bluuebunny/crossref_metadata_2025 huggingface dataset:
Canine cardiac sarcolemmal vesicles demonstrate rapid initial Na(+)-Ca2+ exchange activity.
Authors: Gruver C L , Katz A M , Messineo F C
Published: June 2012

To identify a rapid, uninhibited rate of exchange activity, we investigated in canine sarcolemmal vesicles the rapid kinetics of Na(+)-Ca2+ exchange. Sarcolemmal vesicles were incubated in 160 mM NaCl and 20 mM HEPES at 25 degrees C (pH 7.4) and actively loaded with 45Ca2+ for 2 minutes by Na(+)-Ca2+ exchange. After further uptake was inhibited by dilution into 0.15 mM Na(+)-free EGTA, sarcolemmal vesicles were immobilized on a rapid filtration apparatus that allowed millisecond resolution of 45Ca2+ fluxes. In the presence of external NaCl (Na+o) but not other monovalent cations (i.e., K+, Li+), a biphasic pattern of Ca2+ release was observed--an initial brief and rapid rate of Ca2+ release followed by a second slower, prolonged phase of Ca2+ release. Semilogarithmic plots of sarcolemmal Ca2+ content versus time were not linear but were consistent with a biexponential rate of Na+o-induced Ca2+ release during the first several seconds of the exchange reaction. The fast phase of Na+o-stimulated Ca2+ release was several thousand-fold more rapid than that in the absence of Na+o. Both phases of Ca2+ release showed a similar Na+o dependence (Km, approximately 12 mM) with evidence of a positive cooperative effect of Na+. Vmax of the fast and slow phases were approximately 37.0 and approximately 0.76 nmol/mg/sec, respectively. Using rapid-reaction techniques, we demonstrated in the present study that the initial velocity of sarcolemmal Na(+)-Ca2+ exchange activity is greater than previously reported in sarcolemmal vesicles and that this exchange process exhibits complex rate behavior with a biphasic pre-steady state kinetic pattern.
Force and velocity of sarcomere shortening in trabeculae from rat heart. Effects of temperature.
Authors: de Tombe P P , ter Keurs H E
Published: June 2012

The effect of temperature on the force-sarcomere velocity relation (20 degrees, 25 degrees, and 30 degrees C) and maximum velocity of sarcomere shortening (Vo; range 15 degrees-35 degrees C) was studied in trabeculae from rat heart. Sarcomere length and Vo were measured by laser diffraction techniques. Sarcomere length and sarcomere velocity, determined from each of the first-order diffraction lines, differed by less than 4%. Slack sarcomere length in the trabeculae appeared to be 1.9 microns. Isovelocity release techniques were used to obtain sarcomere velocity and Vo directly. Sarcomere velocity was measured at SL = 1.9-2.0 microns for elimination of contributions of parallel elastic force and restoring force to the external load of the sarcomeres. Peak twitch force development (Fo) was maximal (Fo-max) at 25 degrees C at [Ca2+]o = 1.5 mM. Lowering of the temperature below 25 degrees C led to development of spontaneous sarcomere activity and depression of Fo; both responses could be prevented by the addition of 0.5 mM procaine. Increase of temperature above 25 degrees C reduced twitch duration and Fo. Hill's rectangular hyperbola fitted the force-velocity data if the load during shortening was less than 70% of Fo. Vo appeared to be independent of the level of activation at all temperatures when Fo was maintained above 90% of Fo-max, either by an increase of [Ca2+]o (to 3.0 mM) or by paired pulse stimulation. Vo increased with increasing temperature; the parameter a, calculated from force-velocity relations measured at 20 degrees, 25 degrees, and 30 degrees C, decreased with increasing temperature. The Arrhenius plot of Vo was studied in detail over a wider temperature range (15 degrees-35 degrees C) and in smaller temperature increments. The relation was linear between 18 degrees and 33 degrees C; the observed Q10, defined as the ratio of Vo measured at temperature (T) over Vo at T-10 degrees C, was 4.6 A Q10 of 4.6 for Vo is consistent with the reported temperature dependence of rat cardiac actin-activated myosin ATPase, which suggests that the same reaction step may limit the activity of the enzyme in vitro and during shortening of the cardiac sarcomeres at zero external load.
Limitation of myocardial infarct size by superoxide dismutase as an adjunct to reperfusion after different durations of coronary occlusion in the pig.
Authors: Näslund U , Häggmark S , Johansson G , Marklund S L , Reiz S
Published: June 2012

Superoxide dismutase (SOD) has been documented to limit myocardial infarct size in the richly collateralized dog heart. This study was designed to explore this concept in a low-collateralized animal model. A blind, randomized, placebo-controlled protocol was used in 65 pentobarbital-anesthetized pigs subjected to closed-chest left anterior descending coronary artery occlusion for 30 (n = 22), 60 (n = 22), and 90 (n = 14) minutes followed by reperfusion up to 24 hours from the start of occlusion. Another seven control pigs were subjected to 24 hours of permanent occlusion. A total dose of 9 mg/kg bovine CuZn SOD was administered as a bolus injection immediately before reperfusion followed by a 1-hour infusion. Infarct size was assessed by tetrazolium staining. Myocardium at risk and collateral flow were determined by using cerium-141-labeled microspheres (15 microns) during the occlusion. After 30 minutes of occlusion, infarct sizes in placebo versus SOD-treated animals were 45.5 +/- 15.7% vs. 23.8 +/- 15.6% of myocardium at risk (p = 0.007). The corresponding values after 60 minutes of occlusion were 78.6 +/- 9.3% vs. 66.9 +/- 14.6% (p = 0.035). SOD administered after 90 minutes of occlusion did not limit infarct size (88.5 +/- 4.8% vs. 92.3 +/- 5.2%). Twenty-four hours of coronary occlusion resulted in infarction of 92.4 +/- 4.2% of myocardium at risk. (All values are mean +/- SD.) Ventricular fibrillation occurred in only nine pigs distributed equally between SOD and placebo. The results indicate that CuZn SOD has the potential to further improve the myocardial salvage established by reperfusion of an ischemic pig heart territory. However, the narrow time window for limiting infarct size in the pig by reperfusion is not much extended by SOD.
Regulatory proteins in hamster cardiomyopathy.
Authors: Malhotra A
Published: June 2012

