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Biomedical subjects

W Kübler

Publications and source records attributed to W Kübler.

At least 163 records · Page 9Linked to original sources
PubMed1995

Development and characterization of a rapid assay for bedside determinations of cardiac troponin T.

BACKGROUND: The appearance of cardiac proteins in blood is the most specific and sensitive indicator of acute myocardial cell necrosis. The measurement of cardiac markers, however, is time consuming and requires sophisticated equipment. To facilitate the biochemical detection for acute myocardial cell necrosis, a whole-blood rapid assay device for cardiac troponin T detection was developed that provides a test result within 20 minutes. METHODS AND RESULTS: Monoclonal antibody M7 is labeled with gold particles, and antibody 1B10 is labeled with biotin. Both antibodies, as well as buffer substances and detergents, are adsorbed onto paper fleeces mounted below an application well. Heparinized blood (160 microL) applied to this well solubilizes the dry chemistry reagents. Blood cells are separated from plasma via a glass-fiber fleece. The immunocomplexes formed are concentrated within the reading zone by binding of the biotin-labeled antibody with streptavidine immobilized to the test device. Troponin T bound to the test device serves as a control. The detection limit of this assay is 0.18 microgram/L with a cross-reactivity with skeletal troponin T of 0.5%. In clinical analyses involving 25 healthy volunteers, 62 patients with chest pain but without myocardial ischemia, 35 patients with acute myocardial infarction, 24 patients with minor myocardial cell damage due to radiofrequency ablation, and 35 patients with unstable angina, the rapid assay was comparable to the troponin T enzyme immunoassay in regard to sensitivity and specificity. CONCLUSIONS: This newly developed assay allows accurate, rapid, and convenient diagnosis of acute myocardial cell necrosis.

Angina, Unstable↗
PubMed1995

Impact of intensive physical exercise and low-fat diet on collateral vessel formation in stable angina pectoris and angiographically confirmed coronary artery disease.

This randomized study was performed to assess the effects of > 3 hours of physical exercise per week and low-fat diet on collateral formation in nonselected patients with coronary artery disease (intervention group, n = 56). Results were compared with those of patients in a control group (n = 57), who received usual care by their private physicians. Coronary lesions were assessed by quantitative coronary angiography at the beginning and after 1 year of study (n = 92). As previously reported, after 1 year there was a significant retardation of progression of coronary artery disease in the intervention group as compared with the control group. In this study, evaluation of collateral formation revealed no significant difference between both groups, and changes in hemodynamic and metabolic variables or leisure time physical activity were not related to changes in collateral formation. Although progression of the disease was significantly related to an increase in collateral formation, regression was significantly related to a decrease in collateral formation (p < 0.00001). Because patients in the intervention group exercised for > 3 hours/week, and patients with regression of coronary artery disease even dedicated 5 to 6 hours to leisure time physical activity per week, these findings question whether an exercise program within the safety tolerance of patients will be able to induce coronary collateralization in the presence of regression of coronary artery disease.

Activities of Daily Living↗
PubMed1995

Low-dose radioactive endovascular stents prevent smooth muscle cell proliferation and neointimal hyperplasia in rabbits.

BACKGROUND: Restenosis induced by smooth muscle cell (SMC) migration and proliferation and neointimal thickening limits the clinical success of balloon angioplasty and stent implantation. In this study, the long-term effect of endovascular irradiation via low-dose radioactive stents on neointima formation was compared with conventional stent implantation in a rabbit model. METHODS AND RESULTS: Palmaz-Schatz stents were made radioactive in a cyclotron. The stents had a very low activity (maximum, 35 microCi), and thus, manipulation did not require extensive radiation protection. One, 4, 12, and 52 weeks after the implantation of nonradioactive stents and radioactive stents in rabbit iliac arteries, neointimal thickening was analyzed by quantitative histomorphometry. Immunostaining for endothelial cell von Willebrand factor, macrophages, SMC alpha-actin, collagen type I, and proliferating cell nuclear antigen (PCNA) was performed to determine radiation-induced changes in the arterial wall. SMC proliferation was quantified by computer-assisted cell counting of PCNA-immunoreactive cells. Neointima formation was markedly suppressed by the implantation of radioactive stents in a dose-dependent fashion at all observed time points. At peak proliferative activity of SMCs 1 week after nonradioactive stent implantation, 30 +/- 2% of SMCs in the neointima were proliferating, compared with 0.5 +/- 0.1% of SMCs after implantation of stents with an initial activity of 35 microCi (P < .001). The neointima covering radioactive stents was characterized by decreased smooth muscle cellularity and increased extracellular matrix formation. Further, we observed a delayed endothelialization depending on the radiation dose. No difference in vascular thrombosis was found after nonradioactive and radioactive stent implantation. CONCLUSIONS: The results of this study clearly indicate that low-dose radioactive endovascular stents potently inhibit SMC proliferation and neointimal hyperplasia in rabbits.

