Sarcoplasmic reticulum calcium transport and Ca(2+)-ATPase gene expression in thoracic and abdominal aortas of normotensive and spontaneously hypertensive rats

Increased intracellular Ca2+ concentration has been associated with the elevation of vascular tone in hypertensive animals. The increase in free cytosolic Ca2+ may partially result from a reduced activity of the sarcoplasmic reticulum (SR) calcium pump. Accordingly we investigated the Ca2+ transport function and the expression of the Ca(2+)-ATPase gene in thoracic and abdominal aortas of normotensive Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR). Total SR Ca2+ pump activity was estimated by measuring the oxalate-stimulated Ca2+ transport rate on crude homogenates. Ca2+ transport was also measured on highly active microsomal fractions. Our data indicate that the Ca2+ uptake rate, expressed per mg of protein or per g of muscle, is greater in homogenates from aortas of SHR when compared with that of WKY rats. In microsomal fractions isolated from thoracic aortas of SHR compared with WKY rats, the activity and density of SR Ca2+ pump were only slightly increased. The SR Ca2+ transport rate and the amount of each SR Ca(2+)-ATPase mRNA isoform, i.e. SERCA 2a and SERCA 2b, normalized to 18 S ribosomal RNA, were greater in thoracic than in abdominal aorta in both strains. When compared with WKY rats, the level of each SERCA mRNA isoform is higher in the abdominal aorta of SHR but appears similar in the thoracic aorta. Thus, in contrast to previously published data that documented a depressed SR Ca2+ transport activity in the aorta of SHR, the present data indicate that the SR function is increased. These changes in SR activity are accompanied by quantitative changes in expression of the SR Ca(2+)-ATPase gene without alterations in the SR Ca(2+)-ATPase mRNA isoforms pattern.

[Physiopathology of myocardial dysfunction in septic shock]

Left ventricular dysfunction is rarely a prominent feature of septic shock. Initially, it is masked by circulatory changes and adaptive phenomena which increase the cardiac output. Evaluation of intrinsic myocardial function is therefore difficult in this pathology. The different experimental models used (cell culture, isolated muscle, isolated perfused heart and whole animal) and recent clinical studies using angiographic, catheter and echocardiographic data, have confirmed that this condition exists. Its physiopathology is not yet fully understood and involves several mediators. The direct effect of bacterial endotoxins has not been formally established. However, therapy with anti-endotoxin antibodies does give encouraging results. The cytokines, such as interleukin-1, tumour necrosis factor, and platelet activating factor play a key role between the infectious factors and cellular mediators. Their effects on the myocardium are subject of much on-going research. Current date, in particular with respect to the tumour necrosis factor, suggest that they may have a direct cardiodepressor factor. The presence of a circulating negative inotropic substance has been suspected for many years. Recent studies tend to confirm this hypothesis though the substance itself has not yet been isolated. The theory of reduced coronary flow causing myocardial dysfunction in septic shock has fallen out of favour. Some experimental evidence supports the clinical impression of reduced vascular and cardiac reactivity to catecholaminergic stimulation. The actions of different membrane structures involved have not been determined. At cellular level, changes in calcium metabolism, which regulates muscle contraction and relaxation, probably play an important role in septic shock. In addition to the symptomatic therapeutic advances that have been made in septic shock, specific myocardial treatment could be beneficial.

[Protective effects of perindopril in an experimental model of cardiomyopathy]

The effects of an angiotensin converting enzyme (ACE) inhibitor on the intrinsic contractility of the myocardium in cardiac failure have not been studied intensively. The authors studied inotropism, lusitropism and economy of contraction in vitro on left ventricular papillary muscle preparations of cardiomyopathic Syrian hamsters (CSH) treated preventively with perindropil, i.e. before overt signs of cardiac failure. The CSH of the dilated Bio 53.58 strain aged 1 month were treated with perindropil 1 mg/Kg/day for 5 months (PE, N = 11) or with placebo (PL, N = 11) and control hamsters of the F1B strain received placebo (C, N = 7). Compared with C, PL had a significant reduction of the maximal velocity of contraction Vmax (p < 0.01) and of total isometric tension (TF/mm2), p < 0.05, and a reduction of the G curve of the hyperbolic Hill Force-Velocity relationship (p < 0.01). The G value is usually greater in models with improved economy of contraction. When compared with PL, PE showed a 68% inhibition of the plasma activity of ACE, a better Vmax (p < 0.05) but an unchanged TF/mm2. The G value was less depressed than that of C (p < 0.05). The velocity of isotonic relaxation (maxVL) and the negative peak of the derivative of the isometric force (-dF/dt max) were significantly lower in the PL than in the C group but these lusitropic abnormalities remained coordinated with those of the contraction phase, indicating the absence of an intrinsic effect on relaxation in cardiomyopathy. Perindopril prevented the reduction of maxVL but not that of -dF/dt max.(ABSTRACT TRUNCATED AT 250 WORDS)

[Changes in the diastolic left ventricular function in primary antiphospholipid antibody syndrome]

Previous studies have shown that left ventricular (LV) diastolic function is frequently impaired in patients with systemic lupus erythematosus. We prospectively studied echo-Doppler indices of LV diastolic function in 18 patients with primary antiphospholipid syndrome (PAPS), who where compared to a group of 18 healthy controls. Heretofore undescribed LV relaxation abnormalities were found in the PAPS group: this finding suggests the existence of a causal link.

Effects of etomidate on the cardiac papillary muscle of normal hamsters and those with cardiomyopathy

BACKGROUND

Etomidate has been shown to induce no significant inotropic effect on normal myocardium, but its effects on diseased myocardium remain unknown.

METHODS

The effects of etomidate (1 and 5 micrograms/ml) on the intrinsic contractility of left ventricular papillary muscle from normal hamsters and those with cardiomyopathy (strain BIO 82.62, 6 months old) were investigated in vitro (Krebs-Henseleit solution, 29 degrees C, pH 7.40, Ca++ 2.5 mM, stimulation frequency 3/min).

RESULTS

The contractility of papillary muscles from hamsters with cardiomyopathy was less than that of controls, as shown by the decrease in maximum shortening velocity (-25%, P < .001), isometric active force (-45%, P < .01), peak power output (-57%, P < .01), and sarcoplasmic reticulum function (P < .01). Etomidate did not induce a significant inotropic effect, as shown by the absence of changes in maximum shortening velocity and active isometric force, except at 5 micrograms/ml in cardiomyopathic hamsters (+8 +/- 10%, P < .05). The effects of etomidate on these inotropic parameters were not different in normal and cardiomyopathic hamsters. Etomidate impaired contraction-relaxation coupling under low load in both groups, suggesting that etomidate decreased sarcoplasmic function. This impairment was less (P < .02) pronounced in cardiomyopathic muscles. The effects of etomidate on contraction-relaxation coupling under heavy load were not different between groups. In both groups, etomidate had no effect on the peak power output and the curvature of the total force-velocity curve, suggesting that it did not modify the muscle myothermal economy.

CONCLUSIONS

Etomidate had only a slight effect on the intrinsic mechanical properties of hamster cardiac papillary muscles, and these effects did not depend on the pathophysiologic state of the myocardium. These results may be clinically useful as, unlike etomidate, most anesthetics depress myocardial contractility.

