Tension cost correlates with mechanical and biochemical parameters in different myocardial contractility conditions

OBJECTIVES: Tension cost, the ratio of myosin ATPase activity to tension, reflects the economy of tension development in the myocardium. To evaluate the mechanical advantage represented by the tension cost, we studied papillary muscle contractility and the activity of myosin ATPase in the left ventricles in normal and pathophysiological conditions. METHODS: Experimental protocols were performed using rat left ventricles from: (1) streptozotocin-induced diabetic and control Wistar rats; (2) N-nitro-L-arginine methyl ester (L-NAME) hypertensive and untreated Wistar rats; (3) deoxycorticosterone acetate (DOCA) salt-treated, nephrectomized and salt- and DOCA-treated rats; (4) spontaneous hypertensive rats (SHR) and Wistar Kyoto (WKY) rats; (5) rats with myocardial infarction and shamoperated rats. The isometric force, tetanic tension, and the activity of myosin ATPase were measured. RESULTS: The results obtained from infarcted, diabetic, and deoxycorticosterone acetate-salt-treated rats showed reductions in twitch and tetanic tension compared to the control and sham-operated groups. Twitch and tetanic tension increased in the N-nitro-L-arginine methyl ester-treated rats compared with the Wistar rats. Myosin ATPase activity was depressed in the infarcted, diabetic, and deoxycorticosterone acetate salt-treated rats compared with control and sham-operated rats and was increased in N-nitro-L-arginine methyl ester-treated rats. These parameters did not differ between SHR and WKY rats. In the studied conditions (e.g., post-myocardial infarction, deoxycorticosterone acetate salt-induced hypertension, chronic N-nitro-L-arginine methyl ester treatment, and streptozotocin-induced diabetes), a positive correlation between force or plateau tetanic tension and myosin ATPase activity was observed. CONCLUSION: Our results suggest that the myocardium adapts to force generation by increasing or reducing the tension cost to maintain myocardial contractility with a better mechanical advantage.

Lead reduces tension development and the myosin ATPase activity of the rat right ventricular myocardium

Lead (Pb2+) poisoning causes hypertension, but little is known regarding its acute effects on cardiac contractility. To evaluate these effects, force was measured in right ventricular strips that were contracting isometrically in 45 male Wistar rats (250-300 g) before and after the addition of increasing concentrations of lead acetate (3, 7, 10, 30, 70, 100, and 300 µM) to the bath. Changes in rate of stimulation (0.1-1.5 Hz), relative potentiation after pauses of 15, 30, and 60 s, effect of Ca2+ concentration (0.62, 1.25, and 2.5 mM), and the effect of isoproterenol (20 ng/mL) were determined before and after the addition of 100 µM Pb2+. Effects on contractile proteins were evaluated after caffeine treatment using tetanic stimulation (10 Hz) and measuring the activity of the myosin ATPase. Pb2+ produced concentration-dependent force reduction, significant at concentrations greater than 30 µM. The force developed in response to increasing rates of stimulation became smaller at 0.5 and 0.8 Hz. Relative potentiation increased after 100 µM Pb2+ treatment. Extracellular Ca2+ increment and isoproterenol administration increased force development but after 100 µM Pb2+ treatment the force was significantly reduced suggesting an effect of the metal on the sarcolemmal Ca2+ influx. Concentration of 100 µM Pb2+ also reduced the peak and plateau force of tetanic contractions and reduced the activity of the myosin ATPase. Results showed that acute Pb2+ administration, although not affecting the sarcoplasmic reticulum activity, produces a concentration-dependent negative inotropic effect and reduces myosin ATPase activity. Results suggest that acute lead administration reduced myocardial contractility by reducing sarcolemmal calcium influx and the myosin ATPase activity. These results also suggest that lead exposure is hazardous and has toxicological consequences affecting cardiac muscle.

