bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulation of expression of M, B, and mitochondrial creatine kinase mRNAs in the left ventricle after pressure overload in rats.
Authors: Fontanet H L , Trask R V , Haas R C , Strauss A W , Abendschein D R , Billadello J J
Published: June 2012

Pressure overload of the left ventricle induces synthesis of creatine kinase isoenzymes. To determine whether this response is associated with an altered pattern of creatine kinase gene expression, we induced arterial hypertension in rats by suprarenal aortic banding. After 4 days, left ventricular myocardium from hypertensive (n = 7) and normotensive, sham-operated (n = 5) rats was analyzed for isoenzyme activities by chromatography; M and B creatine kinase subunit protein by Western blot; and M, B, and mitochondrial creatine kinase mRNA by Northern blot. Although total creatine kinase activity increased in hypertensive (1,096 +/- 214 IU/g left ventricle) compared with normotensive rats (648 +/- 81 IU/g left ventricle, p less than 0.01), the relative proportions of the cytoplasmic and mitochondrial isoenzymes did not change. The mass of M and B subunits increased 1.9- and 2.7-fold, respectively, in hypertensive compared with control rats. Similarly, the mRNA for M and B subunits as well as mitochondrial creatine kinase increased 2.6-, 1.6-, and 1.8-fold, respectively, in hypertensive rats compared with control rats. Thus, increased energy requirements in acute pressure overload are met by generalized induction of creatine kinase mRNA and subunit protein and not by an isoenzyme switch.
Carnitine palmitoyltransferase in cardiac ischemia. A potential site for altered fatty acid metabolism.
Authors: Pauly D F , Kirk K A , McMillin J B
Published: June 2012

The sensitivity of carnitine palmitoyl coenzyme A (CoA) transferase I to inhibition of its activity by malonyl-CoA is progressively reduced in mitochondria isolated from ischemic cardiac cells as blood flow decreases to 30% or less of the preocclusion flow. The activity of carnitine palmitoyl-CoA transferase I in mitochondria isolated from nonischemic cardiac cells demonstrates incomplete inhibition, even at high concentrations of malonyl-CoA. Kinetic analyses of these data gave results most consistent with the expression of two overt enzyme activities: one activity that is sensitive to inhibition by malonyl-CoA and one activity that demonstrates little or no sensitivity to such inhibition. The decrease in malonyl-CoA-sensitive activity associated with ischemia results from a 13% decrease in the activity of the sensitive component and a corresponding 13% increase in the activity of the insensitive component. Decreased sensitivity of ischemic carnitine palmitoyl-CoA transferase I to inhibition by malonyl-CoA, together with potential fluctuations in the content of malonyl-CoA in tissue, would increase the synthesis of palmitoylcarnitine during ischemia and facilitate return to the use of fatty acid as a preferred metabolic fuel on reperfusion. This apparent conversion occurs concomitantly with a decrease in the free protein thiol content of the mitochondrial membranes isolated from ischemic cardiac cells. Treatment of the mitochondria from ischemic cardiac cells with dithiothreitol in vitro partially reverses the loss in sensitivity to malonyl-CoA, suggesting the possible role of thiol oxidation in the altered metabolism of ischemic mitochondria. Western blot analysis of these mitochondria using an antibody against carnitine palmitoyltransferase II purified from beef heart demonstrates a 68-kDa protein, which under ischemic conditions apparently is decreased by 2 kDa. These results are more indicative of a modification in protein folding of carnitine palmitoyltransferase than proteolytic changes during ischemia.
Comparison of dextran and hematocrit effects in the pulmonary microcirculation.
Authors: Raj J U , Anderson J
Published: June 2012

We have compared the effects of an increase in perfusate viscosity induced by dextran and by hematocrit (Hct) on segmental vascular resistance in the pulmonary circulation and the effect of flow on microvascular resistance in lungs perfused with dextran and red blood cells. We isolated and perfused lungs of 39 neonatal rabbits weighing 670 +/- 250 g. To determine the effect of dextran, group 1 (n = 8) lungs were perfused with both 5% and 20% dextran 70 solutions (Hct, approximately 25%); to determine the effect of Hct, group 2 (n = 5) lungs were perfused alternately with 5% and 40% Hct solutions (5% dextran 70). In group 1 and group 2 lungs, experiments were done at constant flow and pressure. Group 3 and group 4 (each n = 4) lungs were perfused with 5% and 20% dextran 70, respectively (0 Hct); group 5 (n = 5), with 10% dextran 70; group 6 (n = 7), with 5% dextran 500; and group 7 (n = 6), with 20% dextran 70 (Hct, approximately 5%). All lungs were perfused in zone 3; airway and left atrial pressures were 6 and 8 cm H2O, respectively. To partition the circulation, we measured pressures in the pulmonary artery and left atrium continuously and pressures in 20-50-microns arterioles and 20-50-microns venules by micropuncture. We found that an increase in both the concentration and molecular weight of dextran increased perfusate viscosity and the resistance in all three longitudinal vascular segments: arteries, microvessels, and veins.(ABSTRACT TRUNCATED AT 250 WORDS)
Thrombin modulates phosphoinositide metabolism, cytosolic calcium, and impulse initiation in the heart.
Authors: Steinberg S F , Robinson R B , Lieberman H B , Stern D M , Rosen M R
Published: June 2012