Positive inotropic effects of RP 62719, a new pure class III antiarrhythmic agent, on guinea pig myocardium

The mechanical effects of RP 62719 [(-)1-[-2-(3,4-dihydro-2H-1- benzopyran-4-yl)ethyl]-4-(3,4-dimethoxyphenyl)-piperidine] were tested in vitro on guinea pig left ventricular papillary muscle. RP 62719 is a novel pure class III antiarrhythmic agent known to prolong the cardiac action potential duration by selectively blocking the inward rectifying K+ current. Mechanical parameters were determined from contraction and relaxation phases under isotonic and isometric conditions. At a concentration of 0.02 microM, RP 62719 did not produce significant effects on inotropy or lusitropy. At 0.2 and 2 microM, the drug improved contraction under both heavy and low loading conditions, as evidenced by a 30% increase in maximum unloaded shortening velocity (Vmax, P < .001), peak amplitude of shortening (delta L, P < .001), peak isometric active force normalized per cross-sectional area (AF/s, P < .001) and positive peak of the force derivative per mm2 (+dF/s, P < .001). At the same concentrations, positive lusitropic effects were evidenced by an increase in maximum lengthening velocity (maxVr) and negative peak of force derivative per mm2 (-dF/s, P < .001). At a higher concentration (20 microM), effects of RP 62719 on inotropy and lusitropy were less marked, thus accounting for the bell-shaped form of the dose-response curve. An increase in the extracellular Ca++ concentration from 2.5 to 3.75 mM improved inotropy to a similar extent (+30-50%) as did 2 microM RP 62719. However, lusitropy and mechanical coupling between contraction and relaxation were not modified in the same proportion under RP 62719 and under 3.75 mM Ca++.(ABSTRACT TRUNCATED AT 250 WORDS)

[Effects of angiotensin II on intrinsic contractibility of the myocardium in the guinea pig]

Analysis of the contraction-relaxation coupling of guinea pig left ventricular papillary muscle was performed with and without angiotensin II (Ang II 10-6 M). The inotropic and lusitropic properties of Ang II were evaluated at 20 degrees C, 30 beats/min, CaCl2 6H20 2 mM and pH 7.4, under low load (isotonic conditions) and high load (isometric conditions). The maximum velocity of contraction (max Vc) and relaxation (max Vr) were calculated from isotonic contraction having as its only load that corresponding to the imposed preload at Lmax. The maximum positive (+dF/dtmax) and negative values (-dF/dtmax) of the derivative of the force were calculated during isometric contraction. The coefficients, R1 = max Vc/max Vr and R2 = (+dF/dtmax)/(-dF/dtmax), were calculated. These two coefficients allow the contraction-relaxing coupling to be assessed at low and high loads respectively. In the presence of Ang II, the increase in the isotonic velocity of relaxation (1.93 +/- 0.26 vs 3.15 +/- 0.35 Lmax/sec; p < 0.001) was greater than that of the isotonic velocity of contraction (0.74 +/- 0.05 vs 1.02 +/- 0.07 Lmax/sec; p < 0.001). This results in a decrease in the ratio of the velocities of isotonic contraction and relaxation (R1) (0.44 +/- 0.06 vs 0.35 +/- 0.05; p < 0.01). Under isometric conditions, Ang II induced a proportional increase in the parameters of contraction and relaxation. Consequently, there was no significant change in the R2 coefficient (1.22 +/- 0.06 vs 1.12 +/- 0.08). Moreover, Ang II did not induce any change in the sensitivity of the relaxation with respect to load.(ABSTRACT TRUNCATED AT 250 WORDS)

Myocardial contractility, lusitropy and calcium responsiveness in young (50 days) and hypertrophied (180 days) cardiomyopathic hamsters

Contractility, lusitropy and responsiveness to the increase of external Ca2+ concentration were studied in left ventricular papillary muscles of normal and cardiomyopathic Syrian hamsters (SCH) from the UM-X 7.1 strain, both at the onset of myolysis (50-day-old animals) and at the cardiac hypertrophy stage (180-day-old animals) in the absence of congestive heart failure. A marked decrease in all indices of systolic performance was observed in 180-day-old myopathic hamsters as compared to age-matched controls. This was associated with (1) an impairment of the relaxation phase, (2) a loss of the load sensitivity of relaxation, and (3) a decrease in the inotropic and lusitropic responsiveness to Ca2+. On the other hand, when some indices of contraction and the inotropic response to Ca2+ were impaired in 50-day-old myopathic hamsters as compared to age-matched controls, relaxation phase and the lusitropic response to Ca2+ did not alter. This study shows that, in the UM-X 7.1 myopathic hamsters at the earlier stage of the disease, alterations in calcium homeostasis and contraction seem to be the first determinant factors of the development of heart failure when relaxation is not impaired. Conversely, when cardiac hypertrophy has developed, impaired relaxation may worsen heart failure.

Effects of perindopril on myocardial inotropy, lusitropy and economy, and on diaphragmatic contractility in the cardiomyopathic Syrian hamster

Over a 5-month period, 22 1-month-old cardiomyopathic Syrian hamsters were randomly treated with either angiotensin-converting enzyme inhibitor (perindopril 1 mg/kg/day) (PE, n = 11) or placebo (PL, n = 11), and 7 age-matched controls (C) were given placebo. Compared to C, mechanics of left ventricular papillary muscles from PL exhibited a lower maximum unloaded shortening velocity (Vmax) (P less than .01) and normalized peak active force (P less than .05), and a significantly less curved shape of the force-velocity (F-V) relationship (P less than .01). The curvature of the F-V relationship has been proposed as a reflection of the efficiency of muscle contraction. Compared to PL, PE had a 68% inhibition of plasma ACE activity and a greater Vmax (P less than .05), whereas active force (AF) was similar. This resulted in a lesser decrease of the curvature of the F-V relationship compared to that of C (P less than .05). Muscle strips from the ventral costal diaphragm were dissected from the muscle in situ. In both twitch and tetanus modes, intrinsic mechanical performance of diaphragm muscle was markedly decreased in PL compared to C as regards normalized positive (+dF/dtmax/mm2) and negative (-dF/dtmax/mm2) peak rate of force, and normalized peak active force (AF/mm2) (P less than .01 each). In both twitch and tetanus modes, PE had an increased +dF/dtmax/mm2 (P less than .05), -dF/dtmax/mm2 and AF/mm2 (P less than .01 each), compared to PL. These results indicate 1) that the low inotropic state observed in cardiomyopathic Syrian hamsters was associated with decreased myothermal economy of cardiac contraction and with a major impairment of diaphragm intrinsic contractility, and 2) that early therapy with angiotensin-converting enzyme inhibitor helped to preserve myocardial contractility and economy, and diaphragm contractility.

Spontaneous arrhythmias in various models of cardiac hypertrophy and senescence of rats. A Holter monitoring study

OBJECTIVE

The aim was to define experimental models of spontaneous arrhythmias in various models of cardiac hypertrophy in rats.