We have shown in genetic myopathic hamsters that cardiac myofibrillar ATPase regulation by calcium is altered and that there are shifts in myosin isozyme distribution (V1----V3) suggesting abnormalities in multiple components of the contractile apparatus. To focus more on the regulatory proteins (troponin and tropomyosin), individual proteins of the skeletal and cardiac actomyosin system were reconstituted under controlled conditions. In this way, myosin plus actin and troponin-tropomyosin from the normal and myopathic animals could be studied enzymatically. The proteins were isolated from the skeletal or cardiac muscle of random-bred control and cardiomyopathic hamsters (BIO 53:58) at 7 months of age. Sodium dodecyl sulfate gel electrophoretic patterns indicated differences in the troponin I and troponin C regions of myopathic skeletal muscle, but cardiac samples from control and myopathic hamsters showed similarities in their mobilities. This suggests the possibility of different cardiac isozymes in the regulatory protein complex, as reported in our previous studies of cardiac myosin in cardiomyopathy. Calcium sensitivity was markedly decreased in the actomyosin reconstituted with troponin-tropomyosin from skeletal as well as cardiac muscle from myopathic animals. In summary, our data show that the regulatory proteins in skeletal and cardiac muscle of the myopathic hamsters have decreased inhibitory action on Mg2(+)-actomyosin ATPase activity. This loss of calcium regulation along with shifts in cardiac myosin heavy chain may be partially responsible for the impaired cardiac function in the hearts of myopathic hamsters.
Sexual dimorphism in vasopressin and cardiovascular response to hemorrhage in the rat.
Authors: Crofton J T , Share L
Published: June 2012

There is evidence for sex-related differences in the cardiovascular actions of vasopressin. Furthermore, receptors for the gonadal steroid hormones are located in centers in the brain involved in the control of vasopressin release and in cardiovascular regulation. We have, therefore, examined the effects of hemorrhage on mean arterial blood pressure, the plasma vasopressin concentration, and plasma renin concentration in conscious male and female rats. In preliminary experiments, no differences were found in blood and plasma volumes with respect to either sex or phase of the estrous cycle. In separate experiments, rats were subjected to two hemorrhages of 10% of blood volume, separated by an interval of 15 minutes. There were no substantial gender- or cycle-related differences in the ability of hemorrhaged rats to maintain mean arterial blood pressure or increase plasma renin concentration. The increase in plasma vasopressin concentration was greater in proestrous females than in males after the first hemorrhage and in diestrous, proestrous, and metestrous females than in males after the second hemorrhage. Pretreatment with a V1-receptor antagonist was without statistically significant effect on the mean arterial blood pressure responses in males, but it impaired blood pressure compensation in females. There are, then, gender- and cycle-related differences in vasopressin responses to hemorrhage, and vasopressin appears particularly important for blood pressure compensation to hemorrhage in female rats.
Effects of prolonged hypoxia on adenylate cyclase activity and beta-adrenergic receptors in pulmonary and systemic arteries of the rat.
Authors: Shaul P W , Muntz K H , DeBeltz D , Buja L M
Published: June 2012

Prolonged hypoxia causes pulmonary hypertension but no change in systemic vasomotor tone. In an effort to define the mechanisms involved, we determined the effects of 3 and 7 days of hypoxia on adenylate cyclase activity and beta-adrenergic receptor binding characteristics in pulmonary and systemic arteries in an adult rat model of hypoxic pulmonary vasoconstriction produced by hypobaria. Basal and stimulated adenylate cyclase activity were measured in crude membrane preparations by radioimmunoassay for cyclic AMP. Basal enzyme activity in pulmonary arteries did not change with hypoxia, whereas in systemic arteries it increased 3.5- and 5.3-fold following 3 and 7 days of hypoxia, respectively. GTP-stimulated activity in pulmonary arteries also did not change, but in systemic arteries it increased 7.1- and 5.5-fold. Isoproterenol-stimulated activity in pulmonary arteries was decreased to 49% of control-stimulated activity following 3 days but was similar to control-stimulated activity after 7 days of hypoxia; in systemic arteries it increased 5.6- and 4.6-fold. Sodium fluoride-stimulated activity in pulmonary arteries was unchanged, whereas in systemic arteries it increased 3.8- and 5.3-fold. In contrast, forskolin-stimulated activity, which also was not altered in pulmonary arteries, was increased by only 85% and 71% in systemic arteries. beta-Adrenergic receptors were studied with [125I]iodocyanopindolol. Seven days of hypoxia decreased receptor density by 37% and 57% in the pulmonary and systemic arteries, respectively. Receptor affinity for agonists was not altered. Thus, despite downregulation of beta-adrenergic receptors in both artery types, prolonged hypoxia has no sustained effect on adenylate cyclase activity in pulmonary arteries, whereas enzyme activity in systemic arteries is markedly increased.(ABSTRACT TRUNCATED AT 250 WORDS)
Spectral analysis of canine epicardial electrogram. Short-term variations in the frequency content induced by myocardial ischemia.
Authors: Mor-Avi V , Akselrod S
Published: June 2012

