bluuebunny/crossref_metadata_2025 huggingface dataset:
Endothelin and increased contractility in adult rat ventricular myocytes. Role of intracellular alkalosis induced by activation of the protein kinase C-dependent Na(+)-H+ exchanger.
Authors: Krämer B K , Smith T W , Kelly R A
Published: June 2012

Endothelin, a 21-amino acid vasoactive peptide, is among the most potent positively inotropic agents yet described in mammalian heart. Having demonstrated that endothelin's inotropic effect is due, in part, to an apparent sensitization of cardiac myofilaments to intracellular calcium, we determined whether this could be due to a rise in intracellular pH (pHi). In isolated adult rat ventricular cells loaded with the H(+)-selective fluorescent probe BCECF, 100 pM endothelin increased contractile amplitude to 190 +/- 26% of baseline and pHi by 0.08 +/- 0.02 (n = 8), whereas 1 nM endothelin increased pHi by 0.13 +/- 0.03 with little further increase in contractility. Amiloride (10(-4)M) prevented the increase in pHi in response to endothelin and reduced the inotropic response by 45%, although the inotropic effect could be readily restored by subsequent NH4Cl-induced alkalinization. Similarly, inhibitors of protein kinase C (H-7 and sphingosine) diminished or abolished the rise in pHi after endothelin superfusion while causing a decline in its inotropic effect comparable with that observed with amiloride. Pretreatment with pertussis toxin, which we have demonstrated results in complete ADP-ribosylation of the alpha-subunits of Go and Gi GTP-binding proteins and abolition of endothelin's positive inotropic effect, only partially reduced the intracellular alkalinization induced by the peptide, suggesting a complex signal transduction mechanism. Thus, the positive inotropic action of endothelin is due in part to stimulation of the sarcolemmal Na(+)-H+ exchanger by a protein kinase C-mediated pathway, resulting in a rise in pHi and sensitization of cardiac myofilaments to intracellular Ca2+.
Delayed end ejection increases isovolumic ventricular relaxation rate in isolated perfused canine hearts.
Authors: Hori M , Kitakaze M , Ishida Y , Fukunami M , Kitabatake A , Inoue M , Kamada T , Yue D T
Published: June 2012

We sought to determine the ejection variables that are principally responsible for increases in isovolumic ventricular relaxation rate observed with increases in stroke volume. In nine isolated canine hearts, left ventricular ejection was controlled by patterns specially designed to isolate the ejection parameters most critical to isovolumic relaxation rate. When stroke volume was augmented by increases in end-diastolic volume (EDV) with end-systolic volume (ESV) held constant, isovolumic ventricular relaxation rate was unchanged, as gauged by the time constants of single-exponential fits to decaying pressure. In contrast, when ESV was decreased with EDV held constant, isovolumic relaxation time constants decreased significantly, from approximately 100 to 70 msec (protocol I). The important difference in these two situations might have been that the time of end ejection was delayed in the case with faster isovolumic relaxation. To rule out other parameters that may have influenced isovolumic relaxation, ejection velocity was varied in another protocol (protocol II) by either delays in time of the onset of ejection or advances in end-ejection time, always with constant ESV and EDV. Here isovolumic relaxation was progressively slowed as end ejection occurred earlier, whereas isovolumic relaxation rate was insensitive to changes in the onset of ejection, consistent with the unique importance of end ejection to isovolumic relaxation. In fact, our analysis reveals the remarkable finding that changes in isovolumic relaxation time constant produced by either protocol I or protocol II could be related quantitatively to end ejection by a single curve.(ABSTRACT TRUNCATED AT 250 WORDS)
Disparate effects of colchicine on thyroxine-induced cardiac hypertrophy and adrenoceptor changes.
Authors: Limas C , Limas C J
Published: June 2012

Short-term (5 days) administration of L-thyroxine (0.1 mg/kg i.p. daily) to adult Sprague-Dawley rats induces a modest degree of cardiac hypertrophy (22% increase in heart weight/body weight ratios) and directionally opposite changes in cardiac adrenoceptors (24% increase in beta-adrenoceptors and 20% decline in alpha 1-adrenoceptors). Pretreatment with colchicine did not affect the ability of L-thyroxine to induce cardiac hypertrophy but prevented its effects on both beta- and alpha 1-adrenoceptors. These results suggest a selective involvement of microtubules in the action of thyroid hormones on the expression of cardiac adrenoceptor genes.
Lack of effect of isoproterenol on unloaded velocity of sarcomere shortening in rat cardiac trabeculae.
Authors: de Tombe P P , ter Keurs H E
Published: June 2012

Several recent reports have indicated that catecholamines may act directly on the crossbridge cycle, independent of intracellular calcium concentration changes. The present study investigated the effect of isoproterenol on peak force during twitches at constant sarcomere length and unloaded velocity of sarcomere shortening in isolated right ventricular trabeculae of hearts with V1 or V3 isomyosin obtained from euthyroid and hypothyroid rats, respectively. Hypothyroidism was induced by treatment of the rats with propylthiouracil for 6 weeks. Electrophoretic analysis showed that the hearts of hypothyroid animals were composed only of V3 isomyosin, whereas the hearts of euthyroid animals were composed predominantly of V1 isomyosin. Force development was measured with a silicon strain gauge and sarcomere length with laser diffraction techniques; the shortening velocity was determined from contractions in which sarcomere length was initially held constant followed by a quick release to zero load and a controlled release at zero load. Both isometric twitch force and unloaded sarcomere shortening velocity were sigmoidal functions of [Ca2+]o and of the concentration of isoproterenol. At optimal [Ca2+]o, unloaded shortening velocity was 40% lower in myocardium of hypothyroid animals than in myocardium of euthyroid animals. Isoproterenol increased the sensitivity of isometric twitch force and unloaded shortening velocity to [Ca2+]o in trabeculae from both euthyroid and hypothyroid animals. Isoproterenol did not increase unloaded shortening velocity at optimal [Ca2+]o, regardless of the thyroid state. From these results we conclude that beta-adrenergic stimulation per se does not accelerate the rate limiting step in the crossbridge cycle that determines unloaded sarcomere shortening velocity in the intact cardiac cell.
Conditioning prepulse of biphasic defibrillator waveforms enhances refractoriness to fibrillation wavefronts.
Authors: Swartz J F , Jones J L , Jones R E , Fletcher R
Published: June 2012

