Red cell and plasma antioxidant components and atherosclerosis in Japanese quail: a time-course study.

Our study aims to examine changes in red cell and plasma antioxidant components in relation to age and aortic lesion development in SUS Japanese quail during a 12-week period of dietary cholesterol supplementation. One hundred adult SUS males were divided into 5 treatment groups and were fed either a control or a cholesterol-supplemented (0.5% w/w) diet. Birds were sacrificed after 0, 4, 8 and 12 weeks on the diets and examined for plaque development and antioxidant components status. "Aging" was associated with increases in the activity of red cell SOD and GPx. Significant correlations among red cell GRd, GPx and SOD activities were found in old but not in younger adult birds. Plasma triglyceride levels increased, while plasma tocopherol level decreased with aging. With birds on the cholesterol diet, plaque score increased with time and regressed significantly but negatively on plasma cholesterol level at the initial stage of atherogenesis. Aortic triglycerides showed a drastic increase in the early stage of atherogenesis but returned to the pretreatment level during the late stage. Conversely, aortic cholesterol showed small increases at the early stages but large increases during the late stage. Red cell antioxidant components showed increases at the early and late stages with a leveling off at the mid stage. Plasma GRd activity decreased while plasma tocopherol level increased (after adjusting for the effect of effect of aging) with cholesterol feeding. We conclude that the increase in plasma triglyceride levels and associations among red blood cell GRd, GPx and SOD activities in "old" birds fed the control diet resembled the situation in the early stages of atherogenesis in the cholesterol-fed birds. This would be consistent with the known permissive effect of aging on the course of atherogenesis. Triglycerides may play a crucial role in atherogenesis during the early phase of lesion development. Early and late phases of lesion development are biochemically distinct, indicating that the process of atherogenesis is a highly dynamic one. The patterns of antioxidant alterations associated with lesion development showed a complex time-dependence.

High dose propofol enhances red cell antioxidant capacity during CPB in humans.

PURPOSE: To compare low vs. high dose propofol and isoflurane on red cell RBC antioxidant capacity in patients during aortocoronary bypass surgery (ACBP). METHODS: Twenty-one patients, for ACBP, were anesthetized with sufentanil 0.5-10 microg x kg(-1) and isoflurane 0-2%; ISO = control; n = 7), or sufentanil 0.3 microg x kg(-1), propofol 1-2.5 mg x kg(-1) bolus then 100 microg x kg(-1) min(-1) before, and 50 microg x kg(-1) x min(-1) during CPB (LO; n = 7), or sufentanil 0.3 microg x kg(-1), propofol 2-2.5 mg x kg(-1) bolus then 200 microg x kg(-1) x min(-1) (HI; n = 7). Venous blood was drawn pre- and post-induction, after 30 min CPB, 5, 10, and 30 min of reperfusion, and 120 min post-CPB to measure red cell antioxidant capacity (malondialdehyde (MDA) production in response to oxidative challenge with t-butyl hydrogen peroxide) and plasma propofol concentration. Pre- induction blood samples were analyzed for antioxidant effects of nitrates on red cells. The tBHP concentration response curves for RBC MDA in ISO, LO and HI were determined. RESULTS: Preoperative nitrate therapy did not effect RBC MDA production. Perioperative RBC MDA production was similar in ISO and LO groups. Sustained intraoperative decrease in RBC MDA was seen with propofol 8.0+/-2.4 - 11.8+/-4.5 microg x ml(-1) in HI (P<0.05-0.0001). MDA production vs. log plasma propofol concentration was linear in HI dose. CONCLUSIONS: During CPB, RBC antioxidant capacity is enhanced and maintained with HI dose propofol. Propofol, at this dose, may prove useful in protecting against cardiopulmonary ischemia-reperfusion injury associated with ACBP.

Dietary cholesterol-induced xanthomatosis in atherosclerosis-susceptible Japanese quail (Cotunix japonica).

