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At least 613 records · Page 34Linked to original sources
PubMed1998

Effects of metallothionein on action potentials of anoxic and reoxygenated papillary muscles of guinea pigs.

AIM: To study anti-arrhythmic effects of metallothionein (MT). METHODS: Standard microelectrode technique was used to study the effects of MT on action potentials (AP) in anoxic and reoxygenated papillary muscles of guinea pigs. RESULTS: MT (0.02 mmol.L-1) had no effects on AP of the normal papillary muscles; when the muscles were exposed to ischemic solution without MT, there was a marked shortening of action potential duration (APD) at 20%, 50%, and 90% of repolarization (APD20, APD50, APD90) from 82 +/- 7 to 37 +/- 7, 131 +/- 35 to 63 +/- 11, and 167 +/- 12 to 100 +/- 19 ms, respectively, (P < 0.01); and an obvious reduction of resting potential (RP), action potential amplitude (APA), and the maximal upstroke velocity of phase 0 (Vmax) from -92 +/- 9 to -63 +/- 12 mV, 135 +/- 13 to 80 +/- 8 mV, and 286 +/- 55 to 164 +/- 42 V.s-1, respectively (P < 0.01). However, in the presence of MT, the AP parameters (RP, APA, and Vmax) changed from -63 +/- 2 to -82 +/- 1 mV, 80 +/- 8 to 104 +/- 25 mV, and 164 +/- 42 to 237 +/- 43 V.s-1, respectively, (P < 0.01), except that APD20, APD50, and APD90 shortened further from 37 +/- 7 to 12 +/- 3, 63 +/- 11 to 28 +/- 7, and 100 +/- 19 to 82 +/- 11 mV, respectively (P < 0.01). MT decreased the incidence of automaticity during reoxygenation from 91% to 33%. CONCLUSION: MT possesses a calcium regulatory property.

Action Potentials↗
PubMed1989

[Influence of adaptation to stressor effects on bioelectrical activity, contractile function and resistance of the papillary muscles to the excess of intracellular calcium].

In experiments on papillary muscles of rats it was established that adaptation to stressor effects increases resistance of the myocardium to contracture effects and restricts depression of electrophysiological parameters caused by the excess of calcium. Such adaptation decreased contracture by 6.5 times. On the next stage it was established that adaptation restricts depression of electrophysiological parameters of cardiomyocytes with the action of large concentrations of calcium. Possible mechanism of cardiac protector effect of adaptation to stressor effects is being discussed.

Adaptation, Physiological↗
PubMed1991

Alpha 1-adrenergic stimulation increases the Vmax of isolated myocardial papillary muscles.

alpha-Adrenergic agonists have been shown to increase the tension developed by myocardial muscle. However, their effects on the maximum velocity of unloaded muscle shortening (Vmax) have not been rigorously examined. In this study, the contractile effects of the alpha-adrenergic agonist phenylephrine were examined in the presence of propranolol in papillary muscles of two species, the dog and the rabbit. In rabbit papillary muscles studied at physiological calcium concentrations (1.25 mM), phenylephrine increased all indices of contractility (Vmax, tension, and maximum rate of tension developed (dT/dt)) starting at 10(-8) M. The percent increase in Vmax (121 +/- 8%) was less than that of tension (188 +/- 20%, p less than 0.05) and dT/dt (262 +/- 35%, p less than 0.01). These findings occurred at both 29 and 35 degrees C and were inhibited by adding 10(-5) M prazosin. Increasing extracellular calcium concentration from 1.25 to 15 mM caused changes in twitch configuration that were significantly different from those of phenylephrine. Calcium increased all indices of contractility more than did phenylephrine. This was particularly true for dT/dt (502 +/- 82 vs. 262 +/- 35% for phenylephrine, p less than 0.01). Nonetheless, the ratio of increase in tension to increase in Vmax under both experimental conditions was similar (the increase in Vmax was 64% of that of tension with phenylephrine and 69% with increased calcium). At 1.25 mM calcium, the increase in contractility caused by phenylephrine was much smaller in dog myocardium as compared with rabbit myocardium. Rather, the effects of phenylephrine on dog myocardium studied at 1.25 mM calcium resembled that of rabbit myocardium studied at 15 mM calcium.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2001

Ruptured papillary muscle after mitral valve replacement with preservation of chordae tendineae.

