bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of ryanodine and caffeine on contractility, membrane voltage, and calcium exchange in cultured heart cells.
Authors: Rasmussen C A , Sutko J L , Barry W H
Published: June 2012

To investigate the mechanisms of action of ryanodine and caffeine, changes in mechanical and electrical activity caused by these agents were correlated with alterations in 45Ca fluxes and cell Ca contents in chick embryo ventricular cell monolayer cultures. Ryanodine (10(-10)-10(-5) M) irreversibly decreased contraction amplitude by 10-70% relative to control in a concentration-dependent manner with minimal effects on electrical activity. Ryanodine caused a slight decrease in rapid 45Ca uptake, but no change in total exchangeable calcium content or rapid 45Ca efflux. Caffeine (1-20 mM) caused a transient (less than 10 seconds) 5-12% increase in contraction amplitude followed by a sustained 9-76% decrease in contraction amplitude and a 10 mV decrease in diastolic membrane voltage. Caffeine caused a decrease in rapid 45Ca uptake, a decrease in total exchangeable calcium content, and an increase in rapid 45Ca efflux. These results suggest that caffeine produces a decrease in sarcoplasmic reticulum (SR) Ca2+ uptake, and/or an increase in SR Ca2+ release that eventually depletes the SR of Ca2+, presumably accounting for the negative inotropic effect. The ryanodine effects on contraction are more difficult to account for solely in terms of alterations of transsarcolemmal Ca2+ fluxes and Ca2+ contents. Our data indicate an important role for the SR in excitation-contraction coupling in cultured chick embryo ventricular cells and suggest that SR Ca2+ is part of the rapidly exchanging Ca2+ compartment noted in 45Ca flux studies.
Increased ischemia-reperfusion injury to the heart associated with short-term, diet-induced hypercholesterolemia in rabbits.
Authors: Tilton R G , Cole P A , Zions J D , Daugherty A , Larson K B , Sutera S P , Kilo C , Williamson J R
Published: June 2012

The effects of increased dietary cholesterol content on coronary vascular hemodynamics and endothelial cell transport function were assessed in isolated rabbit hearts during 3.5 hours of reperfusion after 30 minutes of global, no-flow ischemia. In control hearts from rabbits fed normal chow, perfusion pressure, left ventricular end-diastolic pressure, maximum +dP/dt, and the rate of intravascular clearance of radiolabelled albumin remained constant during 5 hours of continuous perfusion, while the mean transit time of radiolabelled albumin increased 1.6 X baseline. In ischemic hearts from rabbits fed normal chow, perfusion pressure increased 59% during reperfusion while left ventricular end-diastolic pressure and maximum +dP/dt returned toward control levels. The rate of intravascular clearance of radiolabelled albumin decreased 36%, and the mean transit time of albumin increased approximately 3 X baseline. Ischemia-reperfusion injury to the cardiac vasculature and musculature was markedly increased in hearts of rabbits fed chow supplemented with 2% cholesterol for 2-3 weeks compared to rabbits fed the same diet for a longer duration (5-16 weeks) or rabbits fed normal chow. Prior to ischemia, permeation of the coronary vasculature by albumin was increased twofold in rabbits fed cholesterol for 2-3 weeks while myocyte contractile function was normal relative to chow-fed controls or the group fed cholesterol for 5-16 weeks. These effects of acute cholesterol feeding precede occlusive atherosclerotic coronary artery disease and occur at plasma cholesterol concentrations one third of those in rabbits fed cholesterol for the longer duration.(ABSTRACT TRUNCATED AT 250 WORDS)
Characteristics of junctional regions between Purkinje and ventricular muscle cells of canine ventricular subendocardium.
Authors: Rawling D A , Joyner R W
Published: June 2012

The normal cardiac activation sequence requires propagation of the action potential from the subendocardial Purkinje network into the underlying ventricular muscle cells. This process occurs at specific junctional sites distributed over the endocardial surface of both ventricles. At these junctional sites, action potentials can be recorded from cells that appear to be interposed between the Purkinje cells and the ventricular muscle cells. The action potential upstrokes recorded from these "transitional" cells have characteristic double phases produced by electrotonic interactions with the Purkinje cells and the ventricular muscle cells. We have shown that these junctional regions in the canine subendocardium appear to be fixed anatomic sites with locations independent of the activation sequence of the Purkinje network. In addition, the activation delay between the Purkinje cells and the ventricular muscle cells at a junctional site and the patterns of the action potential upstrokes of transitional cells at a junctional site are independent of the activation sequence of the Purkinje network. We have also demonstrated that at some locations there are multiple Purkinje activation signals recorded with a surface electrode and that these multiple activation signals represent discrete groups of Purkinje cells, some of which contribute to the junctional process while others appear to be substantially uncoupled from neighboring Purkinje cell groups and the underlying transitional cells.
Inhibition of calcium influx in isolated adult rat heart cells by ATP depletion.
Authors: Haworth R A , Goknur A B , Hunter D R , Hegge J O , Berkoff H A
Published: June 2012