Thrombin stimulates phosphoinositide hydrolysis and increases cytosolic calcium in several types of cells. To determine whether thrombin exerts similar stimulatory actions in the heart and whether this mechanism is linked to changes in cardiac electrical activity, the effects of thrombin on several biochemical and electrophysiological parameters were examined. In neonatal rat ventricular myocyte cultures freed of fibroblast contamination by irradiation, thrombin rapidly induced the breakdown of phosphoinositides. Formation of inositol trisphosphate was detectable within 5 seconds and was followed by the sequential accumulation of inositol bisphosphate and inositol monophosphate. The effect of thrombin to stimulate phosphoinositide hydrolysis was inhibited by hirudin, but not by propranolol, prazosin, or pretreatment with pertussis toxin. The inositol phospholipid response was unassociated with changes in intracellular cAMP levels. To determine the electrophysiological effects of thrombin, we used microelectrode techniques to study canine Purkinje fibers. Thrombin increased the beating rate of fibers depolarized using barium, but not those at normal maximal diastolic potential. In addition, thrombin prolonged the action potential duration in fibers driven at a constant cycle length. This response was inhibited by hirudin and nisoldipine, but not by propranolol, prazosin, or pretreatment with pertussis toxin. Thrombin also augmented cesium-induced early afterdepolarizations. Using the fluorescent calcium indicator fura-2, we demonstrated that thrombin increased the beating rate, diastolic calcium, and peak systolic calcium of spontaneously contracting cultured ventricular myocytes. Cytosolic calcium also increased in both rat ventricular myocytes and canine Purkinje myocytes that were electrically driven at a constant basic cycle length, indicating that thrombin modulates cellular calcium metabolism independent of its actions to enhance automaticity. Taken together, these findings demonstrate several novel biological actions of thrombin in the mammalian heart that may be functionally related. The actions of thrombin to enhance automaticity and prolong repolarization may contribute to the electrical abnormalities observed in the setting of myocardial ischemia and infarction.
Effects of quinapril, a new angiotensin converting enzyme inhibitor, on left ventricular failure and survival in the cardiomyopathic hamster. Hemodynamic, morphological, and biochemical correlates.
Authors: Haleen S J , Weishaar R E , Overhiser R W , Bousley R F , Keiser J A , Rapundalo S R , Taylor D G
Published: June 2012

The effect of chronic therapy with quinapril on the temporal progression of left ventricular failure and survival was assessed in the CHF 146 cardiomyopathic (CM) hamster, which is an idiopathic model of congestive heart failure. Age-matched Golden Syrian (GS) hamsters served as normal controls. Quinapril was administered in the drinking water at average daily doses of 10.2, 112.4, and 222.4 mg/kg/day. In untreated CM hamsters, in vitro left ventricular performance progressively deteriorated with increasing age beginning at roughly 180 days. This decline in left ventricular performance was accompanied by a decrease in coronary flow and an increase in left ventricular volume. Administration of quinapril from 180 to 300 days of age prevented the decline of in vitro left ventricular contractile performance and coronary flow and also reduced the age-dependent increases in left ventricular volume. The cardioprotective effects of quinapril were observed at doses of 112.4 and 222.4 mg/kg/day but not at 10.2 mg/kg/day. Lung angiotensin converting enzyme activity was significantly inhibited by quinapril in GS and CM hamsters at 240 and 300 days of age at all dose levels. In contrast, significant inhibition of ventricular angiotensin converting enzyme activity was observed consistently at doses of 112.4 and 222.4 mg/kg/day quinapril but not at 10.2 mg/kg/day. In the survival protocol, CM and GS hamsters were treated with vehicle or quinapril (100 mg/kg/day) from 180 to 522 days of age. During the initial 210 days of treatment (from 180 to 390 days of age) 78.3% of the vehicle-treated CM hamsters died compared with 27.7% of quinapril-treated CM hamsters. Quinapril increased the median survival time of CM hamsters by 32.9% (112 days). It is concluded that chronic quinapril therapy exerts a significant cardioprotective effect and also increases survival.
Intracellular calcium and ventricular fibrillation. Studies in the aequorin-loaded isovolumic ferret heart.
Authors: Kihara Y , Morgan J P
Published: June 2012