Many cardiac surgeons believe strongly that every effort should be made to preserve the continuity of the mitral anulus, chordae tendineae, and papillary muscles during mitral valve replacement in order to maximize ventricular function and maintain normal ventricular geometry. We treated a patient with spontaneous papillary muscle rupture after mitral valve replacement in whom efforts had been made to preserve continuity of the mitral mechanism.

Adult↗
PubMed1985

The rate of resting heat production of rat papillary muscle.

The rate of resting heat production of quiescent rat left ventricular papillary muscles was measured myothermically. The effects of contractile activity, stretch, oxygen partial pressure, temperature, amino acids and time were examined. The rate of basal heat production was the same throughout the day whether or not muscles contracted isotonically under a small pre-load. Passive stretch increased the rate of resting heat production; the stretch-induced increment was highly variable from muscle to muscle. The resting heat rate per se was only moderately sensitive to oxygen partial pressure and temperature, and was insensitive to the presence of amino acids in the bathing medium. The stretch-induced increase in resting heat rate was independent of these three factors. The rate of resting heat production declined exponentially with time to reach a plateau about 4 h following cardiectomy.

Amino Acids↗
PubMed1977

Postnatal maturation of noradrenaline uptake and release in cat papillary muscles.

Catecholamine uptake and release have been studied in isolated right ventricular papillary muscles from kittens aged less than 24 hours, 16 to 18 days and 28 to 32 days. Under the age of 24 h catecholamine uptake (uptake I) does not appear to be functioning and at this age there is a significantly lower response to tyramine. These results suggest that myocardial sympathetic innervation continues to mature, in the cat, after birth.

Animals↗
PubMed1977

Sarcolemmal sodium permeability and contractile force of guinea pig papillary muscle: effects of germitrine.

The action potential of guinea pig papillary muscle exposed to the ceveratrum alkaloid germitrine (2 mugM) is followed by a long-lasting after-depolarization (maximal amplitude, 8 mV; half-time of decay, 32 seconds; total duration, approximately 75 seconds). This after-depolarization interrupts the terminal phase of repolarization. During repetitive stimulation (0.1-1.0 Hz; 80 nM germitrine) the after-depolarizations that follow consecutive action potentials are summed, causing persistent depolarization of up to 10 mV. The after-depolarization is reversibly abolished by tetrodotoxin (TTX). Test contractions evoked at various times during or after the germitrine-induced after-depolarization reveal a phase during which the ability of the muscle to develop force is transiently increased. This positive inotropic influence reaches its maximum 1 minute after the conditioning stimulus and thereafter decays with a half-time 4.8 times longer than the half-time of decay of the after depolarization. It is reversibly abolished by TTX and augmented by dihydro-ouabain (DHO). We conclude: Germitrine induces an after-depolarization by prolonging dramatically the Na permeability component which is mediated by the fast Na channels and normally restricted to the first few milliseconds of the action potential. The germitrine-induced selective and persistent increase of sarcolemmal sodium permeability (PNA) causes a positive inotropic effect, probably because intracellularly accumulating Na ions exchange for extracellular Ca ions.

Action Potentials↗
PubMed1996

Electrical heterogeneity and conduction block in reoxygenated guinea pig papillary muscles.

To investigate the changes in electrical activity after reoxygenation, guinea pig papillary muscles were reoxygenated with 5 mM glucose solution after various durations (30-120 min) of substrate-free hypoxia. Action potential duration recovered to the control level on reoxygenation following 30-120 min hypoxia. The recovery of developed tension or resting tension was incomplete after reoxygenation following longer periods of hypoxia. There was a high incidence of arrhythmias on reoxygenation after 60 min hypoxia, which have been shown to be triggered activities due to delayed afterdepolarizations. In some muscles reoxygenated after prolonged hypoxia (90-120 min), there was electrical heterogeneity which was shown by variable action potential durations and configurations. There was also conduction block around the microelectrode site in muscle. It was suggested that the electrical heterogeneity and conduction block could predispose to reentry, and that triggered activities and reentry could be involved in the genesis of arrhythmias on reperfusion.