Animals↗
PubMed1995

X-linked dilated cardiomyopathy. Novel mutation of the dystrophin gene.

We report on a family with a severe form of X-linked dilated cardiomyopathy (DCM). Two brothers, the elder requiring heart transplantation, and a maternal cousin presented elevated creatine kinase levels, increased right ventricular diameters and electrocardiographic abnormalities. All complained of exertional cramping myalgia, but none had muscle weakness or a pathological electromyogram. Muscle biopsies of these individuals revealed a mild myopathic picture with atrophic type I and hypertrophic type II fibers. Immunofluorescence using N- and C-terminal antibodies (dys-2, dys-3) against the dystrophin protein showed preserved, but reduced intensity of staining of the sarcolemmal membranes. Using the same two antibodies, Western blot analyses revealed a dystrophin molecule of the expected molecular weight, which was quantitatively reduced by 80%. However, the dys-1 antibody, directed against the mid rod region of the dystrophin protein, did not react with dystrophin both on Western blot and immunofluorescence. Linkage analysis with polymorphic markers of the dystrophin gene revealed an identical haplotype at the 5' region in all affected individuals (two point lod score of 1.93, phi = 0). A deletion of exons 48, 45-53, 2-7 and 1 including the promoter region of the dystrophin gene, as described in rare cases with similar clinical signs could be excluded by multiplex PCR and Southern blot analyses of this DCM family. In addition, a major splice-mutation of dystrophin mRNA was excluded by RT-PCR of skeletal and heart muscle tissue. Therefore, we conclude that a novel mutation in the 5' region of the dystrophin gene phenotypically leads to this severe form of DCM. Extensive analyses of the dystrophin gene, in particular of the sequences coding for the antigenic determinants of the dys-1 antibody in the mid rod region, may identify the molecular cause of this monogenetic form of DCM.

Adult↗
PubMed1995

Residual 201Tl activity in irreversible defects as a marker of myocardial viability. Clinicopathological study.

BACKGROUND: The objective of the present study was to characterize the relation between the residual 201Tl activity in irreversible perfusion defects and the extent of irreversible myocardial damage indicated by the volume fraction of myocardial interstitial fibrosis in patients with chronic coronary artery disease. METHODS AND RESULTS: Stress planar 201Tl scintigraphy with tracer reinjection at rest was performed in 37 patients with > or = 75% stenosis of the left anterior descending coronary artery, and anteroseptal 201Tl activity was quantified by computer-assisted placement of regions of interest from the serial myocardial images. During coronary artery bypass grafting (performed within 6 +/- 3 weeks after scintigraphy), two transmural biopsy specimens were taken from the anterior wall of the left ventricle and the amount of interstitial fibrosis was assessed by use of light microscopic morphometry. A wide spectrum of interstitial fibrosis was obtained, ranging from 15 vol% to 60 vol%. Interstitial fibrosis was similar in patients with reversible (n = 11) or irreversible (n = 15) tracer defects in conventional stress-redistribution images. However, interstitial fibrosis was significantly lower in patients who had enhanced regional 201Tl activity after tracer reinjection compared with those who did not have enhancement of tracer activity after reinjection (28 +/- 8 vol%, n = 7, versus 41 +/- 12 vol%, n = 8; P = .031). The correlation between relative poststenotic 201Tl activity and interstitial fibrosis after tracer reinjection was significantly improved compared with conventional redistribution images (r = -.622 versus r = -.851, n = 15; P < .01). CONCLUSIONS: The present data demonstrate that the level of regional 201Tl activity in redistribution and, in particular, reinjection images is significantly related to the mass of preserved viable myocytes in poststenotic left ventricular myocardium. Therefore, the residual 201Tl activity provides information about viability within irreversible perfusion defects and may itself serve as marker of myocardial viability.

Biopsy↗
PubMed1995

Electropharmacology of the bradycardic agents alinidine and zatebradine (UL-FS 49) in a conscious canine ventricular arrhythmia model of permanent coronary artery occlusion.