Using 45Ca, indo1, and quin2, calcium uptake was measured in isolated quiescent adult rat heart cells under different metabolic conditions. Exposure of cells in a medium containing 1 mM CaCl2 to rotenone and uncoupler resulted in adenosine triphosphate (ATP) depletion from 17.08 +/- 2.26 to 0.63 +/- 0.11 nmol/mg within 8 minutes, and the cells went into contracture. In this time, the cells lost 1.65 +/- 0.1 nmol Ca/mg of total rapidly exchangeable cellular calcium, and the level of free cytosolic calcium as measured by indo1 rose from 47.4 +/- 16.3 nM to 79.8 +/- 27.6 nM. The subsequent rate of rise of intracellular free calcium concentration was just 4 nM/min for at least 40 minutes. Therefore, we investigated the effect of ATP depletion on the rate of calcium entry. In cells loaded with sodium by ouabain treatment without calcium, the initial rate of calcium influx on calcium addition was inhibited by 82-84% when cellular ATP was depleted, as measured by 45Ca or indo1. Quin2 also showed a strong inhibition of calcium influx by ATP depletion, but itself also caused a strong inhibition of calcium influx. The rate of calcium influx declined even further in ATP-depleted cells after the initial influx: Between 1 and 12 minutes after calcium addition, the residual 45Ca uptake rate of the first minute was inhibited by an additional 90%. We conclude that ATP depletion per se does not quickly elevate cytoplasmic free calcium and that such an elevation is prevented by a very strong inhibition of the rate of calcium entry.
Finite element analysis of myocardial diastolic function using three-dimensional echocardiographic reconstructions: application of a new method for study of acute ischemia in dogs.
Authors: McPherson D D , Skorton D J , Kodiyalam S , Petree L , Noel M P , Kieso R , Kerber R E , Collins S M , Chandran K B
Published: June 2012

The effect of acute myocardial ischemia on the myocardial elastic modulus has been a matter of controversy. To evaluate this question, diastolic elastic modulus was assessed by finite element analysis of left ventricular geometry using three-dimensional echocardiographic reconstructions and right and left ventricular pressure recordings. Elastic properties were estimated before and after coronary occlusion in 6 open-chest dogs. Elastic modulus values were derived by means of a computer program that determined the global elastic modulus that best predicted the diastolic changes in left ventricular geometry. In the finite element analysis after coronary occlusion, two analyses were performed: one utilizing the control elastic modulus for all segments of the left ventricle and one in which ischemic (dyskinetic) segments were assigned a higher elastic modulus. Results showed that the control elastic modulus was a poor predictor of diastolic left ventricular expansion after coronary occlusion. The finite element analysis in which the ischemic segments were assigned a higher elastic modulus better predicted ischemic diastolic wall motion patterns. Error values (difference between predicted and actual left ventricular segmental diastolic motion) were: control, 1.9 +/- 0.3 mm (mean +/- SD), ischemia, 2.9 +/- 0.5 mm, and 2.2 +/- 0.4 mm using the stiffer elastic modulus for ischemic segments. Error values were significantly higher (p less than 0.05) under ischemic conditions when the control elastic modulus was uniformly applied compared with control and ischemia with dyskinetic segments assigned a higher elastic modulus. From these data, it is concluded that the myocardial diastolic elastic modulus is increased by ischemia and that this approach may allow clinical assessment of intrinsic muscle stiffness.
Dynamic stiffness measured in central segment of excised rabbit papillary muscles during barium contracture.
Authors: Shibata T , Hunter W C , Yang A , Sagawa K
Published: June 2012

The dynamic mechanical behavior of excised rabbit papillary muscles that had been tonically activated by replacing bathing Ca2+ with Ba2+ was studied. Steady activation was used to visualize the dynamic behavior of cardiac myofilaments more clearly than is possible during twitches, which are complicated by the kinetics of excitation-contraction coupling. To avoid artifacts due to damaged ends of the muscle, the length of a central segment, which was defined by 2 tungsten pins inserted through the muscle, was measured. To test the mechanical behavior of the contractured muscles (at 24 degrees C), the central segment length was sinusoidally oscillated (amplitude 1%) at 15 different frequencies (0.05-30 Hz). The dynamic stiffness of the central segment was calculated from the ratio of force response amplitude to length perturbation amplitude. At low frequencies (below 0.4 Hz), stiffness was approximately constant and reflected the force-length relation. However, in a localized range near 1 Hz, there was a distinct drop in the magnitude of dynamic stiffness to approximately half its low-frequency baseline. This range may reflect the dynamics of attachment and detachment of force generators. The frequency of minimum stiffness was consistent among all muscles (1.3 +/- 0.3 Hz). Moreover, no significant change in this frequency was found over the examined range of lengths (90-100% of the segment length that produced maximal developed force) and activation levels (Ba2+ concentration 0.3-1.0 mM). From 2 to 8 Hz, dynamic stiffness appeared to reflect force-velocity properties, but at higher frequencies, another elastic property emerged. At 30 Hz, stiffness was proportional to force, with an apparent series elasticity less than 1.8%. Even though the muscles had only moderate longitudinal inhomogeneity, quantitatively significant (35%) errors would have been introduced had the study relied on total muscle length instead of central segment length.
Mechanical determinants of maximum isotonic lengthening rate in rat left ventricular myocardium.
Authors: Zile M R , Gaasch W H , Wiegner A W , Robinson K G , Bing O H
Published: June 2012