Composition and distribution of muscle fiber types in the rat gastrocnemius muscle / 重庆医科大学学报

Objective:To study the composition and distribution of two muscle fiber types in SD rat gastrocnemius muscle in order to learn its function.Methods:Gastrocnemius muscles of both sides of hind limbs were collected from 10 adult SD rats.8-?m-thick cryostat sections were transected and then stained with the method of myosin-ATPase following a procesure modified partially from one that Guth & Samaha reported before.Results:Gastrocnemius muscle from SD rats can be clearly identified with two different fiber types which are typeⅠ(slow twitch fiber)and typeⅡ(fast twitch fiber) by the myosin-ATPase staining method.Fibers of type I are stained white while fibers of type II are stained brown.The distribution pattern of two types of muscle fibers in gastrocnemius muscles is uniform and chessboard-like.The proportion of typeⅡmuscle fibers contained in the muscle is(72.2?6.8)%,much higher than that of typeⅠfibers which is(27.8?2.4)%(P

Prophylactic Effects of Choline Chloride on Muscle Atrophy in Tail-suspended Rats / 航天医学与医学工程

Objective To study the effects of choline chloride on activities of myosin adenosine triphosphatase (mATPase) of muscle fibres and muscle atrophy in tail-suspended rats. Method Twenty-four adult female Sprague-dawley rats were averagely divided into 3 groups matched for body mass:control group(CON),tail suspension group(TS) and tail suspension group associated with choline chloride(TS+Cch).Weightlessness was simulated by 14 d tail suspension of rats;gastric lavage with choline chloride was given to 1/2 of the rats during tail suspension (15 mg/kg body weight.i.g.).Activities of myosin adenosine triphosphatase (mATpase) of intrafusal and extrafusal fibres in soleus (SOL) muscle were determined by Ca 2+-ATPase method.Paraffin sections of the soleus muscle were prepared by routine histochemistry method. Result After tail suspension for 14 d it was found: 1) percentage of type Ⅱ fibre in SOL of rats treated with choline chloride decreased distinctly as compared with that in the untreated rats (P

Effects of Ischemic Preconditioning on the Left Ventricular Function, Myosin Isozyme, Myofibrillar ATPase Activity and Ultrastructure of the Rabbit Heart

BACKGROUND: Single or multiple episodes of brief period of ischemia and reperfusion(ischemic preconditioning, IP) have been shown to limit infarct size after a subsequent longer period of ischemia. A considerable number of possible mechanisms has been proposed, however, controversies still remain. Accordingly, we evaluated the effect of four cycles of 5 minutes ischemia and 5 minutes reperfusion(IP) followed by subsequent 30 minutes ischemia(ISCH) and 60 minutes reperfusion using isolated Langendorff-Perfused rabbit hearts. Methods and RESULTS: After a 50-minute recovery phase, parameters of the left ventricular function(LVF) including left ventricular developed pressure(LVDP), contractility and the heart rate were recorded, and ultrastructure was examined. Myosin ATPase activity was determined by measurement of inorganic phosphorus and isozymes of the myosin heavy chain were examined by polyacrylamide gel electrophoresis containing pyrophosphate buffer. The ISCH hearts showed severe to irreversible change of the cardiac myocytes homogenously in contrast to the IP hearts in which changes were not homogenous and irreversible injury was only focal. However, parameters of the LVF were not significantly different between the IP and the ISHC hearts during reperfusion. Myosin ATPase activities were also not significantly different(0.67+/-0.123 micromol/mg protein/h in the IP hearts, 0.56+/-0.172 micromol/mg protein/h in the ISCH hearts, and 0.76+/-0.239 micromol/mg protein/h in the control hearts). Band patterns of the myofibrillar proteins, separated by sodium ddodecyl sulfate-polyacrylamide gel electrophoresis, revealed no differences between the IP, ISCH and the control hearts. Myosin heavy chains in the IP and the ISCH hearts were separated into 3 isozymes, V1,V2and V3in pyrophosphate gel electrophoresis in contrast that the control hearts revealed two isozymes, V1and V2. However, there were no differences in the protein composition and electrophoretic motility between the IP and the ISCH hearts. CONCLUSION: These results indicate that IP could not attenuate the changes in LVF, myosin ATPase activity and myosin isozymes on reperfusion, however, it could attenuate the ultrastructural changes of the cardiac myocytes.