To elucidate the role of changes in [Ca2+]i in the induction of ventricular fibrillation (VF), Ca2+i signals, epicardial electrical potentials, and isovolumic left ventricular pressure were simultaneously recorded in isolated intact ferret hearts loaded with aequorin, a bioluminescent protein. When the preparations were perfused with 3 microM acetylstrophanthidin and 8 mM Ca2+, or with a low Na+ solution (18 mM Na+, 100 mM Li+), spontaneous transitions to the VF state were consistently observed within a short period of time. The initiation of spontaneous VF was preceded by development of a Ca2+i overload state, coincidental with the ascending phase of diastolic Ca2+i oscillations, and was followed by further elevation in Ca2+i levels, which were associated with augmented Ca2+i oscillations of a saw-toothed pattern. Pretreatment with 10 microM ryanodine, which blocked Ca2+i oscillations in the preparation, did not eliminate inducibility of VF by means of AC electrical stimulations; however, VF no longer occurred spontaneously, and the threshold for VF induction increased markedly. In the absence of a state of Ca2+i overload, spontaneous defibrillation occurred within a minute after the initiation of VF. We conclude that 1) VF can be induced in the absence of Ca2+i oscillations; however, 2) Ca2+i oscillations play a crucial role as a trigger for VF and therefore are an important determinant of the vulnerability to VF; and 3) the augmented Ca2+i oscillations after the transition to VF state may support the maintenance of this type of arrhythmia.
Role of the sarcolemma in triggered propagated contractions in rat cardiac trabeculae.
Authors: Daniels M C , Fedida D , Lamont C , ter Keurs H E
Published: June 2012

We have recently described that after contractions propagate through multicellular cardiac muscle preparations. These propagating contractions are triggered in damaged regions of rat right ventricular trabeculae during relaxation of electrically stimulated twitches. Propagation of triggered contractions has been attributed to calcium ions that diffuse along the preparation, causing calcium-induced calcium release from the sarcoplasmic reticulum in adjacent cells. In the present study we have investigated a possible role of the sarcolemma and delayed afterdepolarizations (DADs) in the initiation and propagation of triggered propagated contractions (TPCs) in multicellular preparations. We studied whether 1) TPCs are accompanied by delayed sarcolemmal depolarizations, 2) such depolarizations mediate local contraction, and 3) an intact sarcolemma is required for propagation of contractions. TPCs that remained stable for prolonged periods of time could be induced by trains of 15 stimuli (2 Hz, 15-second intervals) at lowered temperature (19-21 degrees C) of the superfusing Krebs-Henseleit medium and a [Ca(2+)]o of 1.0-1.5 mM. Although TPCs could be induced at 38 degrees C and a [Ca2+]o of 3.0-4.0 mM, they disappeared within 10 minutes. Force was measured with a silicon strain gauge; length and shortening of sarcomeres were measured at two sites of the muscle using laser diffraction techniques. Membrane potential was measured with flexible microelectrodes. Saponin was used to selectively render the sarcolemma permeable to small ions and molecules. Propagation velocity of TPCs in intact trabeculae varied from 1.7 to 13.4 mm/sec at 19-21 degrees C. TPCs were accompanied by DADs that could reach threshold and induce triggered arrhythmias. Changes in latency, duration, and force of TPCs, induced by changing [Ca(2+)]o or the number of conditioning stimuli, were closely matched by changes in latency, duration, and amplitude of DADs; DADs consistently preceded TPCs, on average by 60 msec. Local heating of the muscle, by applying a current through an insulated platinum wire (diameter 100 microns) that touched the muscle, interrupted propagation of TPCs reversibly. DADs were, in the absence of a local contraction, still recorded distal to the heated site. In muscles that were treated with saponin and exposed to solutions approximating the intracellular milieu, spontaneously occurring local contractions that propagated in both directions (at velocities of 70-200 microns/sec) were elicited at a bathing calcium concentration of approximately 0.6 microM. Below this threshold, propagated contractions could be triggered by pressure ejection of a calcium-containing solution from a microelectrode positioned close to the trabecula.(ABSTRACT TRUNCATED AT 400 WORDS)
Relative roles of cardiac and arterial baroreceptors in vasopressin regulation during hemorrhage in conscious dogs.
Authors: Shen Y T , Cowley A W , Vatner S F
Published: June 2012