Action Potentials↗
PubMed1989

The effect of noradrenaline on the ability of rat papillary muscle to resist an acute respiratory acidosis.

We have studied the effect of an increase in extracellular calcium and of noradrenaline on the ability of rat right ventricular papillary muscle in vitro to resist an acute fall in extracellular pH (pHe) produced by a rise in superfusate PCO2. We found a steep linear relationship, slope 0.86(SEM 0.06), r = 0.94, between a plot of logarithmic change in tension against pHe for control muscles (superfusate containing 1.8 mmol.litre-1 calcium). An increase in extracellular calcium (3.6 mmol.litre-1) increased absolute tension but did not alter the slope significantly. Increasing concentrations of noradrenaline (6.3 x 10(-8) to 6.3 x 10(-6) M) progressively reduced the slope of the tension/pHe plot from 0.82(0.05) to 0.35(0.07), p less than 0.001. Noradrenaline improved the ability of rat papillary muscle to resist an acute acidosis by a mechanism independent of changes in calcium concentration.

Acidosis, Respiratory↗
PubMed1989

[The action of ultrasound on the contraction strength and action potential of the papillary muscle of the rat heart].

In experiments on isolated rat papillary muscles the effects of therapeutic doses of ultrasound (US) (intensity, less than 2 W/cm2) with frequency of 0.88 MHz on contraction force and action potential (AP) were studied. 12 muscles (from 14) responded to 3-min exposition of the US with a rise both in contraction force and in resting tension. Sensitivity to US and a value of inotropic effect changed significantly between the preparation, and the threshold intensities of US varied from 0.3 to 2 W/cm2. In 3 experiments the inotropic effect of US was more than 100%, but in others it was about 50%. Two preparations were not sensitive to the US. The positive inotropic effect of US was accompanied by membrane depolarization (up to 20 mV) and by prolongation of AP duration measured at 10% of its amplitude (APD10). The correlation between the increase in contraction force and APD10 was demonstrated. Some preparations responded to US with high depolarization (up to 50 mV) and were inexcitable. The US induced an increase in temperature less than 1 degree C, therefore all the effects of US could not be explained as a result of temperature rise.

Action Potentials↗
PubMed1981

Effects of hypoxia and metabolic inhibitors on the electrical and mechanical activities of isolated guinea pig papillary muscles.

Electrical and mechanical activities of the isolated guinea pig papillary muscle were measured simultaneously, and the effects of various degrees of hypoxia and metabolic inhibitors were examined. Hypoxia selectively diminished the action potential duration (APD) dependently upon the degree of hypoxia with little affecting the other parameters of the action potential. Hypoxia concomitantly depressed the contractile force (CF), but the decrease in CF always preceded the decrease in APD; thus, the complete excitation-contraction uncoupling was sometimes observed. Metabolic inhibitors (dinitrophenol, DNP and monoiodoacetic acid, IAA) produced qualitatively the same changes in the electrical and mechanical activities. However, DNP mimicked hypoxia better than IAA which produced rather parallel decreases in CF and APD. The slow response action potential (elicited after inactivation of the excitatory fast Na system of the membrane) was completely blocked by hypoxia and metabolic inhibitors, which was partially restored by isoproterenol, histamine and tetraethylammonium. When isoproterenol was present in the bathing solution, the decreases in CF and APD produced by hypoxia were accelerated, but ATP and propranolol did not significantly modify the hypoxically induced changes.

2,4-Dinitrophenol↗
PubMed1985

Contribution of activation-inactivation dynamics to the impairment of relaxation in hypoxic cat papillary muscle.