The effects of changing loading conditions and inotropic state on maximum isotonic lengthening rate (+dL/dt, muscle lengths/sec) were examined in isolated rat myocardium. Physiologically sequenced contractions were studied in 18 left ventricular papillary muscle preparations (stimulation rate, 12/min). To study the effects of changing loading conditions, only one loading variable (preload, total load, or late load) was changed during each contraction, while the others were held constant. To study the effects of isoproterenol (10(-6) M) and temperature (28 vs. 33 degrees C) on maximum isotonic lengthening rate, preload and late load were held constant and +dL/dt was examined at a common total load. When preload was increased from 0.7 +/- 0.1 to 1.4 +/- 0.1 g/mm2, muscle length increased from 0.98 +/- 0.003 to 1.01 +/- 0.002 muscle lengths, the extent of shortening increased from 0.05 +/- 0.003 to 0.08 +/- 0.003 muscle lengths, but minimum length (0.93 +/- 0.01 muscle lengths) and +dL/dt (1.1 +/- 0.1 muscle lengths/sec) were unchanged. When total load was increased from 1.5 to 4.5 g/mm2, minimum length increased from 0.91 +/- 0.05 to 0.97 +/- 0.05 muscle lengths and +dL/dt fell from 1.4 +/- 0.1 to 0.5 +/- 0.1 muscle lengths/sec. Late load (the load borne by or applied to the muscle during isotonic lengthening) was altered by changing its magnitude (g/mm2) or time (milliseconds after stimulation) of application. As late load was increased from 1.4 +/- 0.02 to 2.1 +/- 0.3 g/mm2, +dL/dt increased from 1.3 +/- 0.2 to 2.1 +/- 0.3 muscle lengths/sec.(ABSTRACT TRUNCATED AT 250 WORDS)
Role of thyroid hormone in regulation of isomyosin composition, contractility, and size of heterotopically isotransplanted rat heart.
Authors: Korecky B , Zak R , Schwartz K , Aschenbrenner V
Published: June 2012

The role of thyroid hormone on the heart in terms of contractility, induction of growth, and selective synthesis of cardiac isomyosins was studied. After transplanting rat hearts from inbred hypothyroid donors into the abdomen of hypothyroid recipients of the same strain, two hearts were obtained in the same animal, both having reduced heart rate (200-250 bpm), decreased maximum rate of force, and high predominance of V3 isomyosin. The heart in situ carried a full load, while the transplant was denervated, beat isovolumically with minimum external work. After surgery, the recipient rats were put either on normal diet only (controls) or injected with a daily dose of T3 (average 200 micrograms/kg), which increased the heart rate to 340 bpm in 3 days (euthyroid level) and to 450 bpm in 7 days (hyperthyroid level). In T3-treated rats, the contractility of both hearts normalized in 7 days and showed hyperthyroid pattern in 14 days, while the mass of the in situ hearts increased to normal values in 7 days (+130 mg) and hypertrophied in 14 days (+340 mg), in contrast to the transplanted heart, which underwent atrophy (-90 mg and -210 mg) similar to that of control group (-225 mg). The predominant V3 isomyosin was completely reversed to V1 in two weeks in both hearts. Thus, T3 can neither stimulate cardiac growth nor can it attenuate the rate of atrophy in the denervated "nonworking" heart in spite of its direct effect on contractility and synthesis of isomyosins, which was similar to that observed in the in situ heart.
Contractile failure and high-energy phosphate turnover during hypoxia: 31P-NMR surface coil studies in living rat.
Authors: Bittl J A , Balschi J A , Ingwall J S
Published: June 2012

Cardiac failure appears rapidly during severe hypoxia and precedes a substantial reduction in adenosine triphosphate content. Reduced adenosine triphosphate turnover, in the presence of nearly normal content, may be the metabolic basis for contractile failure during hypoxia. To measure both the myocardial content and the turnover rates of high-energy phosphate compounds during hypoxia, we performed 31P-nuclear magnetic resonance studies by placing a surface coil directly over the left ventricle in intubated rats that were instrumented for hemodynamic measurements and ventilated with either 21, 10, or 8% O2. Normoxia produced a hemodynamic and metabolic steady state for 4 hours and hypoxia for at least 60 minutes. Under normoxic ventilation (n = 10, mean +/- SD), the arterial PO2 was 96 +/- 14, pH 7.38 +/- 0.11, and systolic blood pressure 96 +/- 8 mm Hg; under hypoxic ventilation with 10% O2 (n = 5), the arterial PO2 was 57 +/- 10, pH 7.39 +/- 0.09, and systolic pressure 68 +/- 10; and under hypoxic ventilation with 8% O2 (n = 5), the PO2 was 52 +/- 7, pH 7.37 +/- 0.04, and systolic pressure 51 +/- 4. Hypoxic ventilation with 10 or 8% O2 decreased the creatine phosphate content from 51.4 +/- 5.4 mumol/g dry wt to 39.3 +/- 5.4 and 45.6 +/- 4.1 and depressed adenosine triphosphate slightly from 25.0 mumol/g dry wt to 21.8 +/- 2.1 and 21.9 +/- 1.0, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
Mechanisms of closure of cardiac sodium channels in rabbit ventricular myocytes: single-channel analysis.
Authors: Grant A O , Starmer C F
Published: June 2012