The mechanism of biphasic waveform defibrillation threshold reduction is unknown. We tested the hypothesis that, during refractory period stimulation, sarcolemmal hyperpolarization by the first pulse of biphasic waveforms facilitates excitation channel recovery, which enhances graded responses produced by the second depolarizing pulse. This prolongs cellular refractoriness to fibrillation wavefronts when compared with a monophasic depolarizing stimulus. Monophasic (10 msec, rectangular wave) or symmetrical biphasic (10 msec, each pulse) current injection S2 stimuli at 1.5 and two times S1 threshold were used to scan the S1 action potential refractory period (S1 cycle length, 600 msec) in myocardial cell aggregates. S2 waveforms were delivered with normal and reversed polarity to test the hyperpolarizing action of biphasic waveforms. Responses to an S3 stimulus, which simulated a potential incoming fibrillation wavefront, were also determined. Results showed that biphasic S2 waveforms produced longer graded responses during and immediately after the S1 refractory period than did corresponding monophasic S2 waveforms. The maximum difference in response duration produced by the biphasic and monophasic waveforms was 58.6 +/- 10.0 msec (p less than 0.001). This maximum difference occurred 10 msec before the end of the S1 refractory period. The longer response durations produced by biphasic S2 also produced longer refractoriness to the S3 stimulus. The maximum difference in total refractoriness to S3 of 51.8 +/- 2.8 msec (p less than 0.002) occurred at the same S1S2 coupling interval as the maximum difference in S2 response duration. Prolonged refractoriness may protect ventricular cells from refibrillation wavefronts and act as the cellular basis for greater biphasic waveform defibrillation efficacy.
Effect of coronary hyperemia on Emax and oxygen consumption in blood-perfused rabbit hearts. Energetic consequences of Gregg's phenomenon.
Authors: Goto Y , Slinker B K , LeWinter M M
Published: June 2012

To assess the relation between increases in contractile function and oxygen consumption (VO2) during increased coronary flow (Gregg's phenomenon), we measured the end-systolic pressure-volume relation and the relation between VO2 and left ventricular systolic pressure-volume area (PVA, a measure of total mechanical energy output) in blood-perfused, isovolumically contracting rabbit hearts during control and intracoronary adenosine infusion. During adenosine infusion at a constant perfusion pressure (93 +/- 11 mm Hg), coronary flow increased by 99 +/- 76% (p less than 0.01), and the slope of the end-systolic pressure-volume relation, Emax (ventricular contractility index), increased by 18 +/- 15% (p less than 0.01). When compared at the same left ventricular volume, PVA increased by 20 +/- 14% (p less than 0.01) and VO2 by 19 +/- 15% (p less than 0.01) with adenosine. The VO2-PVA relation was linear under each condition (both median r = 0.98). With increased coronary flow, the VO2-intercept of the VO2-PVA relation (unloaded VO2) increased by 22 +/- 18% (p less than 0.01) without a change in the slope; that is, a parallel upward shift was observed, indicating that the contractile efficiency (energy conversion efficiency of the contractile machinery) remained constant. These increases in Emax and unloaded VO2 were not eliminated by beta-adrenergic blockade with propranolol. We conclude that increased coronary flow with adenosine at a constant perfusion pressure augments both Emax and the nonmechanical energetic cost for excitation-contraction coupling and basal metabolism via nonadrenergic mechanisms, without changing contractile efficiency.
Human leukoagglutinating antibody evokes cooperative leukotriene synthesis in pulmonary microvasculature. Model of transfusion-related acute lung injury.
Authors: Grimminger F , Kreusler B , Schneider U , von Witzleben E , Walmrath D , Neppert J , Seeger W
Published: June 2012

Leukoagglutinating antibodies have been implicated in the development of transfusion-related acute lung injury. In the present study, human neutrophil leukotriene generation was provoked by an anti-5b immunoglobulin G, isolated from a multiparous donor plasma that caused noncardiogenic lung edema during transfusion therapy. In 5b-positive polymorphonuclear neutrophils (PMNs), the antibody stimulated marked arachidonic acid metabolism, dependent on the presence of plasma as the complement source. Quantity and profile of lipid mediators (leukotriene B4 and its omega-oxidation products, 5-hydroxyeicosatetraenoic acid, and nonenzymatic hydrolysis products of leukotriene A4) corresponded to those repeatedly described after PMN in vitro stimulation with the artificial calcium ionophore A23187. Anti-5b challenge of PMNs sequestered in the microvasculature of perfused rabbit lungs did, however, induce a markedly modified metabolite profile. Nonenzymatic hydrolysis products of leukotriene A4 were not detected, and 5-hydroxyeicosatetraenoic acid was markedly reduced. In contrast, cysteinyl leukotrienes were measured as predominant compounds, with rapid appearance of leukotriene C4 and more protracted generation of leukotriene E4. Leukotriene B4 and its omega-oxidation products were released with similar kinetics, but in lower amounts, as compared with the isolated PMN stimulation. Anti-5b challenge of PMNs coincubated with pulmonary artery endothelial cells in vitro, but not stimulation of either cell type alone, provoked marked generation of cysteinyl leukotrienes. These findings suggest modulation of PMN 5-lipoxygenase metabolism in favor of leukotriene A4 transfer to adjacent acceptor cells with subsequent enzymatic conversion to cysteinyl leukotrienes under conditions of lung vascular sequestration. Endothelial cells appear to serve as predominant cooperative cells under circumstances of blood-free lung perfusion. PMN-related transcellular eicosanoid synthesis may be involved in the pathogenesis of transfusion-evoked acute lung injury.
Changes in diastolic cardiac function in developing and stable perinephritic hypertension in conscious dogs.
Authors: Gelpi R J , Pasipoularides A , Lader A S , Patrick T A , Chase N , Hittinger L , Shannon R P , Bishop S P , Vatner S F
Published: June 2012