METHODS

Cardiac hypertrophy was induced by several methods and 24 h Holter monitoring was recorded in conscious rats to quantify spontaneous arrhythmias in hypertrophied hearts. Male Wistar rats were studied. A group of young controls 1-2 months old (n = 16) was compared to four groups of animals with cardiac hypertrophy: (1) thyrotoxic rats which received a daily intraperitoneal injection of L-thyroxine for 7 d (n = 6); (2) rats subjected to abdominal suprarenal aortic stenosis (n = 11); (3) senescent rats 22-24 month old (n = 6); and (4) S-DOCA-salt (senescent animals rendered hypertensive by uninephrectomy and DOCA-salt treatment, n = 8).

RESULTS

(1) Thyroxine resulted in 20% cardiac hypertrophy, with normal arterial tension, sinus tachycardia, a shorter P wave length and PR interval, and frequent (5/6) atrioventricular block. No premature beats were seen. (2) In aortic stenosis, atria and left ventricle were hypertrophied by 53% and systolic carotid pressure increased by 63%. The incidence of supraventricular premature beats was increased [frequency = 0.70 (SEM 0.3) per 24 h in control v 99(61) in aortic stenosis, p < 0.05]. Ventricular premature beats remained as rare as in control. (3) In senescent and S-DOCA-salt rats all types of spontaneous arrhythmias, but specially supraventricular arrhythmias and atrioventricular block, were frequent. Cardiac hypertrophy produced by DOCA-salt treatment in senescent rats had no effect on the incidence and nature of arrhythmias, but resulted in an increased QTc interval.

CONCLUSIONS

Senescent rats and rats with aortic stenosis represent valid models of spontaneous arrhythmias occurring in the absence of ischaemia or toxic insult. Spontaneous arrhythmias in rats are mainly of supraventricular origin. Hyperthyroidism in rats is a model of atrioventricular block probably related to tachycardia. Holter monitoring in rats may have several potential pathophysiological and pharmacological applications.

In vitro effects of propofol on rat myocardium

Propofol is a short-acting intravenous induction agent that induces cardiovascular depression. However, the effects of propofol on intrinsic myocardial contractility remain debatable. Thus, we studied the effects of three concentrations of propofol (1, 3, and 10 micrograms.ml-1, respectively) and its solvent on the mechanics and energetics of isolated rat left ventricular papillary muscles. Propofol and its solvent did not induce any significant inotropic effect as shown by the lack of significant changes in maximum unloaded shortening velocity and in active isometric force. Nevertheless, propofol induced a slight decrease in isometric force (92 +/- 6%, 95 +/- 5%, and 95 +/- 4%, respectively, all P less than 0.01) under certain experimental conditions (i.e., after isometric stabilization). Using various afterloaded twitches, the peak power output and the curvature of the force-velocity curve were calculated. Propofol and its solvent did not significantly modify these two energetic parameters, indicating that it did not change myothermal economy and cross-bridge kinetics. Propofol impaired isotonic relaxation, suggesting that it decreased calcium uptake by the sarcoplasmic reticulum, whereas its solvent alone did not. However, alteration of sarcoplasmic reticulum function was moderate, since postrest potentiation and postrest recovery were unmodified after propofol. It was concluded that propofol induces moderate changes on intrinsic myocardial contractility. These results suggest that cardiovascular depression observed with propofol in vivo is not related to intrinsic myocardial depression.

Elevated blood cyanide concentrations in victims of smoke inhalation

BACKGROUND

The nature of the toxic gases that cause death from smoke inhalation is not known. In addition to carbon monoxide, hydrogen cyanide may be responsible, but its role is uncertain, because blood cyanide concentrations are often measured only long after exposure.

METHODS

We measured cyanide concentrations in blood samples obtained at the scene of residential fires from 109 fire victims before they received any treatment. We compared the results with those in 114 persons with drug intoxication (40 subjects), carbon monoxide intoxication (29 subjects), or trauma (45 subjects). The metabolic effect of smoke inhalation was assessed by measuring plasma lactate at the time of admission to the hospital in 39 patients who did not have severe burns.

RESULTS

The mean (+/-SD) blood cyanide concentrations in the 66 surviving fire victims (21.6 +/- 36.4 mumol per liter, P less than 0.001) and the 43 victims who died (116.4 +/- 89.6 mumol per liter, P less than 0.001) were significantly higher than those in the 114 control subjects (5.0 +/- 5.5 mumol per liter). Among the 43 victims who died, the blood cyanide concentrations were above 40 mumol per liter in 32 (74 percent), and above 100 mumol per liter in 20 of these (46 percent). There was a significant correlation between blood cyanide and carbon monoxide concentrations in the fire victims (P less than 0.001). Plasma lactate concentrations at the time of hospital admission correlated more closely with blood cyanide concentrations than with blood carbon monoxide concentrations. Plasma lactate concentrations above 10 mmol per liter were a sensitive indicator of cyanide intoxication, as defined by the presence of a blood cyanide concentration above 40 mumol per liter.

CONCLUSIONS

Residential fires may cause cyanide poisoning. At the time of a patient's hospital admission, an elevated plasma lactate concentration is a useful indicator of cyanide toxicity in fire victims who do not have severe burns.

[Cardiomyopathy in the Syrian hamster. Physiological and therapeutic aspects]

The primary hereditary cardiomyopathy of the Syrian hamster is a particularly interesting model of experimental cardiomyopathy 1) because of its slow progression to cardiac failure unlike acute experimental volume and pressure overloading; 2) because of the reproducibility and predictable nature of the mechanical, biochemical and electrophysiological abnormalities observed at each stage of the disease; 3) because of involvement of other muscle groups, and particularly, skeletal muscle. The physiopathology is not fully understood but a disturbance of intracellular calcium homeostasis appears to play a major role. From the therapeutic point of view, a number of calcium antagonists have been shown to be effective in restoring myocardial function, but they have no effect on skeletal muscular lesions. Recently, early prophylactic intervention with therapeutic doses of perindopril has been shown to prevent the decrease of certain parameters of myocardial contractility in vitro in the dilated group, before the appearance of any signs of cardiac failure. This study also showed that angiotensin converting enzyme inhibitors had no intrinsic negative inotropic effects.

Effects of hydroxocobalamin on rat cardiac papillary muscle

Hydroxocobalamin is a rapid and powerful antidote in acute cyanide poisoning. The effects of hydroxocobalamin (0.1, 0.3, and 1 mM) on intrinsic myocardial contractility were studied on isolated rat cardiac papillary muscles (n = 10). Whatever the concentration, hydroxocobalamin did not modify the active isometric force and a slight increase in maximum unloaded shortening velocity was noted at 1 mM. Only 0.3 mM significantly impaired contraction-relaxation coupling under low load, suggesting a slight decrease in sarcoplasmic reticulum function. No changes in contraction-relaxation coupling under heavy load were noted, suggesting the lack of modification of myofilament calcium sensitivity. These results suggest that hydroxocobalamin does not induce noticeable changes in intrinsic myocardial contractility. An indirect mechanism might be involved in the previously reported decrease in cardiac function at supratherapeutic concentrations of hydroxocobalamin.