Myocardial infarction was produced in 27 anesthetized dogs by ligating the left anterior descending (LAD) coronary artery proximal to the septal branch. Nineteen of these animals survived the operation and were studied by programmed stimulation in a random sequence between the third and seventh days after the infarct. Complete electrophysiologic testing was implemented in each animal prior to and after single doses of either alinidine (1 mg/kg IV) or zatebradine (0.5 mg/kg IV). Alinidine prevented reinduction of sustained ventricular tachycardia (SVT) in only 2 of 9 dogs and zatebradine in 1 of 8 dogs. The SVT cycle length was not significantly changed in all cases in which it was still inducible despite drug administration (p > 0.05). Alinidine lengthened the effective refractory period (ERP) in the AV node (p < 0.01), whereas zatebradine did not induce a statistically significant prolongation. Conversely, zatebradine increased the left ventricular ERP, while alinidine left it almost unchanged. The rate-corrected QT interval (QTc) did not significantly differ from control values after the administration of either agents. Also, the duration and the ERP of infarctzone potentials, defined as late potentials, remained unaltered. The results indicate that the bradycardic agents alinidine and zatebradine do not exert antiarrhythmic efficacy against SVT induced during subacute myocardial infarction in conscious dogs. None of these drugs substantially changed ventricular electrophysiology or showed a drug-specific proarrhythmic effect.

Animals↗
PubMed1995

Intracellular compartmentation of troponin T: release kinetics after global ischemia and calcium paradox in the isolated perfused rat heart.

The marked differences in troponin T serum concentrations observed in patients with reperfused and non-reperfused myocardial infarction may be due to a perfusion dependent wash-out of an unbound fraction of cardiac troponin T. To test the release kinetics of troponin T experimentally, the isolated rat heart (Langendorff preparation) was damaged either by the calcium paradox or by no-flow ischemia. Following membrane damage by the calcium paradox troponin T (TNT) showed the same release kinetics in the coronary effluent as the cytosolic markers creatine kinase (CK) or lactate dehydrogenase (LDH). Peak levels of troponin T (282 +/- 58 micrograms/l), CK (6754 +/- 1642 U/l), and LDH (5817 +/- 1730 U/l) occurred 5 min after onset of reperfusion with calcium containing buffers and returned to 9.9%, 1.3%, and 1% of their respective peak levels within 55 min of reperfusion. During reperfusion after no-flow ischemia different release kinetics were found for cytosolic enzymes and troponin T. After 60 min of ischemia, troponin T levels in the coronary effluent increased over the entire reperfusion period of 55 min, almost doubling the 5 min value (191%). In contrast, cardiac enzymes rapidly declined to 18% (CK) and 23% (LDH) of their respective 5 min values at the end of reperfusion. Light microscopy after reperfusion with carbon black revealed a complete and homogeneous reperfusion of Langendorff hearts after no-flow ischemia. Immunoblot analysis confirmed the release of an undegraded 39 kDa troponin T molecule, both after global ischemia and the calcium paradox. These data indicate that prolonged ischemia induces a continuous liberation of cardiac troponin T, most probably from disintegrating myofibres, whereas membrane damage leads almost exclusively to leakage of a functionally unbound troponin T pool. These findings may explain the biphasic serum concentration changes of cardiac troponin T in patients with reperfused myocardial infarction.

Animals↗
PubMed1995

An epidemiologic study of food consumption habits in Germany.

Food consumption habits were studied in subgroups of subjects in the German Nutrition Survey (Nationale Verzehrstudie [NVS]) on the basis of body weight. Our study was performed in an 18- to 88-year-old representative subgroup of 2,006 noninstitutionalized volunteers with no significant pathology (known as the Verbundstudie, Ernährungserhebung, and Risikofaktorenanalytik [VERA] subgroup). Using the German Food Code, food and nutrient intakes were calculated from 7-day dietary records. A stratification analysis was used to determine significant differences in food consumption habits of overweight subjects in comparison to normal-weight subjects. The results showed an increase in the prevalence of overweight (body mass index [BMI], 25 to 30) with age, from 15% in the group aged 18 to 24 years to 50% in the group aged more than 55 years. The prevalence of severe overweight (BMI, 30 to 40) increased from 3% to 17% in the same age groups, whereas morbid obesity (BMI, > 40) was found in only 0.4% of the study population. The calculated daily energy intake showed only a very weak correlation with BMI, probably because individual energy requirements and expenditures were not taken into account. However, differences were found between BMI subgroups in terms of the types of food consumed: a high BMI was associated with a higher consumption of meat and meat products but a lower consumption of milk and dairy products and bread and other cereal-based foods.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1995

Physical training in patients with stable chronic heart failure: effects on cardiorespiratory fitness and ultrastructural abnormalities of leg muscles.