Japanese quail of a strain (SUS) susceptible to dietary cholesterol-induced atherosclerosis were fed a diet supplemented with cholesterol (0.5% w/w) for 4, 8 or 12 weeks. Plasma cholesterol increased significantly from 240-1550 mg/dl at 4 weeks and remained at that concentration for 8 and 12 weeks on the same diet. Plasma triglycerides (TGs) increased from 112-384 mg/dl after 4 weeks but showed no significant increases thereafter. Striking eruptive xanthomatous lesions were noticed on the feet of 50% of these birds at 4 weeks, and the percentage of birds affected increased to 85 after 12 weeks on the cholesterol-supplemented diet. This is the first report of xanthomatosis in birds. These birds had also developed atherosclerotic plaques in the aorta and brachiocephalic arteries by 4 weeks. There was no significant correlation between xanthoma scores and plasma cholesterol and TG concentrations at any of the three sampling periods (4, 8 and 12 weeks of cholesterol feeding). There was, however, a significant negative correlation (r = -0.61) between xanthoma scores and atherosclerotic plaque scores at 4 weeks. The correlation became non-significant at later stages of cholesterol exposure. Similarities between mammalian and SUS Japanese quail xanthomatosis may make the SUS quail a useful model for the study of this disorder.

Propofol enhances red cell antioxidant capacity in swine and humans.

PURPOSE: To determine the effect of an anaesthetic with antioxidant potential, propofol, on red blood cell (RBC) antioxidant enzyme activities and RBC susceptibility to peroxidative challenge. METHODS: Propofol was administered by intravenous bolus (2.5 mg.kg-1) and continuous infusion (36 and 72 ml.hr-1 in nine swine; 216 ml.hr-1 in two swine), to achieve serum concentrations between 5 and 30 micrograms.ml-1 for two hours at each rate. Arterial blood sampling was at 0, 10, 30, 60, and 120 min for each rate of infusion, for measurement of plasma propofol concentration, activities of plasma and RBC superoxide dismutase, glutathione peroxidase, glutathione reductase, RBC catalase, and RBC malondialdehyde (MDA) formation in response to ex vivo oxidative challenge with t-butyl hydrogen peroxide (tBHP; 1.5 mM). Antioxidant mechanisms were determined by in vitro study of MDA formation, GSH depletion, and oxidation of haemoglobin to methaemoglobin in human erythrocytes exposed to propofol 0-75 microM. The antioxidant potential of propofol was compared with that of alpha-tocopherol utilising the reaction with 2,4,6-tripyridyl-s-triazine (TPTZ). RESULTS: Propofol had no effect on plasma or RBC antioxidant enzyme activities. It inhibited RBC MDA production over the range of 0-20 micrograms.ml-1 (y = -18.683x + 85.431; R2 = 0.8174). Effective propofol concentrations for 25% and 50% reductions in MDA levels were 7-12 and 12-20 micrograms.ml-1, respectively. Propofol has a similar effect on human erythrocytes in vitro (R2 = 0.98). CONCLUSION: Propofol antagonises the effects of forced peroxidation of red cells at anaesthetic and sub-anaesthetic concentrations in swine. Its actions include scavenging of oxygen derived free radicals in a tocopherol-like manner.

Antioxidant enzymes and atherosclerosis in Japanese quail: heritability and genetic correlation estimates.

OBJECTIVES: To estimate, in male quail susceptible to atherosclerotic plaque formation (SUS) fed a regular diet and an atherogenic diet, the genetic and phenotypic parameters associated with antioxidant enzymes and atherogenesis. DESIGN: Genetic parameters were estimated from variance components of the analysis of variance on 70 males from 13 full-sib families. MAIN RESULTS: Under the regular diet, seven of 35 males developed mild atherosclerosis. Heritability was zero for atherosclerotic plaque score and plasma cholesterol level. Plaque score was highly correlated to plasma triglyceride level (rp = 0.96) and liver fattiness (rp = 0.97), but only moderately to plasma cholesterol level (rp = 0.39). With the high cholesterol diet, plasma cholesterol level increased sixfold and became heritable (h2 = 0.4). Many males developed severe atherosclerosis. Plaque score became associated more with plasma and aortic cholesterol levels (rp = 0.56) and 0.76, respectively) than with plasma triglyceride level (rp = 0.54). Aortic glutathione reductase activity was negatively correlated with plaque score (rp = -0.42; rg = -0.51) and aortic cholesterol level (rp = -0.39; rg = -0.62). CONCLUSIONS: Plasma triglyceride level was an important factor affecting the development of fatty streaks and the early progression of atherosclerotic plaques. Without high levels of dietary cholesterol in the plasma and aorta, any early atherosclerotic plaques that developed did not progress further within the time-frame of the experiment. Aortic cholesterol concentration and glutathione reductase activity were important factors in the advancement of severe plaque formation. Heritability of plaque score was high in the SUS line, and further selective breeding should increase the susceptibility of these quail to cholesterol-induced atherosclerosis.

Sex-related alterations in antioxidant status and susceptibility to atherosclerosis in Japanese quail.

