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PubMed1988

Recovery heat production of isolated rabbit papillary muscle at 20 degrees C.

Using metal-film thermopiles, heat production of isolated rabbit papillary muscles was measured under aerobic conditions at 20 degrees C. The time course of total heat production resulting from a single contraction (average of 10) and a twitch train of 10 contractions (0.2 Hz) was separated into initial (I) and recovery heat (R). The time course of recovery heat production of single twitches was characterized by a time constant of 25.4 +/- 1.7 s (mean +/- SE; n = 10). The recovery ratio, R/I, was 1.18 +/- 0.08 (mean +/- SE; n = 7). Total heat produced 25.2 +/- 2.9 mJ.gdw-1 (mean +/- SE; n = 11). After trains of 10 contractions a time constant of 25.2 +/- 1.6 s (mean +/- SE; n = 9) was found. The recovery ratio was 1.14 +/- 0.09 (mean +/-SE; n = 9). Total heat produced was 489 +/- 41 mJ.gdw-1 (mean +/- SE; n = 9). Time constants and recovery ratios for 1 and 10 twitches were not significantly different. This suggests that only the extent but not the nature of the chemical processes after contraction changes when the preparation produces about 20 times more heat. Since the recovery ratio values did not differ largely from the value derived theoretically the conclusion is justified that, under normal aerobic conditions, PCr splitting and its oxidative resynthesis are the major metabolic processes responsible for the energy supply of isolated cardiac muscle.

Animals↗
PubMed1996

[Anomalous insertion of mitral papillary muscles in obstructive hypertrophic myocardiopathy. Report of 2 cases].

Hypertrophic obstructive cardiomyopathy is a pathologic entity whose features are complex and diverse. Its surgical treatment generally requires myectomy. When the left ventricle outflow gradient is also due to mitral valve abnormalities, mitral valve replacement has been considered as the treatment of choice for the relief of the obstruction. We report two cases in which transesophageal echocardiography has allowed a good definition of this complex area of the heart and a better diagnosis and treatment of its components. Its use led to the diagnosis of abnormal papillary muscles inserted directly in the anterior leaflet of the mitral valve, with severe left ventricle outflow obstruction. Surgical treatment consisted of septal myectomy and excision of the muscles, thus preventing the need for mitral replacement. Systolic anterior motion of the mitral valve subsided and the outflow gradients became negligible. This new approach for the treatment of hypertrophic obstructive cardiomyopathy will be of benefit for patients in whom the anomalous insertion of the papillary muscles are recognized before surgery, thus preventing mitral valve replacement.

Adult↗
PubMed1993

Effect of calcium channel agonist (BAY K8644) on volatile anesthetic-mediated depression in neonatal rabbit papillary muscle.

Heart muscle is dependent on the entry of calcium from the extracellular fluid to support contraction, and neonatal hearts are particularly sensitive to reductions in transsarcolemmal entry of calcium. Accordingly, this study evaluated the ability of the calcium channel agonist BAY K8644 to prevent or reverse the myocardial depressant effects of halothane or isoflurane in right ventricular papillary muscles from neonatal rabbits. The ability of BAY K8644 to reverse reductions in force (F) and dF/dt (halothane and isoflurane) or prevent reduction (halothane) was studied. Halothane decreased F to 24 +/- 2% of baseline values (p = 0.001). The addition of BAY K8644 reversed F to only 54 +/- 3% of baseline (p = 0.001 vs. baseline and p = 0.002 vs. halothane alone). Isoflurane decreased F to 20 +/- 2% of baseline (p = 0.001) with a return to 45 +/- 4% of baseline with the addition of BAY K8644 (p = 0.0001 vs. baseline and p = 0.0025 vs. isoflurane alone). With BAY K8644 in the bath prior to the addition of halothane, halothane decreased F to 38 +/- 4% of baseline (p = 0.001). dF/dt mirrored changes in F in all studies. These data show that a calcium channel agonist is only partially effective in modulating volatile anesthetic-induced depression in neonatal rabbit ventricular papillary muscle.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1998

Differential effects of paclitaxel and derivatives on guinea pig isolated heart and papillary muscle.