OBJECTIVES: The present study was designed to evaluate the effect of an ambulatory training program on ultrastructural morphology and the oxidative capacity of skeletal muscle and its relation to central and peripheral hemodynamic variables in patients with chronic heart failure. BACKGROUND: Clinical evidence supports the hypothesis that exercise intolerance in patients with chronic heart failure is not only a consequence of low cardiac output, but is also a result of alterations in oxidative metabolism of skeletal muscle. METHODS: Twenty-two patients were prospectively randomized either to a training group (mean [+/-SD] ejection fraction 26 +/- 9%, n = 12) participating in an ambulatory training program or to a physically inactive control group (ejection fraction 27 +/- 10%, n = 10). At baseline and after 6 months, patients underwent symptom-limited bicycle exercise testing, and central and peripheral hemodynamic variables were measured. Percutaneous needle biopsy samples of the vastus lateralis muscle were obtained at baseline and after 6 months. The ultrastructure of skeletal muscle was analyzed by ultrastructural morphometry. RESULTS: After 6 months, patients in the training group achieved an increase in oxygen uptake at the ventilatory threshold of 23% (from 0.86 +/- 0.2 to 1.07 +/- 0.2 liters/min, p < 0.01 vs. control group) and at peak exercise of 31% (from 1.49 +/- 0.4 to 1.95 +/- 0.4 liters/min, p < 0.01 vs. control group). There was no significant change in oxygen uptake at the ventilatory threshold and at peak exercise in the control group. The total volume density of mitochondria and volume density of cytochrome c oxidase-positive mitochondria increased significantly by 19% (from 4.7 +/- 1.5 to 5.6 +/- 1.5 vol%, p < 0.05 vs. control group) and by 41% (from 2.2 +/- 1.0 to 3.1 +/- 1.0 vol%, p < 0.05 vs. control group) after 6 months of regular physical exercise. Cardiac output at rest and at submaximal exercise remained unchanged but increased during maximal symptom-limited exercise from 11.9 +/- 4.0 to 14.1 +/- 3.3 liters/min in the training group (p < 0.05 vs. baseline; p = NS vs. control group). Peak leg oxygen consumption increased significantly by 45% (from 510 +/- 172 to 740 +/- 254 ml/min, p < 0.01 vs. control group). Changes in cytochrome c oxidase-positive mitochondria were significantly related to changes in oxygen uptake at the ventilatory threshold (r = 0.82, p < 0.0001) and at peak exercise (r = 0.87, p < 0.0001). CONCLUSIONS: Regular physical training increases maximal exercise tolerance and delays anaerobic metabolism during submaximal exercise in patients with stable chronic heart failure. Improved functional capacity is closely linked to an exercise-induced increase in the oxidative capacity of skeletal muscle.

Biopsy↗
PubMed1995

Nicotine-induced exocytotic norepinephrine release in guinea-pig heart, human atrium and bovine adrenal chromaffin cells: modulation by single components of ischaemia.