In Vitro Demonstration of the Antidotal Efficacy of Hydroxocobalamin in Cyanide Poisoning

The effects of sodium cyanide (1 mM) and the antidotal action of hydroxocobalamin (1 mM) were studied on rat cardiac papillary muscle. A 10-min period of exposure to cyanide induced a marked decrease in inotropy as shown by a decrease in the maximum unloaded shortening velocity (Vmax: 64 +/- 11% of precyanide values, p <0.01) and active isometric force (AF/s: 35 +/- 13%, p <0.01). The impairment of contraction-relaxation coupling under low load and the nearly complete disappearance of the load sensitivity of relaxation suggested a decrease in sarcoplasmic reticulum function. The proportional acceleration in isometric relaxation suggested a decrease in myofilament calcium sensitivity. There was a nearly complete recovery from cyanide poisoning after 5 min of exposure to hydroxocobalamin, whereas in a control group receiving cyanide alone, the mechanical parameters remained unchanged or were further impaired. The effects of hydroxocobalamin developed very quickly, beat to beat. The main toxic target of cyanide is brain and heart cytochrome oxidase, and brain damage appears only a few minutes after the onset of anoxia. Because hydroxocobalamin is a rapid and powerful antidote, it may be useful in the treatment of acute cyanide poisoning.

[Changes in contraction-relaxation coupling in experimental cardiac hypertrophy in the guinea pig]

Guinea pig myocardium resembles human myocardium with respect to the mechanisms which regulate contractility (enzymatic activity of myosine, functional activity of the sarcoplasmic reticulum). Guinea pig left ventricular hypertrophy (LVH) is therefore a good experimental model for the study of human LVH. The mechanical properties of 5 months old female guinea pigs' left ventricular papillary muscle, 3 weeks after constriction of the abdominal aorta (N = 10), were investigated. Ten papillary muscles of operated control animals and eight of normal guinea pigs submitted to 20 minutes hypoxia were also studied. The animals had no signs of cardiac failure after constriction of the abdominal aorta but the increase in the ratio of heart to body weight (p less than 0.001) confirmed the LVH. When compared with the operated controls, there was a decrease of the maximum velocity of contraction at zero load, of the velocity of contraction with preload alone (Vc), of the total isometric force normalized for the section of the muscle(s) and of the positive peak of the derivative of the isometric force normalized for section (+ dF/s) (p less than 0.001 for each parameter). The parameters of relaxation were also abnormal: decreased velocity of isotonic relaxation with preload only (Vr) and of the negative peak of the derivative of the isometric force normalized for section (- dF/s) (p less than 0.001 for each parameter), and an increase in the half relaxation time (t1/2) (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of ketamine on the cardiac papillary muscle of normal hamsters and those with cardiomyopathy

The effect of ketamine (10(-5) and 10(-4) M) on the intrinsic contractility of left ventricular papillary muscle from normal hamsters and those with cardiomyopathy (BIO 82.62, 6-month old) was investigated. At these concentrations, ketamine induced a positive inotropic effect on normal papillary muscle, as shown by an increase in maximum unloaded shortening velocity (+19 +/- 4 and +34 +/- 5%, P less than 0.05), active isometric force (+32 +/- 8 and +57 +/- 11%, P less than 0.05), and peak power output (+40 +/- 8 and +80 +/- 16%, P less than 0.05), and induced a slight decrease in sarcoplasmic reticulum function. Ketamine had no effect on the curvature of the total force-velocity curve, suggesting that it does not modify myothermal economy. Contractility of papillary muscle from hamsters with cardiomyopathy was less than that of controls, as shown by the decrease in isometric active force (-41%, P less than 0.02), peak power output (-33%, P less than 0.05), and sarcoplasmic reticulum function. The positive inotropic effect of ketamine on papillary muscle from hamsters with cardiomyopathy was less marked than in controls and almost suppressed in some cases: only the maximum unloaded shortening velocity was significantly increased with 10(-5) M ketamine (+7 +/- 6%, P less than 0.05), whereas no significant changes were observed in active isometric force (+14 +/- 8 and +13 +/- 11%; nonsignificant [NS]) and peak power output (+9 +/- 5 and +13 +/- 8%; NS) with ketamine (10(-5) and 10(-4) M, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

The contraction-relaxation coupling during pressure-induced cardiac hypertrophy

Contraction-relaxation coupling was studied in rat and guinea-pig papillary muscles during chronic pressure overload induced by aortic stenosis and during acute hypoxia. Coefficient R1 (ratio between maximum shortening and lengthening velocities of the isotonic twitch loaded with preload only) and coefficient R2 (ratio between the positive and negative peak force derivatives of the isomeric twitch) tested the contraction-relaxation coupling under low and heavy load respectively. Cardiac hypertrophy was similar in guinea-pigs (+43 +/- 5%) and rats (+55 +/- 7%). In both species, cardiac hypertrophy significantly impaired contraction and relaxation phases. In the rat, neither R1 (-1 +/- 4%) nor R2 (-5 +/- 4%) varied significantly during cardiac hypertrophy whereas, in the guinea-pig, an increase in R1 (+56 +/- 18%), P less than 0.001) and in R2 (+26 +/- 9%, P less than 0.01) was noted. These species-related differences might be linked in part to differences in sarcoplasmic reticulum function and myosin ATPase activity. Acute hypoxia, which leads to a decrease in cellular ATP levels, was responsible for a marked decrease in myocardial performance, while R1 increased (+66 +/- 8%, P less than 0.05) and R2 decreased (-14 +/- 1%, P less than 0.05). These results showed that chronic pressure overload modified the contraction-relaxation coupling in a characteristic manner according to the species studied and these changes differed from those observed during acute hypoxia.

Effects of chronic growth hormone hypersecretion on intrinsic contractility, energetics, isomyosin pattern, and myosin adenosine triphosphatase activity of rat left ventricle

We studied papillary muscle mechanics and energetics, myosin phenotype, and ATPase activities in left ventricles from rats bearing a growth hormone (GH)--secreting tumor. 18 wk after tumor induction, animals exhibited a dramatic increase in body weight (+101% vs. controls) but no change in the ventricular weight/body weight ratio. The maximum isometric force of papillary muscles normalized per cross-sectional area rose markedly (+42%, P less than 0.05 vs. controls), whereas the maximum unloaded shortening velocity did not change. This was observed despite a marked isomyosin shift towards V3 (32 +/- 5% vs. 8 +/- 2% in controls, P less than 0.001). Increased curvature of the force-velocity relationship (+64%, P less than 0.05 vs. controls) indicated that the muscles contracted more economically, suggesting the involvement of V3 myosin. Total calcium- and actin-activated myosin ATPase activities assayed on quickly frozen left ventricular sections were similar in tumor-bearing rats and in controls. After alkaline preincubation, these activities only decreased in tumor-bearing rats, demonstrating that V3 enzymatic sites were involved in total ATPase activity. These data demonstrate that chronic GH hypersecretion in the rat leads to a unique pattern of myocardial adaptation which allows the muscle to improve its contractile performance and economy simultaneously, thanks to myosin phenoconversion and an increase in the number of active enzymatic sites.