OBJECTIVE: To examine antioxidant enzyme activities in aorta and blood of male and female Japanese quail on control or cholesterol-supplemented diets, given the strong influence of sex and the postulated role of oxidative processes in the pathogenesis of atherosclerosis. ANIMALS AND METHODS: Atherosclerosis-prone Japanese quail (15 of each sex) were either maintained on a control diet or fed a cholesterol-supplemented (1% by weight) diet for nine weeks. RESULTS: Plasma cholesterol levels in controls were comparable in both sexes, although females showed higher triglyceride levels. Cholesterol supplementation increased plasma cholesterol in both males (8.1-fold) and females (2.5-fold) but triglycerides were significantly elevated (3.4-fold) by cholesterol feeding only in males. Cholesterol supplementation increased aortic cholesterol content to a greater extent in males (2.2-fold) than in females (1.4-fold) and plaque formation was apparent only in males. Cholesterol-fed birds showed small, but significant, sex-related differences in antioxidant enzyme profiles of aorta (glutathione peroxidase activity was higher in males and superoxide dismutase activity was lower in females) and red blood cells (glutathione peroxidase activity was higher in females). Cholesterol feeding was associated with opposing effects on the activity of plasma glutathione peroxidase (increased in males but decreased in females). Evidence was also found for complex sex- and tissue-related differences in patterns of ageing over the nine-week experimental period. CONCLUSIONS: Although sex-related differences in antioxidant enzyme profiles are demonstrable in aortic tissues and blood of Japanese quail fed control or cholesterol-supplemented diets, it seems unlikely that these are of sufficient magnitude to account for the large difference in susceptibility to atherosclerosis between males and females. The complex sex- and tissue-dependent effects of ageing on the activities of antioxidant enzymes observed emphasize the importance of age- and sex-matched controls in experimental studies of antioxidant enzyme alterations in disease processes generally.

Antioxidant status of Japanese quail: comparison of atherosclerosis-susceptible and -resistant strains.

OBJECTIVE: To compare levels of antioxidant components of blood and aortic tissue from two strains of Japanese quail showing high and low susceptibilities to atherosclerosis and receiving either control or cholesterol-enriched diets. ANIMALS: All experimental birds were placed on the control diet until eight weeks of age. Twenty males of each strain were then placed on the atherogenic diet (control diet supplemented with 1% cholesterol) and another 20 males of each strain were continued on the control diet for an additional 10 weeks. MAIN RESULTS: In the absence of cholesterol supplementation, plasma cholesterol and triglyceride and antioxidant enzyme profiles of aorta, red blood cells and plasma were comparable in the two groups of birds, with the exception of a small, but significant (P < 0.05), decrease in aortic glutathione reductase in susceptible animals (0.378 nmol/min/mg) relative to the resistant birds (0.441 nmol/min/mg). Cholesterol feeding produced larger increases in cholesterol and triglycerides and more extensive atherosclerotic plaque formation in susceptible compared with resistant quail. In the susceptible group, significant negative correlations were noted between severity of atherosclerotic lesions and aortic superoxide dismutase (correlation coefficient -0.752) and glutathione reductase (correlation coefficient -0.775) activities. Cholesterol feeding was associated with increased activity of plasma glutathione peroxidase and superoxide dismutase activities in both strains, although only the susceptible birds showed significant positive correlations of superoxide dismutase activities with plasma cholesterol (correlation coefficient +0.694) and triglycerides (correlation coefficient +0.669). Peroxide-induced depletion of glutathione in red blood cells was unaffected by cholesterol feeding, although red blood cell susceptibility to lipid peroxidation was decreased to an equivalent degree in both strains. CONCLUSIONS: Susceptible and resistant quail are biochemically distinct in terms of alterations in antioxidant components produced by dietary cholesterol supplementation. Results of the present study are consistent with the proposed involvement of oxidative processes in the pathogenesis of atherosclerosis.

Effects of various anesthetic regimens on tissue antioxidant enzyme activities.