The influence of single components of myocardial ischaemia, such as anoxia, substrate withdrawal, hyperkalemia and extracellular acidosis, on nicotine-induced norepinephrine (NE) release was investigated in the isolated perfused guinea-pig heart, in incubated human atrial tissue and in cultured bovine adrenal chromaffin cells (BCC). In normoxia, nicotine (1-1000 mumol/l) evoked a concentration-dependent release of NE (determined by high pressure liquid chromatography and electrochemical detection) from guinea-pig heart and human atrium. In contrast to selective anoxia (Po2 < 5 mmHg) or glucose withdrawal, respectively, anoxia in combination with glucose withdrawal (5-40 min) markedly potentiated nicotine-induced NE release both in guinea-pig heart and human atrium. The sensitization of cardiac sympathetic nerve endings to nicotine was characterized by a lower threshold concentration and an approximate two-fold increase of maximum NE release, peaking after 10 min of anoxia and glucose withdrawal. Cyanide intoxication (1 mmol/l) combined with glucose withdrawal resulted in a similar increase of nicotine-induced sympathetic transmitter release both in guinea-pig heart and human atrium. In contrast, the nicotine-induced (10 mumol/l) NE overflow was only slightly potentiated by 10 min of global ischaemia in guinea-pig heart. Both hyperkalemia ([K+] 16 mmol/l) and acidosis (pH 6.8-6.0) distinctly attenuated the stimulatory effect of nicotine in guinea-pig heart and human atrium under normoxic conditions. Consistent with an exocytotic release mechanism, NE release was dependent on the presence of extracellular calcium under all conditions tested. Furthermore, NE overflow from guinea-pig heart was accompanied by a release of the exocytosis marker neuropeptide Y (NPY; determined by radioimmunoassay). In BCC, nicotine (1-10 mumol/l) evoked a release of NE and NPY and a transient rise of [Ca2+]i (determined with fura-2) during normoxia which were both dependent on the presence of extracellular calcium. Both hyperkalemia and acidosis markedly reduced the exocytotic release of sympathetic transmitters and the corresponding [Ca2+]i-transients. These data demonstrate that nicotine-induced cardiac exocytotic NE release is markedly potentiated during short-term anoxia in combination with glucose withdrawal. In contrast, a brief period of ischaemia causes only a slight sensitization of cardiac sympathetic nerve endings to nicotine. This discrepancy may be due to an attentuation of nicotine-evoked NE release by hyperkalemia and by acidosis. The protective effect of these factors against anoxia-induced sensitization to nicotine appears to be related to the inhibition of nicotine-evoked [Ca2+]i-transients.

Adrenal Medulla↗
PubMed1995

Effect of an acute beta-adrenergic blockade on the relationship between ventilatory and plasma lactate threshold.

The present study assesses interobserver variability and day-to-day reproducibility of ventilatory threshold T(ven) and lactate threshold T(lac) in healthy young men. The data were obtained before and after acute beta-adrenergic blockade with metoprolol (100 mg/d p.o.). Fifteen healthy young men underwent progressively increased treadmill ergometry tests on two separate days (day 1, 2). Ten out of fifteen subjects participated in a third exercise test under an acute beta-adrenergic blockade (day 3). Interobserver variability of oxygen uptake at T(ven) (8%; +/- 0.136 l/min) and T(lac) (5%; +/- 0.984 l/min) was small and day-to-day reproducibility of T(ven) (7%; +/- 0.131 l/min) and T(lac) (7%; +/- 0.133 l/min) high. Under acute beta-adrenergic blockade T(ven) occurred at a significantly lower work load (360 +/- 117 s) as compared with T(ven) of days 1 and 2 (477 +/- 153 s; p < 0.05), and T(lac) of day 3 after beta-adrenergic blockade (456 +/- 76 s; p < 0.05). Therefore, a significantly lower oxygen uptake (1.409 +/- 0.29 l/min) could be observed at T(ven) of day 3 as compared with T(ven) of days 1 and 2 (1.852 +/- 0.30; p < 0.001), and T(lac) of days 1 and 2 (1.724 +/- 0.22; p < 0.001). There was a significant linear correlation between oxygen uptake at T(ven) and T(lac) before beta-adrenergic blockade (r = 0.86; p < 0.001). This correlation, however, was lost following an acute beta-adrenergic blockade (r = 0.56; n.s.).(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Antagonists↗
PubMed1995

Preservation of myocardial blood flow by calcium antagonists does not prevent attenuation of regional myocardial function after repetitive brief periods of myocardial ischaemia in the rat heart.

The aim of this study was to assess the effect of two different calcium channel blockers on myocardial blood flow and function in a rat model of myocardial 'stunning' by repeated short episodes of ischaemia ('repetitive ischaemia'). In an open chest rat model, the left anterior descending coronary artery was ligated for 10 min followed by 15 min reperfusion. In total, five periods of ischaemia and reperfusion were performed. Myocardial blood flow was assessed by the hydrogen clearance technique and systolic thickening fraction by pulsed Doppler. After five episodes of ischaemia, myocardial blood flow adn myocardial thickening in the ischaemic area were reduced by 60 +/- 8% and 52 +/- 7% (n=9), respectively, as compared to baseline. Continuous intravenous infusion of the calcium channel blockers nifedipine (n=6) and gallopamil (n=6), started 20 min prior to onset of ischaemia, attenuated the ischaemia-induced decrease of myocardial perfusion. Nifedipine was the most effective with only 5 +/- 2% reduction in blood flow after five ischaemic episodes, whereas reduction of myocardial blood flow was 30 +/- 4% in the presence of gallopamil. However, neither nifedipine nor gallopamil were able to prevent regional ventricular dysfunction induced by repetitive ischaemia. Despite the preservation of myocardial blood flow following repetitive ischaemia, calcium channel blockers do not prevent ischaemia-induced reduction of myocardial function in the ischaemic area.