Power spectra of epicardial electrograms were studied in 13 anesthetized dogs subjected to occlusion of the left anterior descending coronary artery. Electrograms were obtained from a bipolar electrode placed on the epicardial surface of the left ventricle and recorded before and after coronary occlusion. After digitization, power spectra of the first and every 50th subsequent waveform were evaluated and compared with the power spectrum of the average waveform obtained from the baseline recording. In particular, we examined variations in relative power content in three frequency ranges: 150-250 Hz, previously shown to be directly affected by myocardial ischemia; 40-150 Hz, presumably corresponding to the fine notches and slurs on the body surface QRS; and 2-40 Hz, the low-frequency range. Apart from a mild initial rise during the first 50 heart beats, the power in the high-frequency range gradually decreased, reaching 5% of the control value at wave 500. The power in the mid-frequency range showed a monotonous decrease after the occlusion and reached 16% of the control. The power in the low-frequency range showed a gradual buildup to 140% of the control after 500 heart beats. Therefore, ischemia causes a shift of the high-frequency spectral components of the local electrographic waveform to lower frequencies. Our findings and the fact that body surface ECG is produced by spatial summation of local electric potentials over the different regions of the myocardial tissue may explain two previously described effects of acute myocardial ischemia on the body surface ECG complex. First, local loss of spectral components in the range 150-250 Hz may produce a zone of reduced amplitude within a QRS complex band-pass filtered in this range. Second, displacement of power in the frequency domain may suggest an explanation to the increased incidence of visible notches and slurs on the surface QRS complex, characteristic to various myocardial pathologies.
Myocardial effects of selective alpha-adrenoceptor blockade during exercise in dogs.
Authors: Guth B D , Thaulow E , Heusch G , Seitelberger R , Ross J
Published: June 2012

To study the effect of selective alpha 1- or alpha 2-adrenergic blockade on the myocardial contractile and chronotropic response to exercise, 29 dogs were chronically instrumented with a sonomicrometer for measuring myocardial wall thickness and a micromanometer for measuring left ventricular pressure. During treadmill exercise, either the selective alpha 1-blocker prazosin (80 micrograms/kg, n = 12) or the alpha 2-blocker idazoxan (80 micrograms/kg, n = 8) was infused into the left atrium beginning 2-3 minutes after the onset of exercise. alpha 1-Adrenoceptor blockade, like alpha 2-adrenoceptor blockade, was found to cause significant increases in systolic wall thickening, thickening velocity, heart rate, and left ventricular contractility, indicating an increase in inotropic state that was comparable to that with alpha 2-adrenoceptor blockade. Preventing the decrease in aortic blood pressure after selective alpha 1-blockade by using either systemic angiotensin II infusion (n = 6) or inflation of an intra-aortic balloon (n = 6) did not prevent the observed increases in wall thickening, heart rate, and left ventricular contractility. In four of the dogs treated with prazosin, the norepinephrine concentration in the coronary sinus was found to more than double after alpha 1-blockade. beta-Adrenergic blockade (propranolol, 1.0 mg/kg) prevented the increased contractile and chronotropic state caused by alpha 1- or alpha 2-blockade. Selective alpha-adrenergic blockade during adrenergic activation by intravenous norepinephrine infusion, in contrast to exercise, had no effect on wall thickening, heart rate, or left ventricular contractility. These data indicate that selective alpha 1-adrenergic blockade, like selective alpha 2-adrenergic blockade, causes a significant augmentation of heart rate and left ventricular contractility in the dog during dynamic exercise. These data are consistent with the hypothesis that this occurs through a presynaptic disinhibition of neural norepinephrine release mediated by a prejunctional alpha 1-adrenoceptor.
Actions of adenosine on nitro blue tetrazolium deposition and surface pH during intestinal reperfusion injury.
Authors: Kaminski P M , Proctor K G
Published: June 2012

Mesenteric arteries supplying an intestinal segment were occluded for 5 minutes and then released. During reperfusion, two series of measurements were made with various substances topically applied to the extraluminal surface. In the first series, reduced nitro blue tetrazolium (NBT) was extracted from tissue and measured spectrophotometrically, as an index of oxidative damage. In the second series, mucosal and serosal surface pH was measured as an index of the functional ability to maintain ion gradients. In control conditions, NBT deposition averaged 55-63 micrograms/g tissue. After 60 and 120 minutes of reperfusion, NBT was elevated to 446-479 micrograms/g, which was approximately half as large as the NBT increment (846 micrograms/g) produced by a 15-minute application of xanthine plus xanthine oxidase to well-perfused tissue. As expected, NBT levels were significantly lower (299 micrograms/g) in tissue that was continuously suffused with superoxide dismutase (SOD) plus catalase (CAT) before occlusion and during reperfusion. Similar NBT levels (274 micrograms/g) were observed after reperfusion in animals that were fed a diet supplemented with the antioxidant vitamin E for 4-6 weeks. These observations affirm that some, but not all, NBT deposition after reperfusion can be attributed to oxyradicals. However, with exogenous adenosine (ADO) applied for the first 30 minutes after occlusion, NBT was elevated to 174 micrograms/g after 60 minutes, which was only half as large as the increment with SOD plus CAT, even though those substances were continuously applied. The opposite effect was produced by an ADO receptor antagonist, 8-phenyltheophylline; NBT was increased to 516 micrograms/g.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of changes in circulating blood volume on cardiac output and arterial and ventricular blood pressure in the stage 18, 24, and 29 chick embryo.
Authors: Wagman A J , Hu N , Clark E B
Published: June 2012