Previous investigation of conventional isometric twitches of normothermic cat papillary muscle has shown that hypoxia prolongs relaxation, and this prolongation is actually accentuated during early reoxygenation. Our aim was to identify how hypoxia and reoxygenation affect the coupled processes of activation and inactivation that govern the time course of internally generated contractile tension (Ti). Activation and inactivation are modeled as first-order processes with rate constants ka and ki, respectively, and the overall isometric muscle as an underdamped second-order lag system driven by Ti. The analytical expression (To) for the externally recorded tension is dominated by two exponential terms incorporating ka and ki. Accurate least-squares fits of digitized twitches to To yielded estimates of ka and ki at 1- to 3-min intervals during control oxygenation, hypoxia, and early and late reoxygenation. Results follow. Compared with control, normothermic hypoxia prolonged activation [at 15 min ka decreased 61% from control, 35.5 +/- 6 (SE) s-1, P less than 0.05] and accelerated inactivation (at 15 min, ki increased 69% from control, 6.0 +/- 0.5 s-1, P less than 0.05). In early reoxygenation (1-3 min) activation remained impaired and inactivation returned to control levels (ki decreased 16% from control, NS). In late reoxygenation (15 min) both processes reverted to control. Thus inactivation kinetics can be dissociated from activation kinetics. Impaired relaxation in normothermic hypoxia is due to prolonged activation, whereas inactivation is actually accelerated. The further impairment of relaxation in early reoxygenation is due to rapid return of inactivation to control at a time when activation is still prolonged.

Animals↗
PubMed1990

Effects of inhibitors of protein kinase C and Na+/H+ exchange on alpha 1-adrenoceptor-mediated inotropic responses in the rat left ventricular papillary muscle.

1. Alpha 1-adrenoceptor stimulation of rat left ventricular papillary muscle produced a triphasic inotropic response: an initial transient positive inotropic effect (PIE) followed by a transient negative inotropic effect (NIE) and a sustained PIE. 2. The protein kinase C inhibitor, staurosporine, at concentrations ranging from 30 nM to 100 nM inhibited the sustained PIE, but had no significant effect on the transient PIE and NIE. 3. H-7, 1-(5-isoquinoline sulphonyl)-2-methylpiperazine, a less specific inhibitor of protein kinase C than staurosporine, at a concentration of 100 microM inhibited both the transient NIE and the sustained PIE without affecting the transient PIE. 4. Amiloride, an inhibitor of Na+/H+ exchange, at concentrations ranging from 0.1 mM to 1 mM inhibited the sustained PIE and, at higher concentrations, also inhibited the transient NIE. 5. An amiloride analogue, 5-(N-methyl-N-isobutyl)amiloride (MIBA), inhibited only the sustained PIE with an IC50 of 0.3 microM which is approximately two orders of magnitude lower than amiloride. 6. The receptor-linked stimulation of Na+/H+ exchange through protein kinase C activation may be a mechanism for alpha 1-adrenoceptor-mediated sustained PIE.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1982

Mechanism of plateau loss in rabbit papillary muscle after a short rest. Role of outward current.

Shortening of the first action potential plateau phase and potentiation of isometric contraction are simultaneously found in rabbit papillary muscle after 1 min of rest. The ionic nature of these events was investigated. Shortening of the plateau phase is not markedly prevented by activators of the slow inward current (5'-guanyl imidodiphosphate, 10(-5) M plus isoproterenol, 10(-7) M) but is completely eliminated by potassium current blockade with 4-aminopyridine (2 X 10(-4) M). The latter suggests the key role of the outward current increase in plateau phase shortening. It is further potentiated by high external K+ and Ca2+ as well as by ouabain 5 X 10(-7) M. It is concluded that simultaneous alteration of mechanical and electrical activity after rest might be related to accumulation of Ca2+ inside the cardiac cell and K+ outside it as the result of sodium pump inhibition in quiescent rabbit papillary muscle.

4-Aminopyridine↗
PubMed2003

Effects of epinephrine and phosphodiesterase III inhibitors on bupivacaine-induced myocardial depression in guinea-pig papillary muscle.