Animals↗
PubMed1995

Refractory oedema in congestive heart failure: a contributory role of loop diuretics?

We report a patient with congestive heart failure (CHF) who presented with massive oedema resistant to therapy with maximal doses of loop diuretics, despite an adequate renal function. After a diuretic pause and dietary salt restriction, a conventional dose of furosemide in combination with distally active diuretics induced a prompt weight loss exceeding 30 kg with stable renal function. We suggest that the 'refractory' oedema in this patient was due to a combination of CHF and inappropriate (loop) diuretic therapy in conjunction with a high dietary sodium intake. We conclude that in the absence of hyponatremia and renal failure, even severe oedema may not represent a negative prognostic indicator. The recognition of diuretic-associated mechanisms complicating cardiac oedema is essential to avoid the vicious circle of worsening oedema whilst escalating therapy with loop diuretics.

Adult↗
PubMed1995

Interaction of vitamins with mental performance.

In the presence of a chronically insufficient vitamin supply which was verified by repeated measurements of the vitamin parameters, many unfavorable psychometric findings in the corresponding deficiency groups are observed for the vitamins C, thiamin, riboflavin, cobalamin and folate, depending on the degree of the insufficient vitamin supply. Vitamin supplementation in cases of initially insufficient vitamin supply indicate some effects in the sense of an improvement of behavior and cognitive functions. Supplemental vitamin intake in physiological dosages in addition to a vitamin-sufficient diet did not lead to an improvement of behavior and mental performance.

Adolescent↗
PubMed1995

Impaired function of inhibitory G proteins during acute myocardial ischemia of canine hearts and its reversal during reperfusion and a second period of ischemia. Possible implications for the protective mechanism of ischemic preconditioning.

A brief antecedent period of myocardial ischemia and reperfusion can delay cellular injury during a subsequent ischemic condition. Recent observations suggest that this protective mechanism depends on the continued activation of adenosine A1 receptors and Gi proteins. During acute myocardial ischemia, sufficient amounts of adenosine for maximal activation of adenosine A1 receptors are released, independent of a preconditioning ischemia. Hence, the protective mechanism of ischemic preconditioning may not exclusively be explained by activation of adenosine A1 receptors. As a working hypothesis, an increased responsiveness of Gi proteins toward receptor-mediated activation, leading to an increased response of Gi-regulated effectors, was tested in this study. In 47 anesthetized dogs, ischemia was induced by proximal ligation of the left anterior descending coronary artery. Animals underwent either a single period of 5 minutes of ischemia (n = 9), a single period of 15 minutes of ischemia (n = 10), 5 minutes of ischemia followed by 15 minutes of reperfusion (n = 8), 15 minutes of ischemia followed by 60 minutes of reperfusion (n = 5), or 5 minutes of ischemia followed by 15 minutes of reperfusion and a second period of 5 minutes of ischemia (n = 15). Sarcolemmal membranes were prepared from the central ischemic area and from the posterior left ventricular wall, which served as the control. During ischemia, carbochol-stimulated GTPase decreased by 38% (control, 33.5 +/- 17.7; ischemia, 24.2 +/- 15 pmol.min-1.mg protein-1; n = 9; P < .001). The decrease in carbachol-stimulated GTPase activity was associated with a 45% decrease in carbachol-mediated inhibition of adenylyl cyclase (control, 28.9 +/- 2.4% maximal inhibition; ischemia, 15.1 +/- 2.6% maximal inhibition; n = 5; P < .001). Prolongation of the ischemic period to 15 minutes did not lead to a further reduction of the Gi-mediated signal transduction. The binding properties of muscarinic receptors were not affected by ischemia. Furthermore, as demonstrated by carbachol-stimulated binding of [gamma-35S]GTP to sarcolemmal membranes, high- and low-affinity binding sites for the muscarinic antagonist carbachol, the EC50 for carbachol-stimulated GTPase activity and the substrate dependency of the high-affinity GTPase, the interaction between muscarinic receptors and inhibitory G proteins, and GTP binding to G proteins were not altered (n = 14). Immunoblotting with alpha 1- and alpha 2-specific antibodies did not indicate a loss of Gi proteins during ischemia that could explain the reduced GTPase activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