We studied the hemodynamic effects of changing volume loading in the chick embryo, before autonomic innervation, to test the hypothesis that the Frank-Starling mechanism functions in the embryonic myocardium. Dorsal aortic blood velocity was measured by pulsed Doppler. Heart rate and aortic diameter were also measured to calculate cardiac output and stroke volume index. Vitelline arterial and ventricular pressures were measured with a servo-null micropressure system in stage 24 embryos. Infusing isotonic solution intravenously resulted in linear increases in stroke volume index for stages 18 (y = 388x + 6.89), 24 (y = 466x + 7.86), and 29 (y = 549x + 4.96). The slopes and intercepts were statistically the same for all three stages. Similar volume loading in stage 24 embryos initially increased mean arterial pressure linearly, but at higher loading conditions, the rate of rise lessens. Thus, volume loading resulted in a decrease in vascular resistance. Withdrawing blood from stage 24 embryos resulted in a decrease in ventricular peak systolic and end-diastolic pressures. With reinfusion of the blood, systolic and end-diastolic pressures initially rose above baseline levels and later returned to normal. We conclude that a length-tension relation is present in the preinnervated embryonic heart and that vascular resistance changes inversely with loading conditions. We speculate that these mechanisms are the primary hemodynamic control mechanism in the early chick embryo.
Circus movement atrial flutter in the canine sterile pericarditis model. Activation patterns during initiation, termination, and sustained reentry in vivo.
Authors: Schoels W , Gough W B , Restivo M , el-Sherif N
Published: June 2012

The mechanisms of single-loop reentry in a syncytium without anatomically predetermined pathways have not been shown. Using a "jacket electrode" with 111 bipolar electrodes in a nylon matrix, we mapped in situ the atrial epicardial surface during atrial flutter in dogs with sterile pericarditis. Of 21 episodes of reentrant atrial flutter, only four showed double-loop ("figure-eight") reentry, whereas in 17 episodes a single loop was present. During initiation of single-loop reentry, an arc of functional block extended to the atrioventricular (AV) ring. This forced activation to proceed as a single wave around the free end of the arc, before breaking through the arc close to the AV ring. Activation continued as one loop around an arc close to the AV ring (in eight episodes) or around a combined functional and anatomic obstacle (in nine episodes) when the arc joined an atrial vessel. A zone of slow conduction was consistently bordered by the arc of block and the AV ring or by the anatomic obstacle and the AV ring. Spontaneous termination occurred when conduction failed in this area and the arc rejoined the AV ring. High-density recordings (2 mm) along the arc of block showed double potentials separated by an isoelectric interval, interpreted as local activation and electrotonus due to activation on the opposite side of the arc. Histologically, a diffuse inflammatory reaction involved 50-80% of the atrial wall. A transitional layer of myocardial bundles with preserved cross striation, but separated by edema and inflammatory cells, was enclosed between an epicardial layer of fragmented myocytes and an endocardial layer of grossly intact myocardium. There were no distinctive features at sites of functional conduction block or slowed conduction. In conclusion, single-loop reentry is the common pattern during atrial flutter in this model. Its induction depends on an interaction of the AV ring, a functional arc of block, and a zone of slow conduction. The location of the inferior vena cava predisposes the lower right atrium to this type of reentry.
H(+)-induced vasodilation of rat aorta is mediated by alterations in intracellular calcium sequestration.
Authors: Loutzenhiser R , Matsumoto Y , Okawa W , Epstein M
Published: June 2012

Acidosis induces vasodilation both in vivo and in vitro. Although it is commonly surmised that acidosis alters contractility by affecting contractile proteins and calcium entry, the exact role of these mechanisms in acidosis-induced vasodilation has not been determined. In the present study, we demonstrated that a novel mechanism, involving increased calcium sequestration into intracellular sites sensitive to norepinephrine, mediates the vasodilation associated with relatively modest decreases in pH. The effects of changing pH from 7.4 to 7.0 on tension development, 45Ca fluxes, and the norepinephrine-releasable intracellular calcium stores were studied in isolated rat aorta. Acute acidification produced marked endothelium-independent dilations of aortic rings that had been precontracted with norepinephrine. In contrast, this maneuver had only modest effects on contractions elicited by 80 mM KCl or phorbol ester. Acidification in this range did not alter basal or norepinephrine-stimulated undirectional 45Ca influx, nor did it reduce the norepinephrine-induced net gain in 45Ca content. Furthermore, neither norepinephrine-stimulated 45Ca efflux nor the peak contractile response to norepinephrine in calcium-free buffer was affected, although in this setting, the duration of the phasic contractile response was shortened. When calcium was restored to tissues exposed to norepinephrine in calcium-free buffer, acidification slowed the rate of tension development without altering 45Ca uptake, thus changing the relation between tension development and calcium entry. These effects of acidification were shown to be associated with an increase in the amount of calcium sequestered into the norepinephrine-sensitive intracellular calcium store. These findings clearly indicate that acidification, within a range that has no effect on other aspects of smooth muscle activation, elicits vasodilation by stimulating intracellular calcium sequestration. This action may represent a predominant mechanism whereby acidosis alters vascular smooth muscle contractility.
Inotropic and calcium kinetic effects of calcium channel agonist and antagonist in isolated cardiac myocytes from cardiomyopathic hamsters.
Authors: Sen L Y , O'Neill M , Marsh J D , Smith T W
Published: June 2012