BACKGROUND: This study was designed to investigate the effects of epinephrine and the phosphodiesterase III inhibitors amrinone and milrinone on bupivacaine-induced myocardial depression in guinea-pig papillary muscles using an electrophysiological method. METHODS: Electrophysiological studies of the effects of bupivacaine, epinephrine, amrinone and milrinone in normal and high K(+) Tyrode's solution were measured with guinea-pig papillary muscles. Specifically, epinephrine, amrinone and milrinone reversal of bupivacaine-induced depression was measured. RESULTS: Bupivacaine reduced the action potential duration (APD), the maximum rate of rise of the AP (V(max)) and contractile force. Although epinephrine increased the contractile force similarly to amrinone and milrinone, it shortened the APD at 50% repolarization (APD(50)) and 90% repolarization (APD(90)). A high concentration of amrinone shortened APD, while milrinone did not affect APD except for a prolongation of APD(20). In high K(+) Tyrode's solution (25 mM), epinephrine, amrinone and milrinone increased the APD and the contractile force. Epinephrine reversed bupivacaine depression of APD and contractile force to control levels. Amrinone and milrinone restored not only the contractile force but also APD. There was an incomplete recovery of APD(50) for amrinone and the prolongation of APD(20) for milrinone. CONCLUSIONS: Our results suggest that bupivacaine decreases the Ca(+) current (I(Ca)) and Na(+) current (I(Na)). Epinephrine and amrinone may increase I(Ca) and the delayed outward current (I(k)), whereas milrinone may increase I(Ca). The profound cardiovascular depression caused by bupivacaine was effectively reversed by amrinone and milrinone in a manner similar to epinephrine.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1987

Effects of Bay k 8644 on the coronary vascular selectivity of the dihydropyridine Ca antagonists in the canine isolated, blood-perfused papillary muscle preparation.

Antagonism by Bay k 8644 of the coronary vasodilator and negative inotropic effects of Ca antagonists was simultaneously investigated in the canine isolated, blood-perfused papillary muscle electrically driven at 2 Hz. Drugs were given intraarterially. Continuously infused intraarterially, Bay k 8644 inhibited more predominantly the coronary vasodilator effects of the dihydropyridine Ca antagonists (nifedipine, nitrendipine, and nicardipine) than those of diltiazem and verapamil, or the negative inotropic effects of nifedipine and nitrendipine. The negative inotropic effects of nicardipine, diltiazem, and verapamil were not significantly affected by Bay k 8644. The dose ratio for producing a 50% decrease in developed tension of the papillary muscle over the dose for producing a 50% increase in coronary blood flow (which reflects vascular selectivity) were 41 for nitrendipine, 25 for nifedipine, 21 for nicardipine, 9 for diltiazem, and 7 for verapamil. During infusion by Bay k 8644, the ratio was small (2 to 6) and almost similar among all five Ca antagonists. These results indicate that Bay k 8644 antagonizes more effectively the coronary vasodilating effects of the dihydropyridine Ca antagonists, suggesting that there is a specific type of Ca channel on coronary vascular smooth muscles, through which the dihydropyridine Ca antagonists act.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1977

Aschoff bodies in operatively excised atrial appendages and in papillary muscles. Frequency and clinical significance.

Among 481 patients undergoing various mitral valve operations, Aschoff bodies were found in 40 (21%) of 191 operatively excised left atrial appendages, in four (2%) of 273 operatively excised left ventricular papillary muscles (1 per patient), and in one (6%) of 17 patients with both left atrial appendage and papillary muscle operatively excised. Of the total of 45 patients with Aschoff bodies, 44 preoperatively had mitral stenosis, and only one, a 10-year-old boy, had pure mitral regurgitation. Sinus rhythm was present in 38 (84%), and atrial fibrillation in seven (16%). Perioperatively, only one of the 45 patients with Aschoff bodies had clinical or laboratory stigmata compatible with acute rhematic fever, and 58% had an illness compatible with acute rheumatic fever at any time.

Adolescent↗