicles were induced to fuse w i t h p r e f o r m e d planar p h o s p h o l i p i d bilayers and single channel fluctuations m o n i t o r e d under voltage clamp conditions as previously described (Tomlins et al J. Hemb. Biol. 80;191-199, 1984). Sheep SR vesicles contain a monovalent cation-selective channel. In the presence of symmetrieal 7 5 m M K ~ S 0 a the channel behaves ohmically w i t h a single channel conductance of the fully 6pen state of 17~ ~ 19 pS. In addition, the channel displays a sub-conductance state, the conductance of which is 60-70% of that of the fully open state. K§ conductance through the channel is blocked from one side of the membrane by gallamine. The zero voltage dissociation constant (kbo) for block is in the range 291-515 ~M at gallamine concentrations ranging~from 50-200 ~M. The basic conductance properties of this channel closely resemble those of the rabbit SR channel (Tomlins et al 1984). However the kbo for gallamine block is approximately 6 fold greater than that observed w i t h the rabbit channel. Supported by the British H e a r t Foundation.
IOOABILITY Ce 6 " A m X ~ RADICAL" I ~ ( ] N S TO REIN~ R E P E ~ I C N - I ~ ARR}~ ADDITION CF A FREE RADICAL GEREPATLNS SYS~I~. M.Bersier, D.J. Hearse, A.S. Mar~irO. The Heart Research Unit. The Rayne Institute. St Tnog~s' Hospital. ~ SEI 7EH. U.K.
CAUSED
BY
We have shown previously that the incidence of reperfusicn-indueed a r r h ~ a s can be increased dravatically by the addition of a free radical generating system (0.1 ~M FeCI5. 1 pM ADP) to the perfusion fluid. Associated with this increase in rhythm disturbances is a significant reduction in the mean duration of normal sinus rhythm during the reperfusion period. In this study, we have assessed whether 6 agents that either inhibit free radical formation or scavenge free radicals once they are produced, can reduce t ~ incidence of reperfusion-induced arrhythmias caused by the addition of the free radical generating system FeCI~.ADP to the perfusion fluid. Using the isolated, perfused rat heart (n=15 in each grot~p), inclusion of s/peroxide dismutase (O.iUnit/litre), catalase (i Unit/litre), glutathiose (10 ~M), ~ennitol (50 /aM), methionine (I0 raM) or desferrioxamise (150 IIM) all reduced significantly the incidence of reperfusicn-induced ventricular fibrillation (from 80% to between 0 and 20%) and ventricular tachycardia (from 80% to between 13 and 40%). The mean time that each of the above grot~ps re~ained in normal sinus rhythm during the reperfusion period was also significantly increased, and the ntm~er of PVC's was significantly reduced by all the "anti-free radical" ieterventions used. These results are further evidence in support of the hypothesis that free radicals play an important role in the genesis of reperfusion-indnced arrhythmias.
1 0 1 FACTORS INFLUENCING INFARCT SIZE: IS CORONARY COLLATERAL FLOW THE KEY DETERMINANT? D M Yellon*, T Miura, D J Hearse*, and J M DoWney. University of South Alabama, Mobile, Alabama. U.S.A. and *The Rayne Institute, St Thomas' Hospital, London, UK. We conducted 85 experiments in which a coronary branch was embolized in closed chest dogs for either 24 or 48h. The size of the resulting infarct was measured by tetrazolium staining of sequential 3-5 mm sections. The zone at risk was defined as the field of the occluded branch and was measured by microsphere autoradiography. The data was examined to determine factors which correlated with infarct size. When infarct size was expressed as a percentage of the risk zone (I/R), it was found to be independent of the sex of the animal, the time of year, the branch embolized (LAD or circumflex), and the duration of elapsed ischemia (24 or 48h). Risk zone size ragged from 1.5 to 42.0 percent of the ventricular muscle volume. Infarct size (in cm ~) was found to = [0.76 x risk zone size - 0.41l, the correlation coefficient was 0.92. Since the axis intercept was not significantly different from zero, I/R should be independent of the risk zone size. This was found to be the case, and I/R averaged 72.8 + 18.8 percent (SD) for the entire group, including 74 hearts having risk zones i~volving less than 20 percent of the ventricle. Infarct size correlated closely with the amount of collateral flow in the risk zone immediately following occluslon. The best fit (I/R = [90.0 - 0.9 x %CF], r = 0.93) occurred when collateral flow to the subepicardial third of the wall was expressed as a percentage of flow in the nonischemic tissue (%CF). In the absence of any intervention, the ultimate size of an infarct can be accurately predicted simply on the basis of collateral flow at the onset of ischemia and this can be done without any regard to risk zone size.
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MONOVAL]~{TCATION-SELECTIVE Clq_ANNELOF S ~ CARDIAC MUSCLE SARC0PLASMIC RETICULUM A.J. Williams, M.A. Gray, RAP Montgomery. D e p a r t e m e n t o f C a r d i a e M e d i c i n e , The C a r d i o t h o r a c i e I n s t i t u t e , 2 Beaumont S t r e e t , London W1N 2DX.