The mechanism by which heart cells of cardiomyopathic (CM) hamsters become calcium overloaded is not known. We examined the number of slow calcium channels, calcium uptake via slow calcium channels, calcium pool sizes, and the contractile response to Bay K 8644, verapamil, and nifedipine using isolated cardiac myocytes from 8-9-month-old CM hamsters (BIO 14.6) and age-matched normal controls. The number of dihydropyridine binding sites as assessed by specific binding of [3H]PN200-110 was similar in the two groups (control hearts: Bmax = 333 +/- 89 [mean +/- SD] fmol/mg; CM hearts: Bmax = 357 +/- 75 fmol/mg; n = 5 experiments, p = 0.6). Current density through L-type calcium channels was determined using the whole-cell clamp technique (at -50 mV holding potential and -10 mV test potential) and was the same in CM myocytes (17.8 +/- 1.5 [mean +/- SD] pA/pF) and control myocytes (18.6 +/- 2.1 pA/pF) (n = 5 experiments, p = 0.5). The current-voltage relation (test potentials varied from -40 to +50 mV) was also the same in CM and control cells, as was apparent threshold, peak current, and reversal potential. However, the initial rate of 45Ca influx as well as the size of the rapidly exchangeable calcium pool was significantly greater in myocytes obtained from CM than from normal hamsters. In both myocyte preparations, Bay K 8644 increased the rate of 45Ca uptake by 25% at 60 seconds; verapamil decreased 45Ca uptake at 60 seconds by 16% and 17% in normal and CM hamsters, respectively. A similar inhibitory effect was observed with nifedipine. The amplitude of cell motion in cells driven at 1.5 Hz as assessed by an optical-video system increased progressively with increasing concentrations of extracellular calcium or Bay K 8644 in cardiac myocytes from normal or CM hamsters. However, the concentration-effect curves for the two effectors were shifted to the left in CM cells compared with cells from normal hamsters. Both preparations demonstrated similar contractile responses to verapamil and nifedipine. These findings demonstrate that single enzymatically dissociated cardiac myocytes from CM hamsters have impaired contractile properties analogous to those seen in the intact heart and thus provide a useful experimental system in which to study underlying cellular mechanisms operative in this model of heart failure. Our results further indicate that calcium overload in CM hamster cardiac myocytes may not be due to increased calcium influx via dihydropyridine-sensitive calcium channels, as suggested previously, but rather to abnormalities of intracellular calcium homeostasis.
Evidence against the "early protection-delayed death" hypothesis of superoxide dismutase therapy in experimental myocardial infarction. Polyethylene glycol-superoxide dismutase plus catalase does not limit myocardial infarct size in dogs.
Authors: Tanaka M , Stoler R C , FitzHarris G P , Jennings R B , Reimer K A
Published: June 2012

We previously found that superoxide dismutase (SOD) did not limit myocardial infarct size after 40 or 90 minutes of ischemia and 4 days of reperfusion in dogs. Because some other studies have shown limitation of infarct size after shorter periods of reperfusion, we postulated that our negative results might be due to late reperfusion injury mediated by superoxide anions produced after excretion of SOD. To test this "early protection-delayed death" hypothesis, we have examined whether SOD, conjugated to polyethylene glycol (PEG-SOD) to prolong its circulating half-life, limited myocardial infarct size. The circumflex artery was occluded for 90 minutes followed by 4 days of reperfusion. PEG-SOD (total dose, 10,000 units/kg) and catalase (55,000 units/kg) were given during the 30 minutes before reperfusion. Plasma SOD levels in the treated group were 330 +/- 20 units/ml at the onset of reperfusion and 140 +/- 10 units/ml on day 4 (circulating half-life, 75 +/- 5 hours) versus 5 +/- 1 units/ml in controls. Histological infarct size was 37.1 +/- 4.2% of the area at risk in the treated group (n = 11) versus 44.5 +/- 6.2% in controls (n = 10) (p = NS). Infarct size and collateral blood flow were inversely related in controls; PEG-SOD and catalase did not shift this regression (p = NS by analysis of covariance). Thus, infarct size was not limited when measured after 4 days of reperfusion, even though plasma SOD exceeded 100 units/ml throughout this reperfusion period.(ABSTRACT TRUNCATED AT 250 WORDS)
Cloning and characterization of a vertebrate cellular myosin regulatory light chain complementary DNA.
Authors: Zavodny P J , Petro M E , Lonial H K , Dailey S H , Narula S K , Leibowitz P J , Kumar C C
Published: June 2012

We have isolated two series of complementary DNAs (cDNAs) from a chicken gizzard cDNA library encoding two isoforms of phosphorylatable myosin regulatory light chain (RLC). One of the cDNAs encodes a previously isolated smooth muscle myosin RLC (also referred to as LC20-A); the other encodes a protein that shares 92% homology with the LC20-A isoform. The phosphorylatable threonine and serine residues at positions 18 and 19 of the two myosin RLC sequences are conserved. The two cDNAs are 81% homologous at the nucleotide level over the coding region; the 5' and 3' untranslated regions are divergent. Most of the DNA nonhomology in the coding region does not affect the protein sequence, indicating strong evolutionary conservation pressure to maintain the myosin RLC structure. Northern blot analysis using 3' untranslated region probes reveals restrictive tissue specific expression of one myosin RLC isoform (LC20-A) in smooth muscle tissue and not in other tissues examined. In contrast, the novel myosin RLC isoform messenger RNA (mRNA) is uniformly expressed in all smooth and nonmuscle tissues examined and is designated as cellular myosin RLC for this reason. Our results indicate that cellular and smooth muscle myosin RLC isoforms are distinct and are encoded by separate genes. This report describes the cloning of a novel vertebrate cellular myosin RLC mRNA that differs from previously characterized smooth muscle RLC isoform mRNAs in both primary sequence and expression pattern.
Synergistic inhibition of platelet aggregation by fibrinogen-related peptides.
Authors: Adelman B , Gennings C , Strony J , Hanners E
Published: June 2012