We have examined the kinetics of closure of sodium channels using single-channel recordings in cell-attached and excised membrane patches of rabbit ventricular myocytes. Sodium-channel closure was dependent on membrane potential. The closing rate initially decreased with depolarization. The rate then passed through a minimum and increased at strongly depolarized potentials. We attempted to determine the separate voltage dependence of the deactivation and inactivation rate constants using the method of Aldrich, Corey, and Stevens. In a majority of experiments, the method did not give internally consistent results. As an alternative approach, batrachotoxin was used to remove inactivation and determine the voltage dependence of deactivation rate. The deactivation rate decreased with depolarization. To account for the increase in the closing rate at strongly depolarized test potentials, one must postulate voltage dependence of inactivation. The ensemble average current relaxed with a time course that was usually best described by the sum of two exponentials. The larger of the two rate constants that described the relaxation was strongly voltage-dependent, increasing with depolarization. The larger rate constant may reflect voltage-dependent inactivation. We found evidence of two possible mechanisms for the slow component of relaxation: 1) cardiac sodium channels may open repetitively during a given depolarizing epoch, and 2) channels may return from the inactivated state with low probability and burst for as much as 200 msec with open times that are longer than those during usual gating. The slow component appears to be more prominent in cardiac muscle than in nerve and may play an important role in the control of the action potential duration and the inotropic state of the heart.
Changes in atrial and ventricular refractoriness and in atrioventricular nodal conduction produced by combinations of vagal and sympathetic stimulation that result in a constant spontaneous sinus cycle length.
Authors: Inoue H , Zipes D P
Published: June 2012

The vagal nerves modulate adrenergic effects on sinus cycle length, atrioventricular (AV) nodal conduction, and refractoriness of atria and ventricles. We tested whether varying levels of vagal-sympathetic input could yield the same spontaneous sinus cycle length but also alter effective refractory periods of the right atrium, right ventricle, and left ventricle and AV nodal conduction times. Dogs anesthetized by alpha-chloralose were studied in the open-chest, neurally decentralized state. In 10 dogs, sinus cycle length was maintained constant during 3 levels of bilateral ansae subclaviae stimulation (4 msec, 3 mA at 1, 2, and 4 Hz) by titrating simultaneous bilateral vagal stimulation (varying pulse width and frequency). Each combination of ansae subclaviae-vagal stimulation yielded the same sinus cycle length as the control value, but refractory periods of right atrium and right and left ventricles shortened progressively as the frequency of ansae subclaviae stimulation increased. Atrioventricular nodal conduction time (AH interval) shortened in 2 dogs and lengthened in 3 dogs. His-Purkinje conduction time (HV interval) was unchanged. In 9 dogs, the effect of simultaneous unilateral ansae subclaviae stimulation at 2 Hz and ipsilateral vagal stimulation that yielded the same sinus cycle length were determined. Right-sided ansae subclaviae-vagal stimulation shortened refractoriness of right atrium and anterior left ventricle significantly. The AH interval lengthened in 1 dog. Left ansae subclaviae-vagal stimulation shortened the refractory periods of anterior and posterior left ventricle significantly and reduced the AH interval in 3 dogs. In 8 dogs, the effects of bilateral ansae subclaviae stimulation alone at 2 Hz, vagal stimulation alone at an intensity required to keep the sinus cycle length constant during ansae subclaviae stimulation, and simultaneous bilateral ansae subclaviae and vagal stimulation were tested. The right atrial refractory period was shortened significantly by ansae subclaviae stimulation alone and by vagal stimulation alone and was shortened further by simultaneous stimulation of both autonomic limbs. The right and left ventricular refractory periods were shortened by ansae subclaviae stimulation alone and by simultaneous stimulation of both limbs but tended to be prolonged by vagal stimulation alone and when added to ansae subclaviae stimulation. In 7 dogs, the effects of simultaneous stimulation of bilateral ansae subclaviae at 2 Hz and vagi at intensities that maintained the AH interval constant at an atrial pacing cycle length of 300 msec were determined.(ABSTRACT TRUNCATED AT 400 WORDS)
Voltage dependence of intracellular [Ca2+]i transients in guinea pig ventricular myocytes.
Authors: Barcenas-Ruiz L , Wier W G
Published: June 2012

[Ca2+]i transients, elicited by voltage-clamp depolarization of single guinea pig cardiac ventricular cells, were observed through use of the fluorescent Ca2+ indicator, fura-2. Individual cells, loaded with fura-2 either by internal perfusion or by exposure to fura-2/AM, were studied with the use of an inverted microscope that was equipped with ultraviolet epifluorescence illumination, an intensified silicon intensifier target camera, and a photomultiplier tube. Variation of membrane voltage and exposure of cells to verapamil (a Ca2+ channel blocker) and ryanodine (which was assumed to abolish selectively the release of Ca2+ from the sarcoplasmic reticulum) were used to investigate the cellular processes that determine the [Ca2+]i transient. The principal results of the study are: When appropriate methods are used, the properties of cytosolic fura-2 inside guinea pig cells are similar to those of fura-2 in solution, irrespective of the method of loading. The amplitude (at 100 msec) of verapamil-sensitive fluorescence transients elicited by pulse depolarization (range -30 to 80 mV) has a bell-shaped dependence on membrane voltage (maximum at 10 mV). Rapid, ryanodine-sensitive and verapamil-sensitive "tail transients" are elicited on repolarization from membrane potentials greater than 30 mV; their amplitude increases as the amplitude of the preceding pulse increases. The amplitude of slow fluorescence transients that are insensitive to verapamil and ryanodine increases continuously with membrane potential throughout the range -20 to 80 mV. The voltage dependence and pharmacology of the rapid transients elicited by pulse depolarization or by repolarization are consistent with their having arisen from Ca2+ released from the sarcoplasmic reticulum, via Ca2+-induced Ca2+ release.(ABSTRACT TRUNCATED AT 250 WORDS)
Control of cytosolic calcium activity during low sodium exposure in cultured chick heart cells.
Authors: Kim D , Okada A , Smith T W
Published: June 2012