It has been suggested that oxidative processes are involved in a variety of pathological conditions, notably ischemia-reperfusion injury. Moreover, anesthetics appear to exert differential effects on the severity of such injury, these being unlikely wholly attributable to their differential effects on cardiovascular or microcirculatory status. It is possible that these variable effects of anesthetics on this type of injury may be due, at least in part, to changes in the production of free radicals and/or in their detoxification by endogenous antioxidant enzymes. We have attempted to explore the latter possibility by measuring activities of catalase, superoxide dismutase (SOD), glutathione peroxidase (GPX) and glutathione reductase in normal heart tissue and red cells obtained from rats anesthetized using a variety of agents (CO2, halothane, pentobarbital or ether). For comparison, analyses were also performed on tissues from unanesthetized animals rendered unconscious by stunning prior to sacrifice. Results indicated that myocardial SOD activity was significantly greater in halothane-anesthetized as compared with CO2-anesthetized animals. Red cell SOD activities did not show such differences. However, red cell GPX activity was found to be greater in halothane-anesthetized than in pentobarbital-anesthetized rats. In general, however, antioxidant enzyme activities measured ex vivo were minimally affected by the use of anesthetics prior to euthanasia. Our findings, therefore, do not support the proposal that the influence of anesthetics on the course of ischemia-reperfusion injury involves effects at the level of enzymatic antioxidant components.

Babesiosis in Washington State: a new species of Babesia?

OBJECTIVE: To characterize the etiologic agent (WA1) of the first reported case of babesiosis acquired in Washington State. DESIGN: Case report, and serologic, molecular, and epizootiologic studies. SETTING: South-central Washington State. PATIENT: A 41-year-old immunocompetent man with an intact spleen who developed a moderately severe case of babesiosis. MEASUREMENTS: Serum specimens from the patient were assayed by indirect immunofluorescent antibody (IFA) testing for reactivity with seven Babesia species and with WA1, which was propagated in hamsters inoculated with his blood. A Babesia-specific, ribosomal-DNA (rDNA) probe was hybridized to Southern blots of restriction-endonuclease-digested preparations of DNA from WA1, Babesia microti, and Babesia gibsoni. Serum specimens from 83 family members and neighbors were assayed for IFA reactivity with WA1 and B. microti. Small mammals and ticks were examined for Babesia infection. RESULTS: The patient's serum had very strong IFA reactivity with WA1, strong reactivity with B. gibsoni (which infects dogs), but only weak reactivity with B. microti. DNA hybridization patterns with the rDNA probe clearly differentiated WA1 from B. gibsoni and B. microti. Four of the patient's neighbors had IFA titers to WA1 of 256. The tick vector and animal reservoir of WA1 have not yet been identified, despite trapping 83 mammals and collecting 235 ticks. CONCLUSIONS: WA1 is morphologically indistinguishable but antigenically and genotypically distinct from B. microti. Some patients elsewhere who were assumed to have been infected with B. microti may have been infected with WA1. Improved serodiagnostic and molecular techniques are needed for characterizing Babesia species and elucidating the epidemiology of babesiosis, an emergent zoonosis.

Species-related variations in tissue antioxidant status--I. Differences in antioxidant enzyme profiles.

1. Antioxidant enzyme activity profiles in red cells of man, rabbit, quail, pig and rat have been investigated and found to exhibit striking differences. 2. No direct correlations between activities of "functionally coupled" enzymes (superoxide dismutase/catalase and glutathione peroxidase/glutathione reductase) were apparent, suggesting their independent regulation. 3. However, activities of red cell catalase and glutathione peroxidase in the various species studied were inversely correlated. 4. This was most evident in quail red cells, which showed negligible catalase activity but the highest levels of glutathione peroxidase of all the species examined. 5. A significant positive correlation between catalase and glutathione reductase activities was also demonstrated. 6. This may be relevant to the suggestion that the binding of NADPH to catalase may serve to decrease the intracellular inactivation of this reducing cofactor which may be limiting in the glutathione reductase reaction. 7. Basal levels of glutathione, which have been claimed to be limiting for the glutathione peroxidase reaction, were found to correlate positively with the activity of this enzyme in red cells. 8. Myocardial tissues also exhibited species-related differences in antioxidant enzyme profiles but these did not bear any obvious relationship to patterns observed in the corresponding red cells.

Species-related variations in tissue antioxidant status--II. Differences in susceptibility to oxidative challenge.