Paclitaxel (Taxol) is an anticancer agent with clinical activity against various human cancer types. Paclitaxel blocks cell division by stabilizing microtubules, a mechanism that also underlies its major side effects (neutropenia and neurotoxicity). Paclitaxel can also alter cardiac function, and to elucidate the mechanism of this activity, we tested the mechanical and electrical effects of paclitaxel and a series of analogs (docetaxel, taxol B, taxol C and N-methyltaxol C; 5-20 microM) on two different cardiac preparations, the isolated coronary perfused heart and the papillary muscle of the guinea pig. Paclitaxel and N-methyltaxol C induced conduction arrhythmias and reduced coronary flow and left ventricular systolic pressure in the isolated heart, whereas the other taxol derivatives tested had no significant effect. Moreover, paclitaxel blocked the vasodilator effect of bradykinin in the isolated heart. Paclitaxel and N-methyltaxol C produced a positive inotropic effect in papillary muscle, without alterations in the action potential. In the latter preparation, no significant variations were observed after treatment with the other taxol derivatives. The in vitro cardiodepressant and arrhythmogenic activity of paclitaxel is similar to that reported after its clinical administration and might be due to coronary vasoconstriction. The precise role of microtubules as modulators of intracellular calcium in cardiac and smooth muscle cells is at present unclear, because docetaxel and other taxol analogs, though they exhibited similar activity on tubulin, lacked cardiac effects.

Action Potentials↗
PubMed1985

The electromotive force of the ventricular free wall and papillary muscle preparations.

The electromotive force of the ventricular tissues with different anatomy and activation patterns was studied. The left ventricular wall was perfused with Tyrode's solution from the circumflex branch of the left coronary artery and was stimulated first at an epicardial and then endocardial site to induce ectopic beats. The early QRS voltage was compared with the activated area at the same instant. In other experiments, the whole heart was perfused from the aorta, and the anterior papillary muscle of the right ventricle was introduced into a small separate chamber. Different locations were stimulated to induce longitudinal and transverse activation, and the remote potential was measured with leads in both directions. By means of a calibration system with artificial dipoles, the strength of the double layer was expressed in terms of mA X cm per unit area of the activation wave front. The results indicated that epicardial stimulation of the left ventricular wall produced voltage proportional to the activated area; the average moment was found to be 0.11 mA X cm per unit area. The potential curve produced by endocardial stimulation of the same preparation was characterized by an initial low-voltage phase, followed by a sharp upstroke. The right ventricular papillary muscle produced a larger double layer moment during activation in the longitudinal direction, but voltage due to transverse activation was several times smaller.

Animals↗
PubMedDate not supplied

[Arrhythmic activity of the papillary muscle induced by high frequency stimulation: n1 rhythms,transition forms and hysteresis].

Cardiac tissues are able to work within a wide range of frequencies to respond to the changing requirements an organism may have. However, during these frequency variations and under certain pathologic conditions arrhythmias such as blocks, tachycardia, fibrillation, etc, may arise some with fatal consequences. For this reason several experimental procedures have been developed that have shown to be useful in studying whole heart properties, or as an alternative from portions of it when changes in its work rate are imposed. This study reports different phenomena occurring in the papillary muscle of the guinea pig heart when stimulated at very high frequency, of several tens of pps, while analyzing its responses during gradual increments starting at 1 (pulses per second). We found that in our conditions papillary muscles display N:1 rhythms with progressive higher N; further more we found that between one and the next rhythm diverse transition patterns appear, among them a new one that we have named "burst pattern". Finally we show that our system exhibits a generalized process of hysteresis by frequency, being this the first report for guinea pig cardiac tissue and the first one to show also the presence of several hysteresis loops in the same experiment. Due to the large volume of generated data we used a faster and easier way to analyze and display them, based on the fast Fourier transform (FFT). The method is briefly described.

Action Potentials↗
PubMed1999

Posterior myocardial infarction complicated by rupture of the posteromedial papillary muscle.

A 61-year-old man was admitted with acute posterior myocardial infarction and, on physical examination, was shown to have a mitral regurgitation (MR) murmur. Transthoracic echocardiography (TTE) showed severe hypokinesis of the posterior wall and severe MR by color flow. Right heart catheterization with a balloon-tipped catheter revealed a pulmonary artery wedge pressure of 30 mmHg. No 'step-up' was seen in blood samples from the right atrium and right ventricle. On angiography, a subtotal occlusion of the mid circumflex artery was found which was angioplastied and stented. As the patient's clinical condition did not improve, he underwent transesophageal echocardiography (TEE) for further evaluation. This showed complete rupture of the posteromedial papillary muscle. The patient underwent urgent surgery with successful mitral valve replacement. The postoperative course was uncomplicated, and clinical improvement seen. This case report underscores the value of TEE in accurate preoperative diagnosis of papillary muscle rupture by providing preoperative anatomic details of the mitral valve apparatus and surrounding structures.