We investigated the roles of sodium-calcium exchange, sarcoplasmic reticulum, and mitochondria in Cai homeostasis in cultured chick ventricular cells. Specifically, the influence of low sodium medium on contractile state, calcium fluxes, and cytosolic free [Ca] [( Ca]i) was examined. [Ca]i was measured using fura-2. Mean [Ca]i in control medium was 126 +/- 14 nM. Exposure of cells to sodium-free or sodium- and calcium-free medium (choline-substituted) resulted in contracture development, which returned toward the baseline level over 2-3 minutes. The Nao-free contracture was associated with a tenfold increase in [Ca]i (1,280 +/- 110 nM) followed by a gradual decrease to a level fourfold above control [Ca]i (460 +/- 58 nM). Nao- and Cao-free contracture was associated with a fivefold increase in [Ca]i (540 +/- 52 nM) followed by a rapid decrease to below 80 nM. Sodium-free medium failed to produce an increase in [Ca]i or contracture in cells preexposed to calcium-free medium, although caffeine, when subsequently added to sodium- and calcium-free medium, was able to elicit a transient increase in [Ca]i and contracture. Brief, 5-second preperfusion of cells with La3+ (1 mM) or EGTA (1 mM) abolished the Nao-free contracture and the increase in [Ca]i. In the presence of 20 mM caffeine, removal of Nao resulted in minimal changes in the resting position of the cell although 45Ca uptake and [Ca]i were increased in response to sodium-free medium; the subsequent decrease in [Ca]i was greatly slowed. Addition of caffeine during the relaxation phase of the sodium-free contracture produced an additional transient contracture and transient increase in [Ca]i. Ryanodine (1 microM) abolished this effect of caffeine. Caffeine or ryanodine abolished Nao- and Ca-free contracture. CCCP (2 microM), a potent oxidative phosphorylation inhibitor, did not significantly affect calcium efflux rate. In the presence of 2 microM CCCP, removal of sodium resulted in an augmented contracture signal and a rise in [Ca]i, followed by a slow decrease. We conclude that removal of extracellular sodium enhances transsarcolemmal entry of calcium via sodium-calcium exchange, but this effect alone does not lead to the development of sodium-free contracture. Calcium displaceable by lanthanum or EGTA appears to contribute to Nao-free or Nao- and Cao-free contracture. Studies using caffeine and ryanodine suggest that removal of Nao leads to release of calcium from the sarcoplasmic reticulum (presumably via calcium-induced calcium release).(ABSTRACT TRUNCATED AT 400 WORDS)
Proarrhythmic effects of an oxygen-derived free radical generating system on action potentials recorded from guinea pig ventricular myocardium: a possible cause of reperfusion-induced arrhythmias.
Authors: Pallandi R T , Perry M A , Campbell T J
Published: June 2012

Standard microelectrode techniques were used to study the effects of a free radical generating system on action potentials recorded from guinea pig ventricular myocardium. Free radicals were generated by mixing xanthine oxidase (0.02-0.04 mu/ml) with the superfusate-modified Locke's solution containing purine 2.3 mM. The system was validated by demonstrating that it could reduce cytochrome C at a rate of 15.9 +/- 1.5 mol/l/min. This rate was decreased to 3.0 +/- 0.3 (p less than 0.001) in the presence of superoxide dismutase (12 mg/100 ml), and the reaction was absent if xanthine oxidase and purine were premixed for 60 minutes prior to adding cytochrome C. Superfusion of guinea pig ventricular strips with the free radical generating system (20-30 minutes) resulted in a highly significant reduction in resting potential from -79.3 +/- 1.8 mV to -70.9 +/- 1.4 mV (p less than 0.0001, n = 6) and in action potential amplitude from 110.9 +/- 2.2 mV to 101.7 +/- 4.0 mV (p less than 0.0001). There was an accompanying fall in maximum rate of depolarization (Vmax) from 254.1 +/- 17.7 V/sec to 207.1 +/- 18.6 V/sec (p less than 0.01) and no significant change in action potential duration. These changes were accompanied by spontaneous activity in 3 of 6 preparations and reversed after 20-30 minutes washing in Locke's solution. They were largely abolished by adding superoxide dismutase (12 mg/100 ml) to the superfusate and completely absent if the xanthine oxidase and purine were premixed for 60 minutes before superfusing the myocardium. We conclude that the phenomena observed may contribute to the genesis of reperfusion arrhythmias.
Change in (dP/dt)max as an index of myocardial microvascular permeability.
Authors: Laine G A
Published: June 2012

We frequently study processes that alter microvascular permeability in the heart. Myocardial microvascular permeability has been estimated by determining the filtration independent reflection coefficient for beta-lipoprotein (sigma beta-LIPO). This technique requires the measurement of myocardial lymph flow rate and the lymph-to-plasma protein concentration ratio. Unfortunately, it is a nonsurvival procedure. An index of myocardial microvascular permeability was needed that could be determined in experimental preparations without sacrificing valuable chronically instrumented animals. We attempted to relate changes in myocardial microvascular permeability and myocardial edema formation to some index of myocardial performance. In 33 acute, anesthetized dogs (with normal or disrupted myocardial microvasculatures), we measured systemic arterial pressure, systemic venous pressure, coronary sinus pressure, left ventricular pressure, the maximum rate of change in left ventricular pressure (dP/dt)max, myocardial lymph flow rate, and myocardial extravascular fluid volume. Following an increase in coronary sinus pressure, the amount of edema fluid entering the myocardium varied as a function of myocardial microvascular permeability. Further, as the heart became edematous, (dP/dt)max changed with respect to time [delta(dP/dt)max/delta t]. Finally, a significant relation was found between sigma beta-LIPO and delta(dP/dt)max/delta t. Since coronary sinus pressure can be elevated and delta(dP/dt)max/delta t can be measured in chronic animals, this technique may be useful for evaluating myocardial microvascular permeability on a long-term survival basis.
Effects of quinidine sulfate on the balance among active and passive cellular properties that comprise the electrophysiologic matrix and determine excitability in sheep Purkinje fibers.
Authors: Arnsdorf M F , Sawicki G J
Published: June 2012