The effects of developing perinephritic hypertension (2-3 weeks) and a more stable period of perinephritic hypertension (approximately 14 weeks) were examined on indexes of left ventricular (LV) diastolic function in conscious, chronically instrumented dogs. The complete period of diastole was studied using indexes of isovolumic relaxation (tau), early filling (LV +dD/dt), and stiffness (myocardial stiffness and chamber stress/diameter ratio). During developing hypertension, increased LV end-diastolic pressure, LV end-diastolic stress, peak filling rate, myocardial stiffness, and the stress/diameter ratio increased (p less than 0.05); the time constant tau was not changed. These changes were associated with preserved baseline levels of coronary blood flow (radioactive microspheres) but an impaired coronary vasodilator response to adenosine. Acute administration of phenylephrine in the normotensive dogs caused increases in systolic and diastolic stress and resulted in increases in myocardial stiffness and in the stress/diameter ratio similar to values observed in developing hypertension. During stable hypertension, LV end-diastolic stress, peak filling rate, and both parameters of late-diastolic function (myocardial stiffness and stress/diameter ratio) returned toward control values, but the isovolumic relaxation time constant was increased. Quantitative histological evaluation revealed no increase in stainable connective tissue in dogs with stable hypertension compared with control dogs, and hydroxyproline concentration was not increased in the subendomyocardium, midmyocardium, or subepimyocardium of the dogs with chronic perinephritic hypertension. Thus, in developing hypertension, major alterations in diastolic function were observed that were not structurally related, since these changes 1) could be induced in normal dogs by increasing preload and afterload acutely with phenylephrine and 2) were improved during the ensuing stable period of hypertension.
Sarcomere dynamics in cat cardiac trabeculae.
Authors: de Tombe P P , ter Keurs H E
Published: June 2012

The purpose of the present study was to describe sarcomere dynamics in thin trabeculae that were dissected from the right ventricle of kittens. The muscles were mounted in an experimental chamber and perfused with a modified Krebs-Henseleit solution (25 degrees C). Sarcomere length (SL) was measured by laser diffraction techniques; force, by a silicon strain gauge; and velocity of sarcomere shortening, by the "isovelocity release" technique. Contractile activation was varied by changing the calcium concentration in the bathing medium ([Ca2+]o). Slack SL was 1.85 +/- 0.04 microns. When length of the muscle was held constant, the sarcomeres in the central region of the muscle shortened during the twitch by up to 21%. Both peak sarcomere isometric twitch force and unloaded velocity of sarcomere shortening (Vo) were a sigmoidal function of [Ca2+]o. Maximum Vo was 9.8 +/- 0.2 microns/sec; maximum sarcomere isometric twitch force was 108 +/- 13.8 mN/mm2. The shape of the force-SL relation was a function of [Ca2+]o. At [Ca2+]o = 1.5 mM, the force-SL relation was curved with its convexity toward the abscissa; at [Ca2+]o = 6 mM, the relation was curved with its convexity toward the ordinate. Vo depended in a linear manner on SL up to 2.2 microns at [Ca2+]o = 1.5 mM. At [Ca2+]o = 6.0 mM, Vo depended also linearly on SL below 1.85 microns but became nearly independent of SL above 1.85 microns. Vo rose exponentially with time into the twitch up to 200 msec and remained constant thereafter at least up to 300 msec. Force, on the other hand, peaked at about 300 msec. These results are comparable with those found in rat myocardium, although cat myocardium is less sensitive to [Ca2+]o and twitch kinetics are significantly slower than those in rat myocardium.
Sex difference in presynaptic adrenergic inhibition of norepinephrine release during normoxia and ischemia in the rat heart.
Authors: Du X J , Dart A M , Riemersma R A , Oliver M F
Published: June 2012