We have evaluated the ability of the fibrinogen-related peptides Gly-Arg-Gly-Asp-Ser (GRGDS), Gly-Gln-Gln-His-His-Leu-Gly-Gly-Ala-Lys-Gln-Ala-Gly-Asp-Val (gamma-chain peptide), and Gly-Pro-Arg-Pro (GPRP) to inhibit platelet aggregation in platelet-rich plasma individually and in combination. When used alone, GRGDS totally inhibited ADP-induced aggregation of human platelets in platelet-rich plasma; however, the maximum inhibitory effect of the other peptides was less than 80%. The concentrations necessary to inhibit platelet aggregation in plasma by 50% were 100 mumols/l and 1 and 3.2 mmol/l for GRGDS, gamma-chain peptide, and GPRP, respectively. When evaluating the effect of peptide mixtures, we discovered that the combination GPRP + GRGDS worked together synergistically (p less than 0.001, analysis by surface response methodology), whereas GPRP + gamma-chain peptide did not. For example, our analysis indicated that a mixture of 50 mumols/l GRGDS plus 180 mumols/l GPRP would produce 50% inhibition of platelet aggregation. This is an effect twofold greater than that produced by 50 mumols/l GRGDS alone, and one that would require an 18-fold greater concentration of GPRP if used alone. These data indicate that the combination GPRP + GRGDS inhibited platelet aggregation in plasma in a synergistic fashion and suggest the potential value of their combined use in antithrombotic therapy.
Mechanism of adenosine-induced inhibition of calcium current in guinea pig ventricular cells.
Authors: Kato M , Yamaguchi H , Ochi R
Published: June 2012

The mechanism of adenosine-induced inhibition of Ca2+ currents was studied by recording single-channel Ca2+ currents from cell-attached patches on isolated guinea pig ventricular cells with pipettes containing 50 or 100 mM Ba2+. Numerous 100-msec depolarization steps were applied repetitively at 2 Hz from the resting potential of approximately -70 mV. The addition of 0.1 mM adenosine to the superfusate in the presence of 100 nM isoproterenol depressed the isoproterenol-induced increase in ensemble-averaged current: in peak amplitude, from 258 +/- 105% (mean +/- SD) (p less than 0.01) that of control in the presence of isoproterenol to 153 +/- 41% (n = 7) (p less than 0.05) by the addition of adenosine. In these patches, adenosine did not much affect the open probability in nonblank sweeps (control, 0.10 +/- 0.05; isoproterenol, 0.11 +/- 0.08; adenosine and isoproterenol, 0.08 +/- 0.05), but significantly decreased channel availability, defined as the rate of current-containing sweeps in total sweeps (control, 0.36 +/- 0.17; isoproterenol, 0.69 +/- 0.16 [p less than 0.01]; adenosine and isoproterenol, 0.45 +/- 0.20 [p less than 0.01]). The decrease of channel availability by adenosine was due to the shortening of the duration of the available state and the prolongation of that of the unavailable state. The depressive action of adenosine was suppressed by 0.1 mM theophylline. The single-channel conductance in the presence of 100 mM Ba2+ and Bay K 8644 was 26 pS and was not affected by isoproterenol or adenosine. We conclude that adenosine decreases Ca2+ current under beta-adrenergic stimulation mainly by reducing channel availability.
Neuropeptide Y modulates vasoconstriction in coronary microvessels in the beating canine heart.
Authors: Komaru T , Ashikawa K , Kanatsuka H , Sekiguchi N , Suzuki T , Takishima T
Published: June 2012

The purpose of this study was to determine whether neuropeptide Y has a direct vasoconstrictor effect at low doses, mimicking the physiological plasma concentration on the specific site(s) of coronary arterial microvessels in in situ beating canine left ventricles. Coronary microvessels were directly observed by means of an intravital microscope and video system equipped with a floating objective. Epi-illuminated fluorescence coronary microangiography was performed in open-chest anesthetized dogs (n = 14) to examine the changes in internal diameter of epimyocardial arterial microvessels. Flow velocity of fluorescently labeled microshperes in capillaries was also measured (n = 6). To eliminate secondary effects of neuropeptide Y on coronary microvessels via autonomic nervous modulation, experiments were conducted under pharmacological blockade of the regional autonomic nervous system by intracoronary injection of propranolol, 50 micrograms/kg; phentolamine, 100 micrograms/kg; and atropine, 5 micrograms/kg. Aortic pressure and heart rate were kept constant during the experiments. Intracoronary infusion of three different doses of neuropeptide Y (1, 10, and 100 pmol/kg/min) for 5 minutes significantly constricted small microvessels (less than 100 microns in diameter) (-5.2 +/- 1.4%, -8.5 +/- 1.5%, and -14.0 +/- 1.7%; p less than 0.05 versus before neuropeptide Y at each dose), medium microvessels (100-200 microns in diameter) (-5.5 +/- 1.6%, -10.6 +/- 1.8%, and -16.8 +/- 2.1%, p less than 0.05 versus before neuropeptide Y at each dose), and large microvessels (greater than 200 microns in diameter) (-3.6 +/- 0.6%, -5.8 +/- 0.8%, and -10.0 +/- 1.1%; p less than 0.05 versus before neuropeptide Y at each dose) in a dose-dependent manner. Capillary flow velocity was reduced by 17.2 +/- 3.1% by an intracoronary dose of 100 pmol/kg/min of neuropeptide Y (p less than 0.05). The present study indicates that low doses of neuropeptide Y exert a homogeneous direct vasoconstrictor effect on various sizes of coronary arterial microvessels and reduce capillary flow velocity. These results suggest that neuropeptide Y may play a physiological role in modulating coronary microvascular tone.
Enhanced alpha 1-adrenergic responsiveness in cardiomyopathic hamster cardiac myocytes. Relation to the expression of pertussis toxin-sensitive G protein and alpha 1-adrenergic receptors.
Authors: Sen L , Liang B T , Colucci W S , Smith T W
Published: June 2012