(SR).
0xalate loaded SR vesicles were p r e p a r e d from sheep heart using the m e t h o d of Jones and Cala (J. Biol. C h e m 256;809-818, 1981). Vesicles were induced to fuse w i t h p r e f o r m e d planar p h o s p h o l i p i d bilayers and single channel fluctuations m o n i t o r e d under voltage clamp conditions as previously described (Tomlins et al J. Hemb. Biol. 80;191-199, 1984). Sheep SR vesicles contain a monovalent cation-selective channel. In the presence of symmetrieal 7 5 m M K ~ S 0 a the channel behaves ohmically w i t h a single channel conductance of the fully 6pen state of 17~ ~ 19 pS. In addition, the channel displays a sub-conductance state, the conductance of which is 60-70% of that of the fully open state. K§ conductance through the channel is blocked from one side of the membrane by gallamine. The zero voltage dissociation constant (kbo) for block is in the range 291-515 ~M at gallamine concentrations ranging~from 50-200 ~M. The basic conductance properties of this channel closely resemble those of the rabbit SR channel (Tomlins et al 1984). However the kbo for gallamine block is approximately 6 fold greater than that observed w i t h the rabbit channel. Supported by the British H e a r t Foundation.
IOOABILITY Ce 6 " A m X ~ RADICAL" I ~ ( ] N S TO REIN~ R E P E ~ I C N - I ~ ARR}~ ADDITION CF A FREE RADICAL GEREPATLNS SYS~I~. M.Bersier, D.J. Hearse, A.S. Mar~irO. The Heart Research Unit. The Rayne Institute. St Tnog~s' Hospital. ~ SEI 7EH. U.K.
CAUSED
BY
We have shown previously that the incidence of reperfusicn-indueed a r r h ~ a s can be increased dravatically by the addition of a free radical generating system (0.1 ~M FeCI5. 1 pM ADP) to the perfusion fluid. Associated with this increase in rhythm disturbances is a significant reduction in the mean duration of normal sinus rhythm during the reperfusion period. In this study, we have assessed whether 6 agents that either inhibit free radical formation or scavenge free radicals once they are produced, can reduce t ~ incidence of reperfusion-induced arrhythmias caused by the addition of the free radical generating system FeCI~.ADP to the perfusion fluid. Using the isolated, perfused rat heart (n=15 in each grot~p), inclusion of s/peroxide dismutase (O.iUnit/litre), catalase (i Unit/litre), glutathiose (10 ~M), ~ennitol (50 /aM), methionine (I0 raM) or desferrioxamise (150 IIM) all reduced significantly the incidence of reperfusicn-induced ventricular fibrillation (from 80% to between 0 and 20%) and ventricular tachycardia (from 80% to between 13 and 40%). The mean time that each of the above grot~ps re~ained in normal sinus rhythm during the reperfusion period was also significantly increased, and the ntm~er of PVC's was significantly reduced by all the "anti-free radical" ieterventions used. These results are further evidence in support of the hypothesis that free radicals play an important role in the genesis of reperfusion-indnced arrhythmias.
1 0 1 FACTORS INFLUENCING INFARCT SIZE: IS CORONARY COLLATERAL FLOW THE KEY DETERMINANT? D M Yellon*, T Miura, D J Hearse*, and J M DoWney. University of South Alabama, Mobile, Alabama. U.S.A. and *The Rayne Institute, St Thomas' Hospital, London, UK. We conducted 85 experiments in which a coronary branch was embolized in closed chest dogs for either 24 or 48h. The size of the resulting infarct was measured by tetrazolium staining of sequential 3-5 mm sections. The zone at risk was defined as the field of the occluded branch and was measured by microsphere autoradiography. The data was examined to determine factors which correlated with infarct size. When infarct size was expressed as a percentage of the risk zone (I/R), it was found to be independent of the sex of the animal, the time of year, the branch embolized (LAD or circumflex), and the duration of elapsed ischemia (24 or 48h). Risk zone size ragged from 1.5 to 42.0 percent of the ventricular muscle volume. Infarct size (in cm ~) was found to = [0.76 x risk zone size - 0.41l, the correlation coefficient was 0.92. Since the axis intercept was not significantly different from zero, I/R should be independent of the risk zone size. This was found to be the case, and I/R averaged 72.8 + 18.8 percent (SD) for the entire group, including 74 hearts having risk zones i~volving less than 20 percent of the ventricle. Infarct size correlated closely with the amount of collateral flow in the risk zone immediately following occluslon. The best fit (I/R = [90.0 - 0.9 x %CF], r = 0.93) occurred when collateral flow to the subepicardial third of the wall was expressed as a percentage of flow in the nonischemic tissue (%CF). In the absence of any intervention, the ultimate size of an infarct can be accurately predicted simply on the basis of collateral flow at the onset of ischemia and this can be done without any regard to risk zone size.
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