Using a perfused innervated rat heart model, we studied the sex difference in the sympathetic nerve stimulation-induced norepinephrine release and its presynaptic alpha 2-adrenergic inhibition in normoxic and ischemic conditions. During normoxic perfusion, the alpha 2-adrenoceptor antagonist rauwolscine resulted in a higher overflow of norepinephrine during nerve stimulation in females than in males (p less than 0.05). This more marked potentiation of norepinephrine overflow in females was accompanied by an increased chronotropic and inotropic response (p less than 0.01). During early stop-flow ischemia neural norepinephrine overflow was lower in female than in male hearts (p less than 0.005). Rauwolscine enhanced norepinephrine overflow more in females than in males (p less than 0.05), thereby eliminating the initial difference in norepinephrine overflow during ischemia between the two sexes. Ovariectomy attenuated the presynaptic alpha 2-adrenergic inhibition of norepinephrine release compared with sham-operated females (p less than 0.02). No sex difference was found in either cardiac norepinephrine content or nonexocytotic norepinephrine overflow induced by a 40-minute period of stop-flow ischemia. Thus, presynaptic alpha 2-adrenergic inhibition of myocardial norepinephrine release is greater in female than in male rats. This difference persists into the early phase of ischemia and is largely responsible for the lower neural norepinephrine release in the female heart. Female hormones may increase presynaptic alpha 2-adrenergic activity in the heart.
Effect of sympathetic tone on pressure-diameter relation of rabbit mesenteric veins in situ.
Authors: Ozono K , Bosnjak Z J , Kampine J P
Published: June 2012

Although venous capacitance has been studied in the neurally isolated tissue or in the in vitro vein segment, this is the first study of sympathetic regulation of the pressure-diameter relation in mesenteric veins in situ, where innervation is kept intact. In 25 alpha-chloralose-anesthetized rabbits, mesenteric vein diameter (679 +/- 27 microns, ranges of 380-1,050 microns at initial state) and intravenous pressure were measured continuously at the same site by using videomicrometer and micropressure systems. Intravenous pressure was increased in a stepwise fashion from the baseline of 6-9 mm Hg to approximately 10, approximately 13, approximately 16, approximately 19, and occasionally to approximately 22 or approximately 26 mm Hg by occluding the portal vein with a pneumatic occluder. Each intravenous pressure was maintained for 90-120 seconds or 4-5 minutes until the diameter increase reached a plateau. Pressure-diameter curves were generated for the control state, during celiac ganglion stimulation, and during local tetrodotoxin or intravenous hexamethonium administration. Diameter was plotted as a function of pressure, and the curves were nonlinear or sigmoid. These results are different from the linear or curvilinear characteristics of the pressure-diameter or pressure-volume relation observed in the pharmacologically or chemically denervated preparation. Tetrodotoxin and hexamethonium attenuated the sigmoid shape of the pressure-diameter curve and shifted it toward the diameter axis of the curve. On the other hand, celiac ganglion stimulation did not change the sigmoid nature of the curve but shifted the curve toward the volume axis.(ABSTRACT TRUNCATED AT 250 WORDS)
Segmental vascular resistance in isolated perfused rat lungs. Influence of vasomotor tone and cyclooxygenase and lipoxygenase inhibition.
Authors: Hillyard R , Anderson J , Raj J U
Published: June 2012

We have determined the profile of pressures in isolated perfused lungs of adult rats and investigated the influence of vasomotor tone and cyclooxygenase and lipoxygenase inhibition on total and segmental vascular resistance. We isolated and blood-perfused lungs of 30 rats (480 +/- 21 g). Group 1 (n = 7) was untreated, group 2 (n = 8) was paralyzed with papaverine, group 3 (n = 11) was treated with indomethacin, and group 4 (n = 4) was treated with indomethacin and U60257, a putative lipoxygenase inhibitor. Blood flow was adjusted initially to raise pulmonary artery pressure to approximately 15 cm H2O and then held constant. Airway and left atrial pressures were held constant at 7 and 8 cm H2O, respectively (zone 3 conditions). In all lungs, we measured pressures in subpleural 20-50-microns-diameter arterioles and venules using the micropuncture servonull technique. Thus, the pulmonary circulation was partitioned into three segments: arteries, microvessels, and veins. In group 1 lungs, arteries presented the largest fractional resistance to flow at 46% of total resistance, with microvessels and veins contributing 34% and 20%, respectively. In group 2 lungs that had no vasomotor tone, total vascular resistance was approximately 27% lower than in group 1 lungs, mainly due to a lower resistance in veins. In indomethacin-treated lungs (group 3) and indomethacin and U60257-treated lungs (group 4), total and segmental vascular resistance was not significantly different from untreated lungs (group 1). We conclude that in isolated perfused rat lungs, arteries are the predominant site of resistance to blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)
Na,K-ATPase in isolated nephron segments in rats with experimental heart failure.
Authors: Wald H , Scherzer P , Popovtzer M M
Published: June 2012

To characterize renal transport of Na+ in heart failure, urinary Na+ excretion (UNaV), aldosterone levels, and Na,K-ATPase activity in isolated nephron segments were determined in three groups: control rats, rats with heart failure and moderate sodium retention, and rats with heart failure and severe sodium retention. Heart failure was induced by a fistula between the aorta and vena cava. For the control group, UNaV was 0.66 +/- 0.04 (mean +/- SEM) mueq/min, and aldosterone was 18.4 +/- 3.5 ng%. Na,K-ATPase activity (in 10(-11) mol/mm/min) was 28.4 +/- 1.1 in the proximal convoluted tubule, 23.3 +/- 1.0 in the proximal straight tubule, 37.4 +/- 1.9 in the medullary thick ascending limb, 40.2 +/- 1.9 in the cortical thick ascending limb, 43.2 +/- 2.2 in the distal convoluted tubule, and 20.5 +/- 0.9 in the cortical collecting duct. For the group with moderate heart failure, UNaV was 0.35 +/- 0.02 (p less than 0.001 versus control), and aldosterone was 15.9 +/- 4.4 (p = NS versus control). Na,K-ATPase activity was unchanged in the proximal convoluted tubule, proximal straight tubule, medullary thick ascending limb, and cortical collecting duct, but it increased in the cortical thick ascending limb to 57.7 +/- 3.1 (p less than 0.001 versus control) and decreased in the distal convoluted tubule to 35.3 +/- 1.2 (p less than 0.005 versus control). For the group with severe heart failure, UNaV was 0.029 +/- 0.016 (p less than 0.001 versus control), and aldosterone was 186.0 +/- 14.8 (p less than 0.001 versus control).(ABSTRACT TRUNCATED AT 250 WORDS)
Simulated blood flow and the effects on prostacyclin production in the dog femoral artery.
Authors: Onohara T , Okadome K , Yamamura S , Mii S , Sugimachi K
Published: June 2012