Quinidine is the most commonly used drug for the chronic treatment of ventricular arrhythmias, but it may be arrhythmogenic. Much information exists concerning quinidine's effects on active properties in cardiac tissues, but virtually nothing is known of its effects on passive properties. We studied the effects of quinidine, in a clinically relevant concentration, on the balance among active and passive cellular properties that comprise the electrophysiologic matrix that determines cardiac excitability. The multiple microelectrode method of intracellular-current application and transmembrane voltage recording was used in sheep Purkinje fibers to determine strength-duration and constant current-voltage relations as well as cable properties. A rapid, on-line computerized data analysis system tracked in time the alterations in the active and passive properties relevant to excitability. In normal fibers at [K+]o = 5.4 mM, quinidine increased cardiac excitability as manifested by a decrease in the current required to attain threshold and/or a downward shift in strength- and charge-duration relations by altering passive properties despite a depressed sodium system and a slowed conduction velocity. During washout, excitability and passive properties remained altered despite a return of descriptive action potential parameters such as the resting potential, the maximum rate of rise of phase 0, overshoot, and the action potential duration to or nearly to normal. At [K+]o = 8.0 mM, quinidine could either increase or decrease excitability; net excitability depends on the balance between altered passive properties and the depressed sodium system. The results explain, in part, the antiarrhythmic actions and arrhythmogenic potential of quinidine. The data for quinidine and other antiarrhythmic drugs are interpreted in terms of the electrophysiologic matrix, which we believe has important advantages over traditional hierarchical classifications.
Mechanism of histamine actions in human coronary arteries.
Authors: Toda N
Published: June 2012

Helical strips of human coronary arteries contracted in response to histamine concentration dependently, they relaxed with low concentrations and contracted with high concentrations. Treatment with cimetidine potentiated contraction in the strips with intact and damaged endothelium to a similar extent and attenuated relaxation. Removal of endothelium abolished relaxation and potentiated contraction in the cimetidine-treated strips. Methylene blue increased the contractile response to histamine in the strips with endothelium but did not alter the response in the damaged-endothelium strips. Histamine-induced relaxations in the intact strips were suppressed or abolished by treatment with ETYA, AA861, a lipoxygenase inhibitor, and by chlorpheniramine but were unaffected by indomethacin. Chlorpheniramine also abolished amine-induced contraction. It may be concluded that histamine-induced contraction in human coronary arteries is mediated by H1 receptors in smooth muscle, and relaxation is mediated by H2 receptors in smooth muscle and H1 receptors in endothelium. Also, stimulation of the endothelial H1 receptor liberates vasodilator substance and possibly activates smooth muscle guanylate cyclase to accumulate cellular cyclic guanosine monophosphate.
Development changes in the human cardiac isomyosin distribution: an immunohistochemical study using monoclonal antibodies.
Authors: Bouvagnet P , Neveu S , Montoya M , Leger J J
Published: June 2012

With monoclonal antibodies (Mab) specific for myosin heavy chain (MHC) isozymes, we have investigated the isomyosin content of atrial, ventricular and conductive fibers of 19 human fetuses (ranging from 14-36 weeks of gestation) and 3 newborns (2 days-2 weeks). In addition, the conduction system of 2 human adult hearts was studied. The fetal atrium is composed mostly of alpha-MHC during the first 23 weeks of gestation. beta-MHC is already expressed as traces at 14 weeks of gestation, and its expression increases progressively until birth, resulting in a great augmentation in beta-MHC. During this course, beta-MHC always predominates in certain areas (the crista terminalis and the interatrial septum) but not in other areas (the auricles). Preceding birth, the fetal ventricle is composed mostly of beta-MHC. From 14 weeks of gestation to birth, alpha-MHC is expressed in very rare fibers. Then, after birth, a large number of fibers simultaneously synthesize alpha-MHC. The AV node and His bundle system were labelled with anti-alpha and anti-beta Mab in fetal, newborn, and adult hearts with a double gradient of distribution: spatial (a higher proportion of alpha-containing fibers in the AV node than in the distal portion of the bundle of branches) and temporal (a higher proportion of alpha-containing fibers at a given point in fetal development than in the adult heart). One of the twenty-five hearts studied had an isomyosin distribution pattern not accorded to its age. Interestingly, it was clinically diagnosed as having idiopathic hypertrophic cardiomyopathy.
Effect of age on the development of cardiac hypertrophy produced by aortic constriction in the rat.
Authors: Isoyama S , Wei J Y , Izumo S , Fort P , Schoen F J , Grossman W
Published: June 2012