Cardiac Catheterization↗
PubMed1998

The influence of the neuropeptide galanin on the contractility and the effective refractory period of guinea-pig heart papillary muscle under normoxic and hypoxic conditions.

The aim of this study was to discover the effects of galanin, a neuropeptide comprising 29 amino acids capable of activating inward-rectifier K+ channels (IK1) in cardiomyocytes, on the force of contraction (Fc), velocity of contraction (+dF/dt), velocity of relaxation (-dF/dt) and effective refractory period (ERP) of guinea-pig heart. The influence of galanin on the time-course of hypoxia-induced disturbances in contractility and ERP was also examined. Experiments were performed on the isolated right ventricle papillary muscle of guinea-pig heart. In the concentration range 0.001-0.01 microM, galanin had no significant effect on the measured parameters. At 0.03 and 0.1 microM, galanin exerted a positive inotropic action and prolonged ERP. Further increasing the concentration led to a negative inotropic action and significant shortening of ERP. Although simulated hypoxia induced a significant drop in Fc, +dF/dt and -dF/dt, and a significant shortening of ERP, recovery of all the measured parameters was complete after 10 min reperfusion. In the presence of 0.03 and 0.1 microM galanin the effect of hypoxia on the contractility of papillary muscle was more profound and reperfusion did not result in complete recovery. In contrast, addition of 1 microM galanin to the hypoxic solution significantly protected the muscle and recovery of the tissues during reperfusion was rapid and complete (in 5 min). One can conclude that galanin at lower concentrations induced a positive inotropic action and a prolongation of ERP, but increased the sensitivity of heart muscle to hypoxia. At higher concentrations however, galanin exerted a negative inotropic action but protected the muscle against hypoxia-induced disturbances in contractility.

Animals↗
PubMed1996

Beta-adrenergic responsiveness of papillary muscles in the rat postinfarction model.

Rats in which ligation of the left anterior descending (LAD) coronary artery did not result in an infarct visible to the naked eye have generally been called sham-operated controls and have been used to evaluate changes in the characteristics of the remaining viable myocardium of rats where myocardial infarction was present. Whether these sham-operated rats are equivalent to normal controls or whether they have been altered by the surgery is unknown. The purpose of this study was to evaluate potential differences in papillary muscle mechanical characteristics and responsiveness to beta-adrenergic stimulation in control, open-chest, sham-operated (aborted infarct), and infarct rats 4 weeks after surgery. Absence of significant myocardial damage was verified by morphologic examination in sham-operated hearts: myocardial infarction scar was 1.5 +/- 0.6% (mean +/- SE) of circumference, no infarct being transmural. Basal contractile indices were decreased in papillary muscles in infarct rats compared with the three other groups. The response in contractile indices of infarct muscles to isoproterenol was also less compared with the other three groups. However, although basal contractility was the same in muscles from sham-operated, open-chest, and controls, the responsiveness of sham-operated muscles to isoproterenol was less: change in total tension of 2.9 +/- 1.2% vs. 9.5 +/- 2.7% for controls and 9.3 +/- 2.4% for open-chest (p < 0.05). Percent change in maximum rate of tension development (+dT/dt) was also less in muscles from sham-operated versus control muscles (21 +/- 2 vs. 33 +/- 6%; p < 0.05). Twitch configuration changed similarly with isoproterenol in all four groups. Thus, although contractility is unaffected by sham operation, beta-adrenergic responsiveness of tension-generating indices is modified.

Adrenergic beta-Agonists↗
PubMed1978

Inhibitory effects of vibrations on contractility of isolated rabbit papillary muscle.

The effects of vibrations on myocardial contractility have been tested in isolated rabbit papillary muscles. Sinusoidal longitudinal oscillations were found to inhibit active force in the paced preparation to an extent which depended on vibration amplitude and frequency. The inhibitory effect of vibrations on myocardial contraction resembled that previously seen in other types of muscle. Vibration during the inactive phase did not alter passive muscle tension. When the vibrator was controlled by phonocardiographic recordings from a normal subject or from patients with congenital aortic stenosis, pronounced inhibition was obtained only by vibrations corresponding to a systolic murmur. It is concluded that the myocardium is sensitive to oscillating length changes. If the ventricular muscle in vivo is exposed to vibrations during systole the cardiac function might be seriously interfered with.

Animals↗
PubMed1988

Papillary muscle structure-function relations in the aging spontaneously hypertensive rat.