Effects of blood flow on the production of prostacyclin (PGI2) were examined in the canine femoral artery perfused ex vivo. Each artery was perfused in situ with medium 199, under conditions of simulated blood flow. To simulate the normal and abnormal blood flow waveforms at the same mean flow rate, we developed a flow apparatus capable of making various waveforms by changing the duration when the electromagnetic valve in the circuit was open. Group I (n = 7) was exposed to a steep acceleration waveform followed by a steep deceleration, as the normal flow waveform; group II (n = 7) was exposed to a gentle sloping waveform in the deceleration phase, as the abnormal flow waveform. PGI2 was measured as 6-ketoprostaglandin F1 alpha. PGI2 production was estimated as the cumulative production for the first 5 minutes (acute response) and as the production rate after the first 30 minutes (stable production rate). Under conditions of normal flow, the acute response was 5.87 +/- 2.16 ng/cm2/5 min, whereas under conditions of abnormal flow, the rate was 2.20 +/- 0.27 ng/cm2/5 min (p less than 0.01). Stable production rates were 82.5 and 37.5 pg/cm2/min, respectively (p less than 0.05). Both the acute response and the stable production rate of PGI2 production were greater under conditions of simulated normal flow as compared with findings in the case of an abnormal flow. Our working hypothesis is that the decreased production of PGI2, as well as a deterioration in the implanted graft, under conditions of abnormal blood flow leads to a loss of late patency of the reconstructed arteries.
Phase resetting and entrainment of pacemaker activity in single sinus nodal cells.
Authors: Anumonwo J M , Delmar M , Vinet A , Michaels D C , Jalife J
Published: June 2012

The phase-resetting and entrainment properties of single pacemaker cells were studied using computer simulations in a model of the rabbit sinus nodal cell, as well as using the whole-cell patch-clamp (current-clamp) technique in isolated rabbit sinus nodal cells. Spontaneous electrical activity in the cell model was reconstructed using Hodgkin-Huxley-type equations describing time- and voltage-dependent membrane currents. In both simulations and experiments, single subthreshold current pulses (depolarizing or hyperpolarizing) were used to scan the spontaneous cycle of the cells. Such pulses perturbed the subsequent discharge, producing temporary phasic changes in pacemaker period, and enabled the construction of phase response curves. On the basis of these results, we studied entrainment characteristics of the cells. For example, application of repetitive pulses allowed for phasic changes in the spontaneous cycle and resulted in stable 1:1 entrainment at a range of basic cycle length around the spontaneous cycle, or a 2:1 pattern at basic cycle length values about half the spontaneous cycle length. Between the two entrainment zones, complex Wenckebach-like patterns (e.g., 5:4, 4:3, and 3:2) were observed. The experimental data from the isolated cell were further analyzed from a theoretical perspective, and the results showed that the topological characteristics of the phase-resetting behavior accounts for the experimentally observed patterns during repetitive stimulation of the cell. This first demonstration of phase resetting in single cells provides the basis for phenomena such as mutual entrainment between electrically coupled pacemaker cells, apparent intranodal conduction, and reflex vagal control of heart rate.
Cardiac microcirculatory effects of beta-adrenergic blockade during sympathetic stimulation.
Authors: Cousineau D F , Goresky C A , Rose C P , Schwab A J
Published: June 2012

The effects of beta-adrenergic blockade on cardiac transcapillary exchange were examined at rest and during sympathetic stimulation. Multiple indicator dilution experiments were carried out in closed-chest anesthetized dogs at rest and during carotid occlusion, either under basal conditions or after beta-adrenergic blockade with alprenolol. beta-Adrenergic blockade at rest had no effect on coronary flow or transcapillary exchange in comparison with the control situation, but it abolished the increase in coronary flow and in the permeability/surface area product for labeled sucrose produced by carotid occlusion. High coronary resistance values in beta-blocked animals with carotid occlusion were associated with a high degree of heterogeneity in capillary transit times, but the overall relation between coronary flow and the capillary permeability/surface area product was unchanged. The findings indicate that beta-blockade increases coronary resistance during sympathetic stimulation and, simultaneously, decreases the coronary blood flow and capillary permeability/surface area product while increasing the heterogeneity of capillary transit times.
Effects of protection from pressure on resistance artery morphology and reactivity in spontaneously hypertensive and Wistar-Kyoto rats.
Authors: Bund S J , West K P , Heagerty A M
Published: June 2012