To test the hypothesis that the capacity to develop left ventricular (LV) hypertrophy might diminish with advancing age, we examined the hypertrophic response to ascending aortic constriction in 3 groups of adult Fischer 344 rats (9 months, 18 months, and 22 months of age). Aortic constriction was created so that aortic cross-sectional areas would be the same for the 3 groups of rats. Four weeks after imposition of aortic constriction, there was no significant difference in peak LV pressure, peak-to-peak and mean systolic pressure gradients between left ventricle and aorta, cardiac output, LV minute work, or cross-sectional area of the aortic constrictions in the 3 groups. In 9-month-old aortic-constricted rats, LV dry wt (LVDW)/body wt, LVDW/tibial length, and myocyte width increased by 23% (p less than 0.01), 14% (p less than 0.01), and 27% (p less than 0.01), respectively, compared with sham-operated rats. In contrast, in 18-month-old and 22-month-old aortic-constricted rats, LVDW/body wt and LVDW/tibial length were unchanged compared with sham-operated controls, and increases in myocyte width were only modest 4 weeks following constriction. RNA concentration in the myocardium 5 days after constriction increased by 21% (p less than 0.001) in 9-month-old rats but showed no significant rise in 18-month-old rats. These results suggest that advancing age is associated with a diminished capacity to develop myocardial hypertrophy in response to acute pressure overload and that a reduced ability to synthesize protein may be one of the major contributing factors to a diminished capacity for hypertrophy in advanced age.
L-carnitine treatment improves cardiac performance and restores high-energy phosphate pools in cardiomyopathic Syrian hamster.
Authors: Whitmer J T
Published: June 2012

Hamsters with either the dilated (BIO 53.58) or hypertrophic (BIO 14.6) form of cardiomyopathy and an inbred control strain of hamster (F1B) were treated for 6 months with high-dose L-carnitine (1 g/kg/day i.p.). After treatment, the animals were killed and their hearts perfused by the isolated working technique. Mechanical performance (as indicated by the double product of heart rate and left ventricular [LV] peak systolic pressure) of both carnitine-treated cardiomyopathic groups was increased significantly above their respective sham-treated groups. Associated with these increases in mechanical performance were significant increases in both peak-positive LV dP/dt (index of contractility) and peak negative dP/dt (index of relaxation) in both carnitine-treated myopathic groups. Serum carnitine levels were increased 10-15 times within 2 hours after injection of L-carnitine in all 3 groups. Myocardial free-carnitine levels were increased twofold in both control and dilated myopathic hearts above their respective sham-treated groups, restoring the level in the dilated hearts comparable to those of controls. Myocardial carnitine levels in the hypertrophic group were not significantly affected by treatment. Total high-energy phosphate stores, i.e., ATP plus creatine phosphate, were restored to control levels by L-carnitine treatment in both cardiomyopathic groups. Levels of the breakdown products of ATP were maintained primarily in the more readily convertible adenosine diphosphate and adenosine monophosphate forms in all three treated groups. These changes resulted in significantly higher ratios of (ATP)/(ADP + AMP + adenosine) and (creatine phosphate)/(creatine) in the treated hearts. This is the first study demonstrating that high-dose L-carnitine treatment results in improved cardiac performance and increased myocardial total high-energy phosphate stores in the Syrian hamster model with one of two distinct forms of cardiomyopathy, i.e., dilated or hypertrophic. The mechanisms for these effects of exogenous L-carnitine treatment cannot be totally explained by changes in oxidative energy metabolism.
Pertussis toxin-insensitive phosphoinositide hydrolysis, membrane depolarization, and positive inotropic effect of carbachol in chick atria.
Authors: Tajima T , Tsuji Y , Brown J H , Pappano A J
Published: June 2012

Muscarinic agonists can stimulate rather than inhibit cardiac muscle in some preparations. In left atria from hatched chicks, treatment with pertussis toxin reversed the membrane action of carbachol from hyperpolarization to depolarization and reversed the inotropic effect of carbachol from negative to positive. Acetylcholine also depolarized the membrane and increased the force of contraction in atria from pertussis-toxin-treated chicks although oxotremorine did not. These cholinergic responses were blocked by atropine but not by adrenoceptor antagonists, suggesting that they are mediated via muscarinic receptors and are not due to actions of endogenously released catecholamines. Muscarinic receptor stimulation leads to two distinct biochemical responses in chick atria: inhibition of adenylate cyclase and activation of phosphoinositide (PI) hydrolysis. The former is lost in atria from pertussis-toxin-treated chicks, whereas the PI response persists. The pharmacologic characteristics of the PI response resemble those of the depolarization and positive inotropic response. Both are insensitive to blockade by pertussis toxin, require high concentrations of carbachol, and are elicited by acetylcholine but not by oxotremorine. The present study suggests that muscarinic agonist-induced PI turnover may be responsible for the membrane depolarization and positive inotropic effects of carbachol and acetylcholine; that an increase in Na+ conductance underlies these responses; and that it is stimulated either by an increase of intracellular calcium mobilized by inositol triphosphate and/or by activation by protein kinase C.
Effect of endogenously produced leukotrienes and thromboxane on renal vascular resistance in rabbit hydronephrosis.
Authors: Albrightson C R , Evers A S , Griffin A C , Needleman P
Published: June 2012