Inotropic and lusitropic effects of chlorpromazine on rat left ventricular papillary muscle

The in vitro effects of chlorpromazine on rat cardiac papillary muscle were tested at 10(-6), 10(-5) and 10(-4) M. Mechanical parameters were determined from the contraction and relaxation phases under isotonic and isometric conditions in order to assess contraction, relaxation, contraction-relaxation coupling and load sensitivity of relaxation. The peak power output Emax was determined from the force-velocity relationship. At 10(-6) M, a slight positive inotropic effect was observed, probably related to modifications in cross-bridges kinetics. Negative inotropic effects were observed with 10(-5) and 10(-4) M chlorpromazine. At 10(-5) M, shortening of the isometric relaxation and decrease in R2 = (+dF.dt-1max)/(-dF.dt-1max) suggest that chlorpromazine also diminishes myofilament Ca++ sensitivity. Emax was increased at 10(-6) M (19 +/- 5%, P less than .05), but decreased at 10(-5) M (-28 +/- 10%, P less than .05) and 10(-4) M (-82 +/- 2%, P less than .05). Modifications in the force-velocity relationship at 10(-4) M indicated that lowering myocardial performance by chlorpromazine was associated with a low muscle efficiency from a thermoenergetic point of view. At all concentrations, chlorpromazine impaired the isotonic relaxation and load sensitivity of relaxation. At 10(-4) M, muscle contracture and slowed isometric relaxation were probably due to "calcium overload." These results showed that chlorpromazine finely modulates intrinsic cardiac energetics and mechanics by acting on the sarcoplasmic reticulum, myofilament Ca++ sensitivity and cross-bridges kinetics, according to the level of load and chlorpromazine concentration used.

In vitro effects of etomidate on intrinsic myocardial contractility in the rat

Etomidate is available in two different solvents: propylene glycol for induction of anesthesia and ethanol for maintenance of anesthesia. The direct effect of etomidate (1 and 5 micrograms/ml) and of its solvents on cardiac muscle was studied using rat left ventricular papillary muscle. Etomidate induced a slight positive inotropic effect in both solvents, as shown by an increase in maximum unloaded shortening velocity (Vmax) but not in force. At 0.5 mM Ca++ 5 micrograms/ml etomidate increased Vmax (128 +/- 18%, P less than 0.05) but not force (103 +/- 16%, NS). Using various afterloaded twitches, the peak power output (Emax) was calculated: 1 and 5 micrograms/ml etomidate increased Emax (107 +/- 8%, P less than 0.05, and 108 +/- 10%, P less than 0.05, respectively). This increase was related to the increase in Vmax and not in isometric force. Etomidate did not modify the elastic components of papillary muscle, isometric relaxation, and contraction-relaxation coupling under high load. Several findings suggest that etomidate in propylene glycol impaired the sarcoplasmic reticulum (SR) function: 1) it impaired the isotonic relaxation, the contraction-relaxation coupling under low load, and the load sensitivity of relaxation; and 2) it decreased postrest potentiated contraction, which is highly dependent on the SR. Nevertheless, alteration of SR function was only significant at high [Ca++]o and the beat-to-beat postrest recovery was not modified, indicating that the deleterious effects on SR function were moderate. The isotonic relaxation (max Vr) was more impaired by etomidate in propylene glycol (78 +/- 9%, P less than 0.001) and by propylene glycol alone (69 +/- 9%, P less than 0.001) than by etomidate in ethanol (97 +/- 12%, NS) and by ethanol alone (92 +/- 8%, P less than 0.05). This suggests that propylene glycol was responsible for the decrease in SR function. Etomidate in propylene glycol thus has a dual action on rat myocardium: 1) a slight positive inotropic effect due to etomidate per se, and 2) a slight decrease in SR function probably related to propylene glycol. However, because etomidate in propylene glycol induced a slight decrease in isometric force under certain experimental conditions (i.e., after isometric stabilization), etomidate in propylene glycol may induce a slight negative inotropic effect in some clinical conditions as a result of its dual action on the myocardium.

Diazepam does not improve the mechanical performance of rat cardiac papillary muscle exposed to chloroquine in vitro

Diazepam has been reported to decrease the cardiac toxicity of chloroquine but the precise mechanism involved remains unknown. Left ventricular papillary muscles from adult Wistar rats were exposed to 10(-4) M chloroquine and assigned to three groups: group I (n = 10) exposed to chloroquine alone; group II (n = 8) exposed to chloroquine and 10(-5) M diazepam; group III (n = 8) exposed to chloroquine and 10(-4) M diazepam. The main mechanical parameters measured were: maximum unloaded shortening velocity (Vmax), maximum lengthening velocity (maxVr), active force normalized per cross-sectional area (AF/s), contraction-relaxation coupling under low load (R1), load sensitivity of relaxation (Isot.A/Isom.A), and peak power output (Emax) determined from Hill's equation of the force-velocity curve. Data are expressed as mean percent of control values +/- SD, for groups I, II, III respectively. No differences between groups I, II, and III were noted for Vmax (87 +/- 13, 82 +/- 9, 86 +/- 7), maxVr (47 +/- 6, 48 +/- 11, 52 +/- 11), AF/s (87 +/- 16, 91 +/- 10, 83 +/- 11), Isot. A/Isom. A (113 +/- 9, 108 +/- 3, 109 +/- 7), or Emax (75 +/- 10, 81 +/- 12, 72 +/- 16). Chloroquine was shown to be a negative inotropic agent since it decreased Vmax, AF/s and Emax, but diazepam did not restore the intrinsic mechanical performance of rat cardiac papillary muscle exposed to chloroquine, therefore 1) the protective cardiovascular effects of diazepam in chloroquine poisoning are not related to an improvement in intrinsic cardiac mechanical properties; 2) inotropic agents are therefore necessary in combination with diazepam for the treatment of severe chloroquine poisoning.

Inotropic effect of ketamine on rat cardiac papillary muscle

The direct effect of ketamine on cardiac muscle was studied using rat left ventricular papillary muscle. At an extracellular calcium concentration [( Ca++]0) of 2.5 mM, rat myocardial contractility is nearly maximum, and a positive inotropic effect was demonstrated by an increase in maximum shortening velocity (Vmax) with ketamine at 10(-5) M but not 10(-4) M. At a [Ca++]0 of 0.5 mM, ketamine 10(-5) and 10(-4) M had a positive inotropic effect as shown by an increase in Vmax (135% +/- 22% and 147% +/- 33%, respectively) and in isometric active force (AF/s) (120% +/- 10% and 152% +/- 44%, respectively). The positive inotropic effect of ketamine was not related to catecholamine uptake inhibition and/or alpha/beta receptor stimulation because it persisted after phentolamine and propranolol and because ketamine had no relaxing effect. Ketamine 10(-5) and 10(-4) M impaired isotonic relaxation, contraction-relaxation coupling under low loading conditions, and the load sensitivity of relaxation, which suggests impairment of the calcium sequestering systems, especially the sarcoplasmic reticulum (SR). Ketamine modified postrest recovery: the first beat (B1) after a 1-min rest period was decreased by ketamine 10(-4) M but not ketamine 10(-5) M. Moreover, the beat-to-beat postrest recovery has been demonstrated to be exponential, and tau, the time constant of the decay was increased by ketamine 10(-4) M (5.4 +/- 0.3 vs. 3.9 +/- 0.2 beats) but not by ketamine 10(-5) M (3.4 +/- 0.4 vs. 3.7 +/- 0.2 beats). These effects on postrest recovery suggest that ketamine impairs SR function. The authors suggest that ketamine had a dual action on rat myocardium: a positive inotropic effect without any relaxing effect, probably related to an increase in calcium influx, and an impairment of SR function. Nevertheless, impairment of SR is only significant at high concentration (10(-4) M) and might overcome the positive inotropic effect only at supratherapeutic concentration.