1. In order to investigate possible species-related variations in antioxidant capacity, the susceptibility of red cells from various species (e.g. rat, rabbit, pig and quail) to depletion of glutathione (GSH) and formation of malondialdehyde (MDA), an indirect measure of lipid peroxidation, following in vitro oxidative challenge with t-butylhydroperoxide (tBHP) has been examined. 2. Marked differences in sensitivity were found, although the relative order of susceptibilities varied depending on the index of oxidation used. 3. For example, pig erythrocytes showed the highest sensitivity to depletion of GSH but the greatest resistance to tBHP-induced MDA formation. 4. Red cell susceptibility to oxidative stress under the experimental conditions used was not predictable from basal levels of GSH or from the activities of antioxidant enzymes, suggesting a prominent role of non-enzymatic antioxidants. 5. Species-dependent differences in antioxidant capacity were also found to extend to myocardial tissue homogenates and some degree of parallelism was noted with tBHP-induced MDA formation in red cells of the same species. 6. Thus, the relative resistance of both tissues from pig contrasted with the high susceptibility of red cells and myocardium from rat and quail. 7. This parallelism allows the suggestion that the functional consequences of antioxidant interventions might be discernible from measurements involving red cells. 8. Our findings may have potentially important implications in the interpretation and comparison of data obtained with experimental models of disease states in which oxidative processes are implicated when differences in species are involved.

Altered antioxidant status in ischemic/reperfused rabbit myocardium: reperfusion time-course study.

A progressive impairment in antioxidant status of rabbit hearts was observed when a fixed period (40 mins) of ischemia produced by coronary artery ligation was followed by increasing periods of reperfusion. This was reflected in a reduction in myocardial glutathione levels and an increase in glutathione depletion and production of thiobarbituric acid-reactive substances following in vitro oxidative challenge with t-butylhydroperoxide. Correlation analysis, in which activities of antioxidant enzymes were viewed in relation to biochemical indices of antioxidant status, indicated the functionally relevant suppression of Cu,Zn-superoxide dismutase and glutathione reductase activities in ischemic/reperfused tissues. These results and the demonstration of significant decreases in the activity of glutathione-dependent antioxidant enzymes under acidotic conditions suggest that transient impairment in the functioning of antioxidant enzymes may be involved in the triggering of irreversible myocardial ischemia-reperfusion injury.

Altered antioxidant status in the ischemic/reperfused rabbit myocardium: effects of allopurinol.

In the rabbit myocardium, ischemia (produced by ligation of the left circumflex coronary artery) is associated with a reduction in antioxidant capacity. This is reflected by an increased glutathione depletion and production of thiobarbituric acid reactive substances following in vitro oxidative challenge with t-butylhydroperoxide. This effect is greatly intensified by reperfusion following periods of ischemia longer than 20 mins, thereby paralleling the onset of irreversible injury. Chronic allopurinol pretreatment (1 mg/mL in drinking water or approximately 75 mg/kg/day for seven days prior to ligation) provides significant protection of the ischemic/reperfused myocardium to t-butylhydroperoxide induced glutathione depletion and production of thiobarbituric acid reactive substances. This protection was not associated with any significant alterations in levels of tissue ATP or in the activities of the myocardial antioxidant enzymes catalase, copper,zinc-superoxide dismutase or glutathione peroxidase, suggesting that allopurinol may exert its effects by direct radical scavenging or by some other mechanism unrelated to xanthine oxidase inhibition.

Antioxidant enzyme alterations in experimental and clinical diabetes.

Previous studies from our laboratory have demonstrated the presence of complex alterations in the activities of antioxidant enzymes in various tissues of rats with streptozotocin (STZ)-induced diabetes. In the present investigation, it is shown that rats made diabetic with alloxan (ALX), an agent differing from STZ both chemically and in its mechanism of diabetogenesis, show virtually identical tissue antioxidant enzyme changes which, as is the case with STZ, are preventable by insulin treatment. The finding that the patterns of antioxidant enzyme alterations in chemically-induced diabetes are independent of the diabetogenic agent used and the presence of similar abnormalities in tissues of spontaneously diabetic (BB) Wistar rats (particularly when diabetic control is less than optimal) suggest that the changes observed are a characteristic feature of the uncontrolled diabetic state and that these may be responsible for (or predispose to) the development of secondary complications in clinical diabetes. Comparative studies involving red cells of diabetic rats and human diabetics revealed a number of common changes, namely an increase in glutathione reductase activity, a decreased susceptibility to oxidative glutathione depletion (which was related to the presence of hyperglycemia) and an increased production of malondialdehyde (an indirect index of lipid peroxidation) in response to in vitro challenge with hydrogen peroxide. In the diabetic patients, the extent of this increase in susceptibility of red cell lipids to oxidation paralleled the severity of diabetic complications. Our results suggest that increased (or uncontrolled) oxidative activity may play an important role in the pathogenesis of complications associated with the chronic diabetic state.

Erythrocyte abnormalities in a hypoalphalipoproteinemia syndrome resembling fish eye disease.