Ureteral obstruction in rabbits is characterized by mononuclear cell invasion of the renal cortex and proliferative fibrosis that is associated with exaggerated prostaglandin synthesis in response to vasoactive and inflammatory cell agonists. In this investigation, we studied the effects of the chemotactic peptide N-formylmethionyl-leucyl-phenylalanine (fMLP) and bradykinin (BK) on eicosanoid synthesis and renal vascular resistance in the ex vivo perfused hydronephrotic kidney (HNK). Administration of fMLP resulted in the dose-dependent synthesis of leukotrienes, thromboxane A2 (TXA2), prostaglandin E2 (PGE2), and prostacyclin (PGI2). Peptidoleukotriene synthesis was monitored by specific radioimmunoassay and by guinea pig ileum bioassay and it was then validated by inhibition of the ileal contractile activity with the peptidoleukotriene receptor antagonist FPL-55712. The leukotrienes produced were identified as LTB4, LTC4, LTD4, and LTE4 by comigration with authentic standards on reverse phase high-performance liquid chromatography (RP-HPLC) and by ultraviolet spectroscopy. BK administration stimulated the synthesis of TXA2, PGE2, and PGI2 but not the synthesis of leukotrienes, in contrast to the results with fMLP, suggesting the involvement of different cell types. Administration of fMLP to the HNK also resulted in a renal vasoconstriction that was partially inhibited by FPL-55712 and that was completely inhibited by the thromboxane synthase inhibitor OKY-1581. Consistent with this result, exogenous administration of LTC4 resulted in the synthesis of TXA2 and in a renal vasoconstriction that was inhibited by either FPL-55712 or OKY-1581.(ABSTRACT TRUNCATED AT 250 WORDS)
Calcium and magnesium transport by in situ mitochondria: electron probe analysis of vascular smooth muscle.
Authors: Broderick R , Somlyo A P
Published: June 2012

The extent, time course, and reversibility of mitochondrial Ca2+ uptake secondary to cellular Ca2+ influx stimulated by massive Na+ efflux were evaluated by electron probe microanalysis of rabbit portal vein smooth muscle. Strips of portal vein were Na+ loaded for 3 hours at 37 degrees C in a K+-free 1 mM ouabain solution, after which rapid Na+ efflux was induced by washing with a Na+-free K+-Li+ solution (1 mM ouabain). Li+ washing Na+-loaded portal vein produced a large transient contraction accompanied by an increase (over 100-fold) in mitochondrial Ca2+ and also significant (p less than 0.05) increases in phosphorus and Mg2+. The Ca2+ loading of the mitochondria was reversed during prolonged Li+ wash, and by 2 hours, mitochondrial Ca2+, Mg2+, and phosphorus had returned to control levels. The maximal contractile response to stimulation remained normal, demonstrating that pathologic Ca2+ loading of mitochondria is reversible in situ and compatible with normal maximal force developed by the smooth muscle. Mitochondrial Ca2+ and phosphorus uptake were reduced but still significant when the Li+ wash contained 0.2 mM Ca2+ or when ouabain was omitted. The fact that mitochondrial Ca2+ loading accompanied submaximal contractions during 0.2 mM Ca2+-Li wash suggests "supranormal" affinity of mitochondria for Ca2+ and may be due, in part, to reverse operation of the mitochondrial Na+-Ca2+ exchanger. Mitochondrial Ca2+, Mg2+, and phosphorus uptake were eliminated when the Li+ wash was performed at 2 degrees C or when the wash contained no Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)
Attenuation of reflex forearm vasoconstriction by alpha-human atrial natriuretic peptide in men.
Authors: Takeshita A , Imaizumi T , Nakamura N , Higashi H , Sasaki T , Nakamura M , Kangawa K , Matsuo H
Published: June 2012

This study examined whether atrial natriuretic peptide (ANP) modulates reflex forearm vasoconstriction in humans. Synthetic alpha-human ANP (alpha-hANP) was infused at a rate of 0.03 microgram/kg/min in 8 healthy men (mean age 23 +/- 0.7 years, mean +/- SEM). The alpha-hANP decreased systolic blood pressure and central venous pressure (CVP) but did not significantly alter resting heart rate and forearm vascular resistance (FVR). The magnitudes of reflex increases in FVR during lower body negative pressure (LBNP) at -110, -20, and -40 mm Hg were less during infusion of alpha-ANP than those magnitudes during infusion of saline solution. The slope of the regression line relating changes in CVP and those in FVR was less during infusion of alpha-hANP than the slope during infusion of saline solution. Forearm vascular responses to intra-arterial infusion of norepinephrine at doses of 100, 200, and 500 ng/min did not significantly differ during infusion of alpha-hANP and saline solution. These results suggest that alpha-hANP attenuates cardiopulmonary baroreflex control of FVR in normal men.
Sex differences in peripheral vascular adrenergic receptors.
Authors: Freedman R R , Sabharwal S C , Desai N
Published: June 2012

Although the incidence of many vascular diseases differs in men and women, sex differences in vascular physiology have not been extensively examined in human in vivo studies. The present study compared finger blood flow responses of normal men and women with brachial artery infusions of adrenergic agonists and with other neurally and nonneurally mediated procedures. In response to phenylephrine and clonidine, men showed significant dose-related vasoconstriction while women did not. In response to isoproterenol, men showed significant dose-related vasodilation while women did not. There were no sex differences in response to intra-arterial nitroglycerin or digoxin or to reactive hyperemia, procedures that do not act through adrenergic receptors. These data show that the sensitivity and/or density of peripheral vascular adrenergic receptors is lower in women than in men. There were no sex differences in response to reflex vasoconstriction or to intra-arterial tyramine, suggesting that neurally released norepinephrine acts at alpha-adrenergic receptors that are spatially removed from those that respond to circulating catecholamines.