The pathogenesis of the myopathy occurring in the heart of the cardiomyopathic strain of the Syrian hamster is not well understood but is believed to be associated with abnormal calcium handling by myopathic cells. The purpose of this study was to determine whether the cardiomyopathy occurring in strain BIO 14.6 animals is associated with an enhanced alpha 1-adrenergic receptor-mediated rise in cytosolic calcium, whether a pertussis toxin-sensitive G protein is involved in coupling the alpha 1-adrenergic receptor to changes in intracellular calcium and whether enhanced alpha 1 responsiveness is associated with an increase in the level of expression of the alpha 1-adrenergic receptor or in the pertussis toxin-sensitive G protein or proteins. To test the hypothesis that the cardiomyopathic state is associated with a greater alpha 1-receptor-mediated rise in cytosolic calcium, we studied the effect of phenylephrine (in the presence of propranolol) on time-averaged cytosolic calcium concentration ([Ca2+]i) in isolated cardiac myocytes from cardiomyopathic and age-matched control hamsters. Phenylephrine caused a greater increase both in time-averaged [Ca2+]i (an increase of 48 +/- 8% versus 12 +/- 3%, p less than 0.01) and in contractility (+181 +/- 22% versus +35 +/- 9%, p less than 0.01) in cardiomyopathic than in normal cardiac myocytes. Exposure to pertussis toxin (200 ng/ml for 3 hours) attenuated the alpha 1-adrenergic receptor-mediated increase in contractility and time-averaged [Ca2+]i in both cardiomyopathic and normal cells. The level of pertussis toxin-sensitive G protein, as determined by pertussis toxin-mediated [32P]ADP-ribosylation, was 1.6-fold higher in cardiomyopathic versus normal hamster hearts. The density of alpha 1-adrenergic receptors, as measured by the antagonist radioligand [3H]prazosin and the affinity of the receptor for agonist and antagonist were similar in myopathic and normal heart membranes. Thus, in cardiac myocytes from hamsters, the alpha 1-adrenergic receptor-mediated effects on [Ca2+]i and contractility appear to be mediated by a pertussis toxin-sensitive G protein or proteins. In myocytes from cardiomyopathic hamsters, these alpha 1-adrenergic effects were increased in magnitude, as was the level of pertussis toxin-sensitive G protein, but there was no measurable alteration in the density or ligand binding properties of alpha 1-adrenergic receptors.
Studies of recombinant plasminogen activator inhibitor-1 in rabbits. Pharmacokinetics and evidence for reactivation of latent plasminogen activator inhibitor-1 in vivo.
Authors: Vaughan D E , Declerck P J , Van Houtte E , De Mol M , Collen D
Published: June 2012

The pharmacokinetics of human recombinant plasminogen activator inhibitor-1 (rPAI-1) was studied in rabbits. Latent rPAI-1 (0-2 units of tissue-type plasminogen activator neutralizing activity per microgram protein); reactivated rPAI-1 (approximately 150 units/micrograms); and chloramine T-oxidized, nonreactivatable rPAI-1 (approximately 0.7 units/microgram) were studied. The pharmacokinetic parameters for the disposition of rPAI-1 antigen after an intravenous bolus injection of 1.0 or 2.5 mg/kg rPAI-1 were very similar for all three forms: the initial volume of distribution was approximately 60 ml/kg, the initial half-life in plasma was 6 minutes, and the plasma clearance was approximately 4 ml/kg/min. The disposition of PAI activity after injection of reactivated rPAI-1 was similar to that of rPAI-1 antigen. Injection of latent rPAI-1 was associated with a nearly threefold increase in the specific activity of circulating PAI-1 from 2 units/micrograms to 5.0 +/- 1.1 units/micrograms (p less than 0.01) within 1 minute, followed by a cumulative 25-fold increase in specific activity over 1 hour (p = 0.01). In contrast, the specific activity of oxidized or reactivated preparations of rPAI-1 did not increase in the first several minutes after injection. These findings support the existence of a fast-acting but low-capacity mechanism for the reactivation of rPAI-1 in vivo.
Remodeling of the rat right and left ventricles in experimental hypertension.
Authors: Brilla C G , Pick R , Tan L B , Janicki J S , Weber K T
Published: June 2012