Isolated left ventricle papillary muscle mechanics and structure were studied in male spontaneously hypertensive (SHR) rats and two control groups of animals, the normotensive Wistar (NR) and the Wistar-Kyoto rat (WKY). Active tension and its first derivative (dT/dtmax) normalized for muscle cross-sectional area were increased in preparations from the SHR at all ages studied relative to control groups (P less than 0.01). However, when these parameters were normalized for myofibrillar cross-sectional area determined from electronmicroscopic point counting data, differences between groups were no longer significant. Force-velocity relations provided no evidence for a depression of shortening velocity at any load in the SHR at any age relative to the two control groups. The duration of mechanical activity, as determined by time-to-peak isometric tension and analysis of muscle force-velocity-time relations, was prolonged only in the 18 month old SHR (P less than 0.01). Thus, while changes in isolated muscle performance occur at a time when hemodynamic impairment is reported in the intact animal (male 18 month SHR), no evidence for depression of isolated muscle function is seen in the SHR at 6, 12 or 18 months of age.

Age Factors↗
PubMed1993

[An emergent surgical case of the traumatic mitral regurgitation due to complete rupture of the papillary muscles].

We present a case of an emergency operation on acute MR and cardiac rupture due to a blunt thoracic trauma. This 27-year-old male suffered a severe blow to the chest when his motorcycle crashed to a tree. He was brought to this hospital by ambulance. On admission, the patient was in shock due to hypotension. Echocardiogram revealed cardiac tamponade and MR of grade 3/4. Pericardial drainage was performed immediately and his condition improved. Systolic pressure of the pulmonary artery was high at 70 mmHg which measured by Swan Ganz catheter. Isolated cardiac injury was diagnosed based on the results of various tests. A sign of acute pulmonary edema progressively deteriolated, therefore, emergent operation was performed on the same day. As cardiac fissure lesions were confirmed under cardiopulmonary bypass, we repaired the inferior side of the left ventricle and then closely examined the mitral valve. Both anterior and posterior papillary muscles were completely torn, so we immediately commenced with procedures to, replace a prosthetic valve. No complication were encountered, and the postoperative course was good. Complete ruptures of the papillary muscles due to trauma is rarely reported. We believe this case is exceptionally uncommon and worthy of reporting.

Accidents, Traffic↗
PubMed1999

Antiarrhythmic effects of magnesium on rat papillary muscle and guinea pig ventricular myocytes.

1. Despite widespread use of magnesium ion (Mg2+) for antiarrhythmic purposes, little direct information is available regarding its antiarrhythmic mechanisms. To elucidate the possible cellular mechanism, the effects of Mg2+ on early afterdepolarization (EAD), delayed afterdepolarization (DAD), triggered activity (TA), transient inward current (TI) and aftercontraction (AC) were examined in various cardiac preparations. The effects of Mg2+ on myoplasmic Ca2+ concentration were also studied. 2. The effects of Mg2+ on AC, induced by overdrive stimulation, were studied in isolated rat ventricular papillary muscle superfused with low K+ solution. In enzymatically isolated guinea pig myocytes, EAD, DAD and/or TA were induced after overdrive stimulation under conditions of superfusion with low K+ solution, using the whole-cell current-clamp method, and TI was also induced by the whole-cell voltage-clamp method. 3. Immediately after changing the solutions, containing varying concentrations of Mg2+, the effects of Mg2+ were examined. In addition, effects of Mg2+ on Ca transient were studied, using fura-2. 4. We found that: (1) in the rat papillary muscle, 10 mM Mg2+ effectively inhibited AC, which was produced after stimulation at both 3.3 Hz and 5 Hz, although 5 mM Mg2+ was without effect in the case of AC induced after 5-Hz stimulation; (2) in the myocytes, 5 mM Mg2+ did not inhibit DADs, EADs and TA, but 10 mM Mg2+ inhibited them completely; (3) the amplitude and frequency of TI decreased significantly in the presence of 10 mM Mg2+; and finally (4) 10 mM Mg2+ inhibited the Ca transient underlying DAD and/or TA. 5. The findings suggest, but do not prove unequivocally, that Mg's actions are probably due to a combination of a shift of the threshold of various ion channels to less negative potentials, a decrease in Ca2+ influx via Ca channels, a block of several K channels, and/or a block of Na-Ca exchanger. In conclusion, the present study indicates that extracellular Mg2+, via whatever mechanism, exerts antiarrhythmic activities.

Animals↗
PubMed1990

Heat released during relaxation equals force-length area in isometric contractions of rabbit papillary muscle.