The effects of regional hypotension on femoral resistance artery reactivity and morphology were investigated in spontaneously hypertensive rats (SHR) and control Wistar-Kyoto (WKY) rats. A partially constricting ligature (0.4 mm i.d.) was placed around the left external iliac artery at 5 weeks, which resulted in significantly reduced femoral mean arterial pressures distal to the ligature at 12 and 24 weeks. The femoral mean arterial pressure distal to the ligature in SHR was similar to that in WKY unprotected hind limbs. Resistance arteries (approximately 200 microns i.d.) were taken from unligatured and protected hind limbs and mounted in a myograph for reactivity and morphological measurements. Each experiment therefore utilized one artery distal to a ligature and one from the control hind limb. Histological examination revealed that nuclear density differed neither between strains nor between arteries from protected and unprotected femoral beds. Media thickness, media cross-sectional area, and media/lumen ratios were reduced in arteries from the hypotensive hind limb in SHR and WKY rats at 12 and 24 weeks. Arteries from the protected hind limbs of SHR were structurally indistinguishable from those from the normally perfused WKY vasculature. It is concluded that the medial content and maximal contractile responses of femoral resistance arteries from SHR and WKY rats are mainly determined by the local perfusion pressure and that normalization of perfusion pressure in SHR normalizes resistance artery structure.
Troponin T- and troponin I-like proteins in bovine vascular smooth muscle.
Authors: Zanellato A M , Borrione A C , Saggin L , Giuriato L , Schiaffino S , Sartore S
Published: June 2012

We have tested the hypothesis whether proteins with biochemical and immunochemical properties similar to those of troponin T (TnT) and troponin I (TnI) are expressed in bovine vascular smooth muscle (SM). Three monoclonal anti-TnT antibodies (TT-1, TT-2, and RV-C2) specific for the two isoforms of TnT present in the bovine cardiac muscle and two monoclonal antibodies (TI-1 and TI-5) reacting with cardiac TnI were used in this study. Anti-TnT antibodies were found to be unreactive with 1) skeletal and nonmuscle isoforms of glyceraldehyde-3-phosphate dehydrogenase, a glycolytic enzyme that shares some structural homologies with skeletal TnT, and 2) calponin, a TnT-like calmodulin/tropomyosin binding protein with some antigenic properties in common with TnT. When tested on SM extracts from aorta or coronary arteries by Western blotting, the anti-TnT antibodies were able to react exclusively with one or two polypeptides whose electrophoretic mobility corresponds to the cardiac TnT subunits. Similarly, anti-TnI antibodies specifically recognized a component in the aortic or coronary SM extracts with electrophoretic properties identical to the cardiac TnI. Immunofluorescence analysis performed on the vascular SM cells of bovine aorta, coronary arteries, and intramural branches of coronary vessels confirmed the existence of cardiac troponin immunoreactivity in these tissues. In addition, differences in the distribution of cardiac TnT- and TnI-like proteins were evidenced in nonvascular and vascular SM cells. This study shows for the first time that polypeptides with some structural properties in common with cardiac TnT and TnI can be found in the vascular SM system.
Autoradiographic localization of beta-adrenergic receptors in human large coronary arteries.
Authors: Amenta F , Coppola L , Gallo P , Ferrante F , Forlani A , Monopoli A , Napoleone P
Published: June 2012

The distribution of beta-adrenergic receptors in sections of the human right and left coronary arteries and of the anterior intraventricular branch was studied by the use of combined in vitro radioreceptor binding and autoradiographic techniques. [125I]Cyanopindolol was used as a ligand for beta-adrenergic receptors. Binding of the radioligand to sections of the three coronary arteries under study was saturable, stereoselective, reversible, and displaceable by antagonists and agonists with the rank order of potency expected for beta-adrenergic receptors. Analysis of binding isotherms indicated maximum binding capacities of 41.5 fmol/mg protein for the right coronary artery, 35.4 fmol/mg protein for the left coronary artery, and 25.7 fmol/mg protein for the anterior interventricular branch. Dissociation constants were approximately 35 pM in the arteries examined. The relative amounts of beta 1- and beta 2-receptor subtypes were as follows: 72% beta 1-receptors and 28% beta 2-receptors in the right coronary artery; 65% beta 1-receptors and 35% beta 2-receptors in the left coronary artery; 40% beta 1-receptors and 60% beta 2-receptors in the anterior interventricular branch. The results of autoradiographic analysis revealed a predominance of beta 1-receptors in the medial layer. beta 2-Receptors were localized primarily in the adventitia, in the adventitia-media border, and in the intimal layer. These results should lead to a better understanding of the mechanisms involved in the control of coronary circulation in humans.
Vasopressin increases cytosolic free [Ca2+] in the neonatal rat cardiomyocyte. Evidence for V1 subtype receptors.
Authors: Xu Y J , Gopalakrishnan V
Published: June 2012

Radioligand binding studies of the cardiac arginine vasopressin (AVP) receptor, together with studies on the AVP-evoked alterations in the [Ca2+]i levels, were undertaken using primary cultures of neonatal rat cardiomyocytes. Rapid, reversible, specific, high-affinity and low-capacity binding sites were detected for the agonist, [3H]AVP, and the V1 selective antagonist, d(CH2)5 Tyr (Me)-[3H]AVP (V1 antagonist), radioligands. The V2 selective antagonist radioligand, d(CH2)5 D-Ile des-Gly NH2-[3H]AVP, showed very little binding even at very high concentrations. [3H]AVP and [3H]V1 antagonist specific binding attained equilibrium in 10 minutes at 37 degrees C. The Kd and Bmax values (mean +/- SEM) were [3H]AVP: Kd 1.44 +/- 0.18 nM; Bmax 5,253 +/- 590 sites/cell; [3H]V1 antagonist: Kd 0.96 +/- 0.10 nM; Bmax 6,869 +/- 485 sites/cell. Ki values for a series of AVP-related peptide analogues and antagonists determined by competitive inhibition of [3H]AVP binding were consistent with the saturation data. The results suggest that these cells possess a homogeneous population of V1 subtype AVP receptors. AVP increased [Ca2+]i in a concentration-dependent manner as judged by fura-2 fluorescence. This was completely attenuated by inclusion of the V1 antagonist. The maximal increase in [Ca2+]i evoked by AVP from a resting level of 60 +/- 5 nM was less (250 +/- 35 nM) in comparison to the maximal response evoked by angiotensin II (2,337 +/- 640 nM).(ABSTRACT TRUNCATED AT 250 WORDS)
Disproportionate alpha- and beta-mRNA sodium pump subunit content in canine vascular smooth muscle.
Authors: Allen J C , Medford R M , Zhao X , Pressley T A
Published: June 2012