Lusitropic effect and modifications of contraction-relaxation coupling induced by alpha-adrenergic stimulation in rat left ventricular papillary muscle

Phenylephrine (PE) and metaraminol (MR) were studied alone at 2 x 10(-5) M and at 4 x 10(-5) M respectively. These drugs were also used both in the presence of either propranolol (PR) at 4 x 10(-7) M (PE/PR and MR/PR groups) or prazosin (PZ) at 2 x 10(-7) M (PE/PZ and MR/PZ groups). Specific alpha-adrenergic stimulation (AS) was induced in the PE/PR and MR/PR groups. These AS were evaluated in isotonic and isometric conditions on rat left ventricular papillary muscle. Peak shortening velocity (Vcmax) and peak lengthening velocity (Vrmax) were calculated from the twitch with preload only. Positive (+dF/dtmax) and negative (-dF/dtmax) peak derivative forces were calculated from the isometric twitch. Two coefficients R1 and R2 were used to measure the coupling between contraction and relaxation at low and heavy load, respectively: R1 = Vcmax/Vrmax and R2 = (+dF/dtmax)/(-dF/dtmax). In all groups, there was a significant positive inotropic effect. As compared to control values before AS, R1 significantly decreased in all groups, (PE/PR: -15%; MR/PR: -18%; PE/PZ: -8%; MR/PZ: -23%; PE: -19%; MR: -32%). On the other hand, R2 significantly decreased only in three groups (PE/PZ: -5.4%; MR/PZ: -16.5%; MR: -12.0%) whereas it did not significantly change in the three other groups (PE/PR; MR/PR; PE). In all groups, and at low load, Vrmax increased more than Vcmax (positive relaxant effect i.e. R1 decreased). At heavy load, despite the positive inotropic effect, there was no significant relaxant effect after predominent alpha-AS. These results indicate that alpha-AS modified the coupling between contraction and relaxation differently, depending on the level of load.

Relaxation of the diaphragm muscle: influence of ryanodine and fatigue

Relaxation of rat diaphragm was shown to be sensitive to load, as previously described for adult mammalian ventricular muscle, because the time course of isotonic relaxation could be changed by changing the load: the lighter the load, the greater the shortening, the quicker the relaxation. Maximum velocity of isotonic relaxation was linearly related to the extent of shortening (r = 0.90). To quantify the degree of load sensitivity, we measured the tRi, i.e., the ratio of time at which the isometric relaxation of the twitch afterloaded at 50% of the isometric peak active tension began to time at which the isometric twitch was relaxed to 50% of the isometric peak active twitch tension. tRi was 0.76 +/- 0.03 (SE) in control conditions but significantly increased to 0.91 +/- 0.02 after ryanodine, which is an inhibitor of the sarcoplasmic reticulum (SR) function, and to 0.89 +/- 0.03 after fatigue. These results suggest that in adult rat diaphragm, as in cardiac muscle, the load sensitivity of relaxation requires a well-functioning SR and that the relaxation abnormalities observed in fatigued diaphragm are related to a dysfunction of the SR.

[Influence of preload on myocardial relaxation in the rat]

Preload, which determines the initial muscle length, has proved to be a basic determinant of the muscle relaxation phase. The mechanical properties of the papillary muscle of Wistar rats (n = 20) were studied at different initial lengths (L): Lmax and 98 p. 100, 94 p. 100, 90 p. 100, 86 p. 100 and 82 p. 100 Lmax. In isometry, the relaxation phase was proportionally less sensitive to a reduction of preload than the contraction phase. When L decreased the peaks of maximal force derivative of the contraction phase (+dF.dt-1 max) and relaxation phase (-dF.dt-1 max) were linearly and significantly lowered at L = 94 p. 100 Lmax and L = 90 p. 100 Lmax respectively. Conversely, in isotonia the relaxation phase was much more sensitive to a reduction of preload than the contraction phase. On a muscle preloaded from 82 p. 100 Lmax to Lmax, the highest max Vr value (i.e. maximal speed of isotonic relaxation) was measured at Lmax, which is the apex of the Starling's isometric curve. When L decreased max Vr decreased linearly and significantly at 94 p. 100 Lmax. In contrast, the maximal speed of contraction (max Vc) increased between Lmax and 94 p. 100 Lmax, became maximal, then significantly decreased beyond 82 p. 100 Lmax. Thus, in the physiological range of the myocardium (Lmax - 85 p. 100 Lmax) the rat papillary muscle tended to maintain its maximal isotonic speed of contraction, or even to increase that speed, whereas the isometric contraction, isometric relaxation and isotonic relaxation phases were early and significantly depressed.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in LV papillary muscle performance and myosin composition with aortic insufficiency in rats

Aortic insufficiency was induced in rats. Left ventricular papillary muscle function was studied after 5, 12, and 40 wk and compared with the papillary muscles from sham-operated animals. The maximum unloaded velocity of shortening, Vmax, was decreased in the rats with aortic insufficiency relative to controls by 15, 20, and 34% at 5, 12, and 40 wk, respectively. The decrease in Vmax occurred concomitantly with a change in the myosin isoenzyme composition such that the V1 isoform content decreased and the V3 isoform increased. Relative to age-matched controls, the V3 content in the hearts with aortic insufficiency had increased by 80, 180, and 125% at 5, 12, and 40 wk, respectively. The decrease in Vmax in the aortic insufficiency group muscles correlated with the change in myosin isozyme composition and could not be explained by changes in collagen content. Thus aortic insufficiency induced changes in myosin isozyme content and Vmax similar to those previously observed with aortic stenosis, thus suggesting a common mechanism of myocardial adaptation to different types of mechanical overload.

Major alterations in relaxation during cardiac hypertrophy induced by aortic stenosis in guinea pig

Left ventricular hypertrophy (LVH) was produced in guinea pigs after aortic stenosis (AS). The percentage of LVH in AS was determined by normalizing left ventricular (LV) weight by the mean LV weight of sham-operated controls (n = 12). After 3 weeks of cardiac overload, a mild LVH (30 +/- 3%) was induced in 17 animals and a relatively severe LVH (56 +/- 3%) was induced in 7 animals. LV papillary muscles were rapidly excised for mechanical studies. No significant differences were observed between control and mild hypertrophy groups. In contrast, a marked decrease in myocardial performance was seen in the more severe cardiac hypertrophy group and was expressed as a percentage of sham-operated levels (Vmax, 22%; active isometric force/mm2, 23%; +dF/dt max/mm2, 26%). Relaxation in this group was still more impaired than contraction (peak lengthening velocity, 14%; -dF/dt max/mm2, 19%). Moreover, the load sensitivity of relaxation was present in both sham-operated controls and mild hypertrophy but almost disappeared in more severe hypertrophy. Isometric relaxation was delayed in the latter group, as shown by the 15% increase of the half-time of the decline of isometric relaxation (t 1/2). On the other hand, acute hypoxia (95% N2-5% CO2 for 20 minutes) also induced a fall in contractility and the disappearance of the load sensitivity of relaxation but with a 67% decrease of t 1/2. Thus, the mechanical analysis of relaxation allows the effects of chronic overload in relatively severe cardiac hypertrophy to be separated from those of acute hypoxia. Moreover, in severe cardiac hypertrophy, the impairment of the load sensitivity of relaxation with increased t 1/2 strongly suggests alterations of the sarcoplasmic reticulum, especially since the moderate decrease in the myofibrillar ATPase activity, which has been observed previously in guinea pig pressure overload, cannot account completely for the marked fall in myocardial performance.