Modified procedure for the histochemical demonstration of myosin ATPase / 西安交通大学学报(医学版)

Objective To study the effect of self-modified Guth & Samaha's myosin-ATPase staining method on the classification of SD rat skeletal muscle fiber types.Methods 8 ?m-thick cryostat sections from rat chest muscles and biceps brachii muscles were transfected with cryostat.Myosin-ATPase staining was carried out according to the following procedure: ① Fixing sections for 5 min in fixative solution containing 40 g/L paraformaldehyde;② Rinsing slides in Tris-rinse solution and then preincubating them in alkaline preincubation solution for 15 min;③ Rinsing slides in Tris-rinse solution twice and then incubating them for 60 min in incubation solution;④ Washing slides for three times in 10 g/L CaCl2 and then placing them in 20 g/L CoCl2 for 3 min;⑤ Washing sides in distal water and then placing them in 10 g/L(NH4)2S for 3 min and;⑥ Washing slides in running tap water for 3 min,dehydrating in graded ethanol,clearing in xylene and mounting in neutral balsam.Results After being stained by modified myosin-ATPase staining method,both chest muscle and biceps brachii muscle samples from SD rats could be clearly identified as type Ⅰ fibers and type Ⅱfibers as the fibers of type Ⅰ were stained white while the fibers of type Ⅱ were stained brown.Conclusion Modified myosin-ATPase staining method is a simple and effective way for muscle fiber type classification and can be applied in skeletal muscle related study.

THE CHANGES OF MYOSIN ATPase ACTIVITY AND ITS ISOENZYME DISTRIBUTION IN EARLY STAGE OF CARDIAC HYPERTROPHY FOLLOWING MYOCARDIAL INFARCTION IN RATS / 西安交通大学学报(医学版)

To investigate the changes of cardiac myosin ATPase and its isoenzyme in early stage of cardiac hypertrophy following myocardial infarction(MI), we studied myosin ATPase activitzy, isoenyme distriibution and myocardial fiber diameter of uninfarcted ventricu lar sfptum, 9 aed 21 days after operation in MI rats. The results showed that coincident with the increases in myocardial fiber diameter on 9 days after MI, both myosin ATPase activity and V_1 isoenzyme amount were depressed. These changes were more pronounced on 21 after MI. It is suggested that with the development of myocardial hypertrophy in early stage of MI, adaptive changes in myosin ATPase activity and isoenzyme distribution occur.

STUDY ON COMPARTMENTALIZATION, DIS-TRIBUTION AND CROSS-SECTIONAL AREAS OF FIBER TYPES IN HUMAN DELTOID MUSCLE / 解剖学报

The deltoid muscles on both sides of 8 male cadavers were studied within 24 hours after death. According to its fiber architecture, origins and insertions, and nerve distribution, the deltoid muscle was divided into three compartments: an anterior, a middle and a posterior. The muscle samples were taken respectively from the superficial and the deep portion of each compartment of the deltoid muscle. Frozen transverse sections were stained fer myosin ATPase. Muscle fibers were identified as type Ⅰ and type Ⅱ. The proportion of fiber types in each portion was calculated on microscopic photographs and mean cross-sectional areas of both fiber types were measured by imaging analytical system. The results showed that the proportion of type Ⅰ fiber in the superficial and deep portion of the middle compartment is significantly higher than that of the corresponding portion of the anterior and posterior compartments, and the proportion in the deep portion of each compartment is higher than that of the superficial one, however no difference was found between the left and right sides. The fiber size among all portions is not obviously different, but the diameter of type Ⅱ fiber in the deep portion of the middle compartment is significantly smaller than that of other portions. Except the deep portion of the middle compartment, the diameter of both fiber types of the right muscle is larger than those of the left one, although statistical analysis showed that the difference is not significant. The authors suggest that the difference of fiber type distribution within the deltoid muscle is closely related with the functional differentiation of the muscle and the characteristic higher typeⅠ fiber proportion and smaller type Ⅱ fiber diamiter in the deep portion of the middle compartment probably indicate that the main function of this portion is to keep the shoulder joint stability.