Total RNA isolated from canine saphenous vein smooth muscle cells was examined for Na+ pump alpha- and beta-mRNA content by three increasingly sensitive methods: Northern analysis, RNase protection assay, and polymerase chain reaction. Northern analysis clearly showed the presence of beta-mRNA. An alpha 1 signal was not demonstrable using either Northern analysis with a 1.5-kb cDNA probe or RNase protection. However, an "alpha 1-like" transcript was detected using polymerase chain reaction with two sets of primers constructed to selected areas of the rat alpha 1-cDNA. These data suggest that beta-mRNA in canine blood vessels is in large excess of the alpha 1-mRNA. This discrepancy may be reflected in the relatively low number of Na+ pump sites in this tissue.
Morphometric evaluation of the contractile apparatus in primary cultures of rabbit cardiac myocytes.
Authors: Decker M L , Behnke-Barclay M , Cook M G , Lesch M , Decker R S
Published: June 2012

Rabbit cardiac myocytes remain quiescent for more than 1 month when cultured at low density. During this period, myofibrillar volume density declines sixfold as myofibrils are disassembled or degraded and are replaced by actin and alpha-actinin-positive, myosin-negative structures that resemble myofibrils but lack thick filaments. Such structures are termed minute myofibrils. The length of the sarcomeres in these altered myofibrils is significantly less than length values obtained from freshly isolated heart cells or from contracting myocytes. A number of high density cultures develop spontaneous, synchronous contraction during the second week of culture. Myofibrillar volume density is stabilized when beating begins, and no further decline is observed in the succeeding weeks of culture. Such contracting myocytes display myofibrils typical of normal heart with no visible evidence of minute myofibrils. The volume density of the transverse tubular system also declines significantly in both beating and nonbeating myocytes, and its reduction appears more closely correlated with cell spreading than with beating per se. No quantitative changes in volume density of mitochondria or sarcoplasmic reticulum could be documented, but the structural organization of the sarcoplasmic reticulum seems to be greatly influenced by the physiological state of the heart cell. The present observations document the importance of mechanical factors in regulating the integrity of the contractile apparatus in cardiac myocytes and emphasize the utility of the cultured heart cell to directly investigate structure-function relations in individual myocytes.
Restricted secretion of a T-lymphocyte chemotactic cytokine by serotonin-stimulated cultured aortic endothelial cells.
Authors: Farber H W , Beer D J
Published: June 2012

The diversity of biologically active molecules produced by vascular endothelium suggests that the endothelial cell is an active participant in numerous physiological responses, including those of the immune system. In fact, the accumulation of T lymphocytes at extralymphatic inflammatory foci represents a series of interactions between lymphocytes and vascular endothelial cells. These interactions, however, may be modulated by other factors, such as vasoactive amines. In the current study, we report that serotonin-stimulated cultured bovine aortic endothelial cells (BAECs) secrete a T-lymphocyte chemotactic cytokine (endothelial cell-derived lymphocyte chemotactic activity [ED-LCA]). Supernatants from BAECs incubated with 10(-7)-10(-4) M serotonin (5-hydroxytryptamine [5-HT]) enhanced T-cell migration, which peaked at 10(-5) M 5-HT (235 +/- 18% control migration). ED-LCA was not stored in an active form in BAECs; its secretion occurred within 60 minutes of exposure to 5-HT and was blocked by two different 5-HT2 receptor antagonists. ED-LCA was not secreted after exposure of BAECs to histamine or angiotensin II, nor was it secreted by either 5-HT-stimulated bovine pulmonary arterial or human umbilical vein endothelial cells. Physicochemical characterization of ED-LCA demonstrated that it was a trypsin-sensitive protein with an apparent molecular mass of 13-15 kDa. Preparative isoelectric focusing demonstrated pIs of 6.0 and 7.5. When applied to a molecular sieve column, the chemotactic activity corresponding to these pIs eluted in the region of 13-15 kDa. Further investigation demonstrated that partially purified ED-LCA was specific for CD4+ and CD8+ T-lymphocyte subsets and did not enhance the migration of neutrophils or monocytes.(ABSTRACT TRUNCATED AT 250 WORDS)
Calcium current depression in isolated human atrial myocytes after cessation of chronic treatment with calcium antagonists.
Authors: Le Grand B , Hatem S , Deroubaix E , Couetil J P , Coraboeuf E
Published: June 2012