Coordinated changes in contractility, energetics, and isomyosins after aortic stenosis

To investigate possible alterations of myocardial performance in young rats, cardiac hypertrophy was induced by stenosis of the ascending aorta (AS) in three groups of 25-day-old rats that were compared with three groups of sham-operated controls (C). The cardiac overload duration was 8-10 days, 1 mo, and 2 mo in groups 1, 2, and 3, respectively. Mechanics and energetics were studied in left ventricular papillary muscles, and determination of the V1 and V3 isomyosin pattern was achieved in the same papillary muscle. The majority of quantitative changes concerning the cardiac growth process, contractility, and isomyosin shifts occurred within 8-10 days of stenosis. At this point, the degree of left ventricular hypertrophy relative to C was 53 +/- 6%, whereas maximum unloaded shortening velocity (Vmax) decreased significantly (2.8 +/- 0.1 in C vs. 1.9 +/- 0.1 Lmax/s in AS), peak power output (Emax) decreased (1.8 +/- 0.3 in C vs. 0.6 +/- 0.1 in AS), and the curvature of Hill's hyperbola increased (1.3 +/- 0.4 in C vs. 2.0 +/- 0.7 in AS); moreover, the percent V1 isomyosin decreased significantly (98 +/- 1 in C vs. 51 +/- 3% in AS) and the percent V3 isomyosin increased significantly (2 +/- 1 in C vs. 26 +/- 2% in AS). Beyond 8-10 days of AS, additional changes in cardiac hypertrophy and in mechanical and biochemical parameters were less marked.(ABSTRACT TRUNCATED AT 250 WORDS)

[The mechanics of sarcomeres studied using laser diffraction. A study of relaxation]

Myocardial tissues act as an optical filter to light. This is due to their regular striation--periodically alternating clear and dark anisotropic bands. When a narrow band of rat right ventricle is illuminated with a Helium-Neon laser (lambda = 633 nm) diffraction bands are observed, the spacing of which is inversely proportional to the sarcomere length. After muscular stimulation, the displacement of the diffraction bands allows measurement in real time of the contraction and relaxation of the sarcomeres. Sarcomere relaxation comprises two successive experimental phases, one rapid and the other one slow. The time constant of the rapid phase (tau 1) increases linearly with the total load; that of the slow phase (tau 2) decreases. The end of the rapid phase and tau 1 depend on the conditions of load. Our results suggest that the recaptation of calcium by the sarcoplasma reticulum and the affinity of troponine C for calcium depend on the level and changes of load. The affinity of TnC for calcium increases with high load and/or low amplitude of sarcomere shortening: it decreases with low loads and/or high amplitudes of sarcomere shortening.

Relationship between inotropy and relaxation in rat myocardium

Myocardial mechanics of 56 rat papillary muscles were investigated in various inotropic states, i.e., early postpartum (1st day, 1st mo) and, in adult, by altering external calcium concentration, [Ca2+]0, stimulation frequency (F), and initial muscle length (L). In all these protocols, the decrease of the inotropic level paralleled a progressive diminution in load sensitivity of relaxation. In such protocols modifying cardiac contractility, peak shortening velocity of the twitch with preload only at Lmax (Vcmax) was always less depressed than peak lengthening velocity (Vrmax), and the ratio R1 = Vcmax/Vrmax always increased. This increase of R1 was linearly related with the decrease of the maximum unloaded shortening velocity (Vmax). The ratio R2 (positive over negative peak force derivatives of the isometric twich at Lmax) was significantly lowered in newborn and was lowered in adult for [Ca2+]0 less than or equal to 1 mM and L less than or equal to 94% Lmax. For a given change in Vmax, each of the experimental protocols gave rise to specific changes in contraction-relaxation coupling tested at low load (R1) and at heavy load (R2).

[In vitro opening of human atheromatous coronary arteries using a pulsed laser]

This study was undertaken to assess the respective values of pulsed and continuous laser emission for in vitro recanalisation of very stenosed atheromatous human coronary arteries. The Nd-YAG laser used emitted a 10 Hz 10 ns burst in the infrared band (1 064 microns). Previous spectroscopic studies had shown no specific band of absorption in the spectral field of emission of the usual lasers. The laser beam was focused in the axis of the segment of coronary artery irradiated. The crater or neo lumen obtained usually had irregular walls. No perforation of the arterial wall or macroscopic debris were observed. Histological studies showed minimal burn lesions with sparse coagulation necrosis limited to a few tens of micron thickness. The percentage recanalisation obtained with pulses of 200 mJ attained 50% for a total energy of 450 J delivered in 2 mn. This study confirmed the feasibility of disobliteration of atheromatous coronary arteries by pulsed laser. Our results suggest that ultra short pulsed laser acts more by a mechanical than by a thermal mechanism which may lead to less side effects than observed in vivo with continuous laser emission.

Real-time kinetics of sarcomere relaxation by laser diffraction

Kinetics of sarcomere movement were studied in real-time by laser diffraction. Instantaneous sarcomere shortening was measured during afterloaded twitches simultaneously with instantaneous shortening and tension of the whole trabecula excised from rat right ventricle. Resting sarcomere length at optimal length was 2.20 +/- 0.02 micron (mean +/- SEM). Maximum amplitude of sarcomere shortening was 0.30 +/- 0.01 and 0.16 +/- 0.01 micron, respectively, in twitches loaded with preload only, and in "isometric" twitches. When the isotonic load (expressed as a percentage of maximum isometric force TF) increased, the maximum velocity of sarcomere relaxation max Vr (micron/sec) decreased: max Vr = -4 exp (-2.5 X 10(-2) % TF); r = 0.95. The time course of sarcomere relaxation appeared to be progressively delayed when the total load increased from preload only up to "isometric" load. Sarcomere relaxation occurred in two successive exponential phases, a rapid phase [time constant (msec): tau 1] followed by a slower one (time constant: tau 2). When the total load increased, tau 1 increased and tau 2 decreased according to the linear relations: % TF = 0.2 tau 1 + 4.8 (r = 0.83) and % TF = -0.1 tau 2 + 157 (r = 0.95). The relative predominance of both the time course and the amplitude of these two phases depended upon the level of total load. The rapid process predominated at low load, the slow one at high load. The role of load and/or shortening in the time course of these two phases is discussed.