Pathological left ventricular hypertrophy in renovascular hypertension is associated with the accumulation of fibrillar collagen within the extracellular space and around intramyocardial coronary arteries. Even though the angiotensin converting enzyme inhibitor captopril was previously found to attenuate this interstitial and perivascular fibrosis, the relative importance of arterial and ventricular systolic pressures versus circulating angiotensin II (AII) and aldosterone (AL) in promoting hypertrophy and collagen accumulation in renovascular hypertension is uncertain. By drawing on the in-parallel arrangement of the right and left ventricles, with respect to their coronary circulation, and the in-series mechanical alignment of the ventricles, with a pressure-overloaded left and a normotensive right ventricle, this study sought to address this uncertainty. Three models of experimental hypertension, each having a different circulating AII and AL profile, were examined and compared with their controls: renovascular hypertension, where both AII and AL are increased; infrarenal aorta banding, where AII and AL are normal; and a chronic infusion of AL, where AII is suppressed or normal and AL is increased. In renovascular hypertension, as well as with AL, we found a significant rise in the interstitial collagen volume fraction and perivascular collagen area of the pressure-overloaded, hypertrophied left ventricle as well as the normotensive, nonhypertrophied right ventricle. This remodeling was not seen in either ventricle with infrarenal aorta banding despite comparable systemic hypertension and left ventricular hypertrophy. Thus, in experimental arterial hypertension in the rat, myocyte and nonmyocyte compartments of the myocardium are under separate controls: myocyte hypertrophy is most closely related to ventricular loading while circulating AII and AL, acting alone or in concert with other humoral factors, regulate the accumulation of collagen within the right and left ventricles.
Action potential propagation in a thick strand of cardiac muscle.
Authors: Roth B J
Published: June 2012

A theoretical model of action potential propagation in a thick strand of cardiac muscle is presented. The calculation takes into account the anisotropic and syncytial properties of the tissue, the presence of the interstitial space, the effect of the surrounding tissue bath, and the variation of the potential both along the strand length and across the strand cross section. The bidomain model is used to represent the electrical properties of the tissue, and the Ebihara-Johnson model is used to represent the properties of the active sodium channels. The calculated wave front is curved, with the action potential at the surface of the strand leading that at the center. The rate of rise of the action potential and the time constant of the action potential foot vary with depth into the tissue. The velocity of the wave front is nearly independent of strand radius for radii greater than 0.5 mm. The conduction velocity decreases as the volume fraction of the interstitial space decreases. In the limit of tightly packed cells, an action potential propagates quickly over the surface of the strand; the bulk of the tissue is then excited by a slow inward wave front initiated on the surface. This model does not predict an increase in conduction velocity when cells are tightly packed, a hypothesis that has been proposed previously to explain the fast conduction velocity in Purkinje fibers of some species.
Pericardial influences on right and left ventricular filling dynamics.
Authors: Hoit B D , Dalton N , Bhargava V , Shabetai R
Published: June 2012

The influence of the pericardium on right and left ventricular filling was studied using two-dimensional and Doppler echocardiography in 14 open-chest dogs. Doppler echo parameters of filling included early (E) and late (A) velocities and their ratio (E/A) for the mitral and tricuspid valves. Right and left ventricular volumes were calculated from orthogonal two-dimensional echocardiographic images. Data were compared at three levels of left ventricular end-diastolic pressure (6 +/- 2, 13 +/- 3, and 21 +/- 4 mm Hg) at matched heart rates before and after pericardiectomy. The instantaneous diastolic pressure gradient was measured in 12 of the dogs. Pericardiectomy resulted in an increase in early mitral velocity, peak early diastolic pressure gradient, and E/A but not early mitral velocity normalized for end-diastolic volume. In contrast, for the tricuspid valve flow, pericardiectomy did not change E but caused a marked increase in A and a decrease in E/A. Right ventricular end-diastolic volumes at matched left ventricular end-diastolic volumes were similar before and after the pericardium was removed. However, removal of the pericardium caused a significant decrease of the slope for the right (86.0 +/- 27.0 x 10(-4) versus 50.0 +/- 19.5 x 10(-4) mm Hg/ml, p less than 0.01), but not left, ventricular ln end-diastolic pressure-volume relation (21.2 +/- 9.2 x 10(-3) versus 21.4 +/- 5.3 x 10(-3) mm Hg/ml, p = NS), and a decrease of the pressure intercept for the left (3.0 +/- 2.0 versus 1.6 +/- 0.9 mm Hg, p less than 0.05), but not right, ventricular ln end-diastolic pressure-volume relation (2.8 +/- 1.4 versus 1.4 +/- 0.8 mm Hg, p = NS). In conclusion, filling of the two ventricles is affected by the pericardium over a wide range of physiological ventricular volumes and pressures. At matched left ventricular end-diastolic volume, pericardiectomy causes a fundamental alteration in right, but not left, ventricular filling.
Effect of a pressor infusion of angiotensin II on sympathetic activity and heart rate in normal humans.
Authors: Goldsmith S R , Hasking G J
Published: June 2012

We tested the hypothesis that pressor infusions of angiotensin II (AII) could stimulate the sympathetic nervous system as reflected by norepinephrine (NE) spillover in humans. AII was infused at 5 ng/kg/min in six healthy volunteers, with vehicle and phenylephrine infusions as controls, on 3 separate days. Heart rate, mean arterial pressure, plasma NE, NE clearance, and NE spillover were assessed before and after 30-minute infusions of AII, vehicle, or phenylephrine in the supine position and then after 15 minutes of head-up and 15 minutes of head-down tilt. Both AII and phenylephrine raised mean arterial pressure (88 +/- 9.6 to 103 +/- 14 mm Hg, p less than 0.001, and 91 +/- 7.6 to 104 +/- 9.2 mm Hg, p less than 0.001, respectively), whereas heart rate fell only with phenylephrine (60 +/- 6 to 51 +/- 6.3 beats/min, p less than 0.001). Neither plasma NE nor NE spillover was affected by either infusion, and NE clearance declined slightly with both. No changes occurred in any variable during vehicle infusions in the supine position. During upright tilt, NE spillover increases were attenuated by both AII and phenylephrine while NE clearance changes were slightly greater, leaving plasma NE increases similar on each day. During head-down tilt, NE and NE spillover declined comparably on each study day.(ABSTRACT TRUNCATED AT 250 WORDS)