The present study investigates the possibility that the slow calcium current of human atrial cardiac cells is modified by chronic treatment (1-24 months) with calcium antagonists (nifedipine, nicardipine, or diltiazem) in a manner different from a simple drug-induced blocking effect. Data from treated patients were recorded approximately 30 hours after cessation of the treatment and were compared with those of nontreated patients. In the treated group, the action potential plateau of atrial fibers was always markedly and irreversibly depressed, and action potential duration measured at 50% repolarization was markedly shortened (81 +/- 12 msec, n = 13) compared with normal values (155 +/- 9 msec, n = 28). In isolated atrial cells, peak calcium current density at +10 mV in treated cells was more than three times as small as that in nontreated cells. Steady-state inactivation relations of calcium current as a function of membrane potential were not significantly different in treated and nontreated cells. In contrast, in treated and nontreated cells superfused with 10(-6) M nifedipine, the curves were markedly shifted toward negative potentials. Cell superfusion with 10(-6) M Bay K 8644 increased calcium current to a larger extent in nontreated cells (sixfold increase) than in treated cells (threefold increase), whereas a 23-fold increase was observed in nontreated cells in which the current had been previously depressed by superfusion with 10(-6) M nifedipine. In contrast to Bay K 8644, 10(-7) M isoproterenol and 10(-8) M angiotensin II increased the calcium current to the same extent in both treated and nontreated groups.(ABSTRACT TRUNCATED AT 250 WORDS)
Inhibitory effects of procainamide on sympathetic nerve activity in humans.
Authors: Rea R F , Hamdan M , Schomer S J , Geraets D R
Published: June 2012

In experimental animals, procainamide causes hypotension and reductions in efferent vasoconstrictor sympathetic outflow that may result from ganglionic blockade or central nervous system sympathetic inhibition. To test the hypothesis that procainamide decreases sympathetic nerve activity (SNA) in humans, we recorded postganglionic SNA in seven normal subjects in the baseline state and during infusions of procainamide HCl at 50 mg/min (loading) and 8 mg/min (maintenance). At the end of the loading infusion, mean arterial pressure (MAP) had decreased from 88.5 +/- 2.4 (mean +/- SEM) to 81.5 +/- 3.2 mm Hg (p less than 0.05), central venous pressure from 6.7 +/- 0.7 to 5.4 +/- 0.9 mm Hg (p less than 0.05), forearm vascular resistance (FVR) from 28 +/- 4.8 to 22.3 +/- 5.1 resistance units (p less than 0.05), and SNA from 259 +/- 47 to 94 +/- 26 units/min (p less than 0.05). These changes persisted during the maintenance infusion. Increased levels of SNA, FVR, and MAP provoked by the cold pressor test were reduced significantly by intravenous procainamide. In eight other subjects, intravenous procainamide HCl (15 mg/kg at 50 mg/min) caused dose-dependent inhibition of SNA that reversed as blood concentrations fell during drug washout. To determine if procainamide causes direct vasodilation, in nine subjects, graded infusions were delivered into the brachial artery at doses that produced no systemic effect. Ipsilateral FVR tended to increase during local intra-arterial infusion of procainamide. These data show that intravenous procainamide causes hypotension, vasodilation, and sympathetic withdrawal. Vasodilation does not result from a direct vasorelaxant effect of the drug.(ABSTRACT TRUNCATED AT 250 WORDS)
Influence of topically applied adrenergic agents on cochlear blood flow.
Authors: Ohlsén K A , Baldwin D L , Nuttall A L , Miller J M
Published: June 2012

This study was designed to assess the role of adrenergic receptors in the control of cochlear blood flow. Laser Doppler flowmetry was used to determine the effects of adrenergic drugs topically applied to the round window membrane of the cochlea. The relative influence of the various receptor types (alpha 1, alpha 2, beta 1, and beta 2) was examined by a selection of agonists and antagonists. The agonists norepinephrine and epinephrine, which have mixed alpha- and beta-receptor effects, and phenylephrine, a strong alpha 1-agonist, all induced a dose-dependent reduction in cochlear blood flow. The agonists isoproterenol (beta-active), salbutamol (alpha 2-active) had no effect on cochlear blood flow. Of the antagonists, when tested alone, only the selective alpha 1-antagonist prazosin had a direct effect on cochlear blood flow, demonstrating an increase in cochlear blood flow. The selective alpha 2-antagonist idazoxan, the beta-antagonist propranolol, and the unselective alpha-antagonist phentolamine had no effect on cochlear blood flow. Interaction studies of agonists and antagonists were performed to specifically define the receptor subclasses responsible for the cochlear blood flow increases with norepinephrine and epinephrine. The results are consistent with the presence of an alpha 1-adrenergic sympathetic control of cochlear blood flow.
Vasoconstriction of canine coronary collateral vessels with vasopressin limits blood flow to collateral-dependent myocardium during exercise.
Authors: Foreman B W , Dai X Z , Bache R J
Published: June 2012

This study was performed to test the hypothesis that active constriction of coronary collateral vessels can worsen hypoperfusion of collateral-dependent myocardium during exercise. Studies were performed in seven adult mongrel dogs in which intermittent followed by permanent occlusion of the left circumflex coronary artery produced an area of collateral-dependent myocardium without gross evidence of infarct. Myocardial blood flow was determined with microspheres while measurement of aortic and distal coronary pressures allowed calculation of collateral and small vessel resistance at rest and during treadmill exercise. The ability of collateral vessel constriction to limit blood flow was assessed by infusion of vasopressin during exercise. During control conditions, blood flow in the collateral zone underwent a subnormal increase during exercise in comparison with the normal zone (1.74 +/- 0.27 versus 2.50 +/- 0.40 ml/min/g, respectively, p less than 0.05). Infusion of vasopressin in a dose that caused no change in normal zone flow (0.01 microgram/kg/min i.v.) produced a 30 +/- 5% further decrease in flow to the collateral zone (p less than 0.01). This decrease in collateral zone flow resulted from a 48 +/- 14% increase in transcollateral resistance in response to vasopressin infusion (p less than 0.01), as well as a 40 +/- 9% increase in small vessel resistance in the collateral zone (p less than 0.01). These data demonstrate that active constriction of both collateral vessels and coronary resistance vessels can contribute to hypoperfusion of collateral-dependent myocardium during exercise.