Erythrocyte membrane (EM) abnormalities in a 16-yr-old boy with hypoalphalipoproteinemia resembling fish eye disease (FED-LS) were investigated. The proband's erythrocytes had markedly decreased osmotic fragility with target cells observed in the peripheral film. Analysis of his EM lipids revealed normal cholesterol and phospholipid content but a marked increase in phosphatidylcholine with concomitant decreases in phosphatidylethanolamine and sphingomyelin. Of the EM enzymes examined, acetylcholinesterase and superoxide dismutase activities were decreased while those of Na+-K+ ATPase, catalase and glutathione reductase were normal. 51Cr erythrocyte survival in the patient was slightly decreased. The observed changes in a number of structural and functional properties of erythrocytes in this disorder are indistinguishable from those previously described in homozygotes for familial lecithin:cholesterol acyltransferase (LCAT) deficiency. Thus, it is possible that in both of these disorders an abnormality of plasma LCAT activity causes, either directly or indirectly, functional and structural changes in the erythrocyte membrane.

In vivo and in vitro studies of bacterial endotoxin-membrane interactions and the effects of membrane-active agents.

The characteristics of 51Cr-labelled E. coli endotoxin binding to human erythrocyte membranes in vitro have been investigated. A saturable component of binding was apparent at low endotoxin concentrations (less than 50 micrograms ml-1) relevant to its in vivo actions, while at higher concentrations binding was non-saturable and increased in linear fashion. Experiments examining the ability of unlabelled endotoxin to antagonize the binding of labelled toxin provided further evidence for these specific and non-specific modes of endotoxin-membrane interaction. Membrane-active agents previously shown to reduce endotoxin toxicity in vivo decreased endotoxin binding to erythrocyte membranes in vitro, with propranolol and pranolium being the most effective in this regard. Tissue distribution studies following administration of radiolabelled endotoxin to guinea-pigs showed a positive correlation between the accumulation of 51Cr-endotoxin in lung and elevations in plasma acid phosphatase activity, a measure of in vivo endotoxin toxicity. The in vivo accumulation of 51Cr-endotoxin in guinea-pig lung was reduced by prior treatment with (+)-propranolol or pranolium, paralleling the results of the in vitro binding studies. Our results suggest that membrane-active agents such as (+)-propranolol may be useful adjuncts to antimicrobial drugs in the therapy of gram-negative endotoxaemia.

Studies on the interaction of Escherichia coli endotoxin with erythrocyte membranes.

Escherichia coli lipopolysaccharide (endotoxin) alters the stability of erythrocytes to hypotonic lysis although the nature and magnitude of the effect varied with temperature and with the type of red blood cell examined. Evidence has been obtained suggesting a possible modulatory role of membrane lipids in governing the molecular consequences of membrane-endotoxin interaction. The marked effect of temperature on the stabilization of red cells by endotoxin was not attributable to variations in toxin binding and was not observed with more conventional structurally unrelated antihemolytic agents. Although chemical modifications which alter the toxicity of endotoxin in vivo also modify its ability to stabilize erythrocytes in vitro, no simple relationship between in vivo endotoxin toxicity and in vitro effects on erythrocyte stability was apparent. The critical dependence of endotoxin antihemolytic effects in vitro on molecular structure may offer a convenient means of assessing the homogeneity of these preparations before performing experiments in vivo.

Acetylcholinesterase: a probe for the study of antiarrhythmic drug-membrane interactions.

Structural consequences of antiarrhythmic drug interaction with erythrocyte membranes were analyzed in terms of resulting changes in the activity of membrane-associated acetylcholinesterase. When enzyme inhibitory effects of drugs were compared at concentrations producing an equivalent degree of erythrocyte antihemolysis, a number of distinct groupings emerged, indicating that the molecular consequences of drug-membrane interaction are not identical for all agents examined. Differences in drug-induced acetylcholinesterase inhibition in intact erythrocytes, erythrocyte membranes and a brain synaptic membrane preparation emphaized the role of membrane structural organization in determining the functional consequences of antiarrhythmic interaction in any given system. While the inhibitory actions of lidocaine, D-600 and bretylium in intact red cells were not altered by an increased transmembrane chloride gradient, enhanced enzyme inhibition by quinidine and propranolol was observed under these conditions. The diverse perturbational actions of these membrane-stabilizing antiarrhythmics observed here may be indicative of a corresponding degree of complexity in the mechanisms whereby substances modify the potential-dependent properties of excitable tissues.