Left ventricular isomyosins in normal and hypertrophied rat and human hearts

Regulation of rat cardiac contractility by changes in the expression of a particular form of myosin (V1-V3) has been demonstrated with a pressure overload. Previous reports of the effect of a volume overload have been controversial. Therefore, we measured the isomyosin composition and mechanical function in the same papillary muscles from rat hearts subjected to a chronic volume overload (aortic insufficiency, AI). A marked change in isomyosin composition from V1 to V3 occurred. Contractility, as assessed by shortening velocity Vmax, was also significantly decreased, and this decrease was correlated with the isomyosin transformation. The changes in isomyosin composition and speed of contraction with AI are thus similar to changes induced by aortic stenosis. Little experimental evidence exists for involvement of such changes in the regulation of human cardiac contractility. Using immunoglobulins highly specific for V1 and V3 in autopsy samples we have observed that the human left ventricle is mostly composed of a V3 isoform (HV3) and that small amounts (1 to 15%) of a V1 type (HV1) are present in foetal and some adult hearts. This HV1 is absent from the left ventricles of patients with valvular disease, assessed at the time of valve replacement (N = 30, samples provided by Dr P. Menasché). Myosin Ca2+-stimulated ATPase activities were not significantly different between normal and hypertrophied hearts. These data demonstrate the heterogeneity of human ventricular myosin, which is composed of V1 and V3 isomyosins, as in other mammalian species. Isomyosin shifts from V1 to V3 are possible in man, but they are quantitatively small and without noticeable influence on overall ATPase activities.

Relaxation of mammalian heart muscle during chronic cardiac overload

Cardiac relaxation was studied in rat papillary muscle during hypertrophy induced by different chronic volume and/or pressure overload (aortic insufficiency, aorto-caval fistula, aortic stenosis, spontaneously hypertensive rat). Maximum velocity of lengthening did not depend upon the degree of cardiac hypertrophy, but rather on the type of chronic overload. Cardiac hypertrophy did not modify the load sensitivity of relaxation, whatever the type and stage of chronic overload, although, during acute hypoxia, the load sensitivity disappeared both in normal and in hypertrophied heart muscle.

Load sensitivity of relaxation in the foetal and newborn rabbit heart

Differences in the mechanism of cardiac relaxation and the influence of changes in the stimulation frequency were studied in foetal and newborn rabbit hearts. In the foetal rabbit heart which lacks a well developed sarcoplasmic reticulum, load sensitivity of relaxation was investigated and compared with that observed in the newborn. Load sensitivity was studied by measuring force and shortening length in twitches with increasing afterloads and also when load clamp steps were rapidly imposed during the twitch. Quantification of the load sensitivity was achieved by the measurement of the time to relaxation "tRi" which was linearly related to the relative developed force. The slope (S) of this linear relation quantifies the load sensitivity: the higher the slope, the more load sensitive is the relaxation. At a frequency of 24 beats X min-1, S was respectively 0.24 in the foetal heart and 0.36 in the newborn heart showing at both ages the existence of a load sensitivity and its significant increase at birth. No further increase in load sensitivity was observed from 1 day to 21 days after birth. Reducing the stimulation frequency from 24 to 10 beats X min-1 abolished the load sensitivity in foetal hearts (S = 0.05) while, in the newborn, a significant load sensitivity could still be observed (S = 0.25). Thus, in rabbit myocardium, the load sensitivity of cardiac relaxation depended upon the age and the stimulation frequency showing a perinatal development of the structures involved in the control of myocardial relaxation.

[Cardiac relaxation in experimental chronic myocardial hypertrophy: role of the sarcoplasmic reticulum]

The relaxation phase was studied in normal rat hearts submitted to chronic myocardial pressure and/or volume overload (stenosis of the abdominal aorta, aortic regurgitation, aorto-caval fistula) and in spontaneously hypertensive rats, some of which also had aorto-caval fistulae. Four indices were chosen to quantify the relaxation phase: maximal velocity of relaxation during contraction with preload alone, the negative peak of the derivative of isometric tension, and two other indices testing the sensitivity of the relaxation phase to other conditions of load. The first two indices were found to be depressed during chronic myocardial overload, especially with aorto-caval fistulae and mixed overload. On the other hand, the other two indices of the degree of sensitivity to the relaxation load by two different methods showed no significant difference between chronically overloaded and control hearts, though changes were observed after acute hypoxia. These two indices are related to morphological development and to the functional state of the sarcoplasmic reticulum. These results suggest that the rate of calcium uptake by the sarcoplasmic reticulum is reduced during chronic myocardial overload but that the myocardium retains its ability to regulate the relaxation phase with respect to time and the degree of total load. This property disappears temporarily after hypoxia when the heart behaves like frog myocardium which has practically no sarcoplasmic reticulum.

[The use of lasers in the study of cardiac mechanics]

Cardiac and skeletal muscles exhibit regularly spaced light and dark transverse striations (the I and A bands respectively). Consequently, when they are illuminated by a laser beam, they behave like diffraction gratings. The diffraction line spacing varies inversely with the sarcomere length. Real-time kinetics of sarcomere can be measured with a high accuracy. The analysis of the diffraction pattern indicates a high degree of synchronization of sarcomere movements (contraction and relaxation). This technique represents a powerful method to analyse the mechanical behaviour of heart muscle at subcellular level.

Spectral evidence for sub-picosecond iron displacement after ligand detachment from hemoproteins by femtosecond light pulses

We have measured spectral and kinetic differences in protoheme, sperm whale or horse heart myoglobin and human hemoglobin following photodissociation induced by optical pulses of 80 fs duration. Full ligation was performed with oxygen or carbon monoxide. Femtosecond kinetics and transient difference spectra revealed the appearance of a deoxy species with tau approximately equal to 250-300 fs. The transient deoxy species in myoglobin and hemoglobin evidenced a 3-4 nm red shift of their delta A spectra compared with the equilibrium delta A spectrum. This shift was not observed after photodissociation of the carbon monoxide liganded protoheme. We proposed that the 250 fs time constant corresponding to the appearance of the deoxy-like species is related to the displacement of the ferrous iron out of the heme plane. Consequently, the small red shift of the delta A spectra observed in photodissociated hemoproteins may be tentatively attributed to changes in the vibrational modes of either the proximal histidine-Fe2+ bond and/or of the N4 porph-Fe-N epsilon His (F8) bent.

Force-velocity-length relationship during cardiac hypertrophy. Time course of activation

Basic mechanical properties observed during cardiac hypertrophy were studied in left ventricular rat papillary muscles after exposure to chronic pressure and/or volume overloading. It is always possible, during such overloading conditions, to define the level of contractility in terms of a force-velocity-length (F-V-L) relationship regardless of time and initial length. Thus, during a determined period of the contraction phase and for a given total load, shortening velocity remained an univocal time-invariant function of shortening length, involving a time-independent maximum intensity of activation. The onset of this precise phase was reached relatively soon after stimulus. The time-independent F-V-L relation was observed both in controls and in hypertrophied heart muscles, whatever the degree and the type of induced hypertrophy, and even during the latest phases of congestive heart failure.

Femtosecond photolysis of CO-ligated protoheme and hemoproteins: appearance of deoxy species with a 350-fsec time constant

Photolysis of HbCO, MbCO, and CO-protoheme has been investigated by measuring transient differential spectra and kinetics of induced absorption after excitation with a 250-fsec laser pulse at 307 nm. Probing was performed by a part of a continuum pulse between 395 and 445 nm. Photodissociation of the three liganded species occurred within the pulse duration. By contrast, the formation of deoxy species appeared with a mean (+/- SD) response time of 350 +/- 50 fsec. This time constant was identical for the three species and independent of the presence or absence of the protein structure. Our results suggest the formation of a transient high-spin in plane iron (II) species which relaxes in 350 fsec to a high-spin stable state with concerted kinetics of CO departure and iron displacement. The spin transition is suspected to occur via liganded excited states which relax in part to non-reactive states with a 3.2-psec time constant.