It has been claimed that the mechanical performance and the related energy turnover of the left ventricle can be reliably predicted on the basis of its time-varying elastance behavior. In its most elementary form, this behavior can be mathematically described by E(t) = P(t)/[V(t)-Vd], where E is ventricular elastance, t is time, P is ventricular pressure, V is ventricular volume, and Vd is the intercept of the end-systolic pressure-volume line on the volume axis. To find out how this behavior of the ventricle as a whole is related to the properties of the myocardium, we tested the energetic prediction for the ventricle that the pressure-volume area of an isovolumic contraction equals the energy released in relaxation in experiments on isolated rabbit papillary muscle at 20 degrees C. To that end, the energy (joules) contained by the force-length area of the muscles, contracting isometrically, was compared with the heat (joules) liberated in relaxation as measured with thermopiles. Mechanical performance of the muscles was varied by altering initial muscle length and external calcium. The slope of the resulting relation between force-length area and heat liberated in relaxation (n = 26) was not significantly different from unity. Thus, the energetic prediction of the time-varying elastance model developed for the whole left ventricle was confirmed by experiments on rabbit papillary muscle at 20 degrees C.

Animals↗
PubMed1997

[Effects of endothelin on electrophysiological and contractile activity of guinea pig papillary muscles].

Effects of endothelin on electrophysiological activity and contractility were examined in guinea pig papillary muscle using intracellular microelectrode and contractile tension recording technique. The results indicated that ET-1 prolonged APD, especially PPD and increased the contractile tension in a dose-dependent manner. The ET-induced effects were not influenced by K+ channel blocker TEA, but inhibited by L-type Ca2+ channel blocker nifedipine, ETA receptor selective antagonist BQ-123 and atriopeptin III in a concentration-dependent manner. It is suggested that the changes in electrophysiological activity and the positive inotropic effect induced by ET-1 in guinea pig muscles are due to the elevation of intracellular calcium, which may be mediated by ETA receptor.

Animals↗
PubMed2005

Insulin-induced changes in beta-adrenergic response: an experimental study in the isolated rat papillary muscle.

BACKGROUND: The aim was to investigate the ability of insulin to modulate the response to beta-adrenergic action on myocardial contractility, assessed as percentage changes of developed tension, in isolated rat papillary muscle. METHODS: Dose-response curves for isoproterenol, calcium, and forskolin were constructed in an incremental fashion with the presence or absence of insulin at the dose of 50 muU/mL. Dose-response curves for isoproterenol on insulin background were also assessed in the presence and absence of a selective antagonist for beta(2)-adrenoceptor, ICI, at the dose of 5 x 10(-8) mol/L. RESULTS: Insulin did not modify the dose-response curve to calcium (EC(50): 1.4 +/- 0.4 mmol/Lfor insulin, n = 8 v 1.5 +/- 0.3 mmol/L for control, n = 8; P = not significant), whereas it was able to shift to the left the dose-response curve and reduce significantly the EC(50) of isoproterenol (EC(50): 0.2 +/- 0.2 nmol/L for insulin, n = 13 v 1.1 +/- 0.4 nmol/L for control, n = 12; P < .01). ICI shifted to the right dose-response curve of isoproterenol and increased about 10-fold the EC(50) value of isoproterenol, but insulin was still able to shift to the left dose-response curve of isoproterenol and to reduce significantly the EC(50) of isoproterenol also in the presence of ICI (EC(50): 11.0 +/- 1.5 nmol/L for ICI, n = 7 v 1.9 +/- 0.8 nmol/L for ICI + insulin, n = 7; P < .01). Insulin did not modify the dose-response curve to forskolin. CONCLUSIONS: Our results suggest that the insulin-induced modulation of contractility is calcium independent and insulin leads to a supersensitization on the beta(1)-adrenoceptors without effects on beta-adrenoceptor independent adenylate cyclase-related pathway.

Adrenergic beta-Agonists↗
PubMed1994

[Anti-hypoxia and anti-glucose deficiency effects of PQS on guinea pig papillary muscle in low frequency electrical stimulation].

Panax quinquefolium saponin (PQS) increases the contractibility of papillary muscle of guinea pigs during electrical stimulation with frequency of 1/8-1/64Hz (P < 0.05). In Krebs-Henseleit solution purged with gas containing 95% N2 and 5% CO2 regardless of containing glucose or not, PQS (0.3mg/kg) has the effect of anti-hypoxia and anti-glucose deficiency (P < 0.05, P < 0.01) in the electrical stimulation with frequency of 1/8-1/64Hz.

Animals↗