To determine the relative roles of cardiac and sinoaortic baroreceptors in mediation of arginine vasopressin (AVP) release, hemorrhage was performed in five groups of conscious splenectomized dogs: 1) all nerves intact; 2) either chronic surgical or acute pharmacological (intrapericardial lidocaine) cardiac denervation (CD); 3) chronic sinoarotic denervation (SAD); 4) combined chronic sinoartic denervation plus either chronic or acute cardiac denervation (SAD + CD); and 5) all nerves intact, but with ganglionic blockade. Hemorrhage (0.5 ml/min/kg) reduced mean arterial pressure similarly in the intact and CD groups. Decreases in mean arterial pressure were augmented in SAD, SAD + CD, and ganglion-blocked groups compared with responses in intact and CD groups. There were no differences in responses of plasma AVP to hemorrhage in the intact and CD groups, but the AVP response was significantly blunted in the SAD + CD group as compared with SAD alone. When compared during the early stage of hemorrhage, at the same reduction in mean arterial pressure, the rise in AVP was greater in the ganglion-blocked group than in the SAD + CD group, but was less than in the intact group. With a protocol to reduce mean arterial pressure by 20 mm Hg over the same period (42 +/- 0.6 minutes) in four of the groups, the blood volume required to reduce mean arterial pressure by 20 mm Hg was similar in the intact (20 +/- 1 ml/kg) and CD (21 +/- 1 ml/kg) groups, but was less in the SAD (12 +/- 1 ml/kg) and SAD + CD (12 +/- 1 ml/kg) groups. Again, similar increases were observed in AVP between the intact (50 +/- 9 pg/ml) and CD (51 +/- 9 pg/ml) groups, whereas increases in AVP were diminished in the SAD (11 +/- 3 pg/ml) and SAD + CD (7 +/- 2 pg/ml) groups. In the presence of an AVP antagonist, decreases in mean arterial pressure and increases in total peripheral resistance with hemorrhage were affected similarly in both the intact and CD groups, whereas hemodynamic impairment by AVP blockade was less marked in the SAD and SAD + CD groups. These results indicate that cardiac receptors are not the major regulators of AVP release during progressive hemorrhage in conscious dogs. However, when the complicating influences of sinoaortic reflexes were eliminated, a modest role for cardiac receptors was uncovered.
Effect of continuous enhanced vagal tone on atrioventricular nodal and sinoatrial nodal function in humans.
Authors: Page R L , Tang A S , Prystowsky E N
Published: June 2012

A constant intravenous infusion of phenylephrine (0.74 +/- 0.41 micrograms/kg/min) was given to 10 patients to cause a continuous augmentation in reflex vagal tone. After the infusion, the diastolic blood pressure increased from 76 +/- 7 to 89 +/- 11 mm Hg (p less than 0.01). The sinus cycle length and atrial-His (AH) interval were measured, and incremental atrial pacing was performed before and during phenylephrine infusion until atrioventricular (AV) nodal block was achieved. For each patient, the AV nodal function curve (i.e., the AH interval plotted as a function of the atrial pacing cycle length) was compared during both the control state and phenylephrine infusion; the AH intervals during each condition at chosen short (AHS) and long (AHL) cycle lengths were compared. The sinus cycle length increased during phenylephrine infusion from 941 +/- 294 to 1,115 +/- 347 msec (p = 0.013). The AH interval during sinus rhythm was not significantly prolonged (77 versus 82 msec, p = NS). The shortest atrial pacing cycle length yielding 1:1 AV nodal conduction increased during phenylephrine infusion from 412 +/- 120 to 575 +/- 211 msec (p less than 0.01). Of note, the degree of sinus cycle length prolongation did not correlate with the degree of prolongation in the shortest atrial pacing cycle length yielding 1:1 AV nodal conduction. The AV nodal function curve was shifted markedly to the right and only slightly upward.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of digitalis glycosides on norepinephrine release in the heart. Dual mechanism of action.
Authors: Kranzhöfer R , Haass M , Kurz T , Richardt G , Schömig A
Published: June 2012

The effect of ouabain on exocytotic and nonexocytotic norepinephrine release was investigated in perfused rat and guinea pig hearts. The overflow of endogenous norepinephrine and its neuronal metabolite 3,4-dihydroxyphenylethyleneglycol (DOPEG) was determined by high-pressure liquid chromatography. DOPEG served as the indicator of free axoplasmic norepinephrine concentrations. The overflow of the norepinephrine cotransmitter neuropeptide Y (NPY) was determined by radioimmunoassay and NPY was used as marker for exocytotic release. Electrical stimulation of the left stellate ganglion resulted in exocytotic norepinephrine release in rat and guinea pig hearts. Ouabain caused an increase in stimulation-induced norepinephrine overflow from rat and guinea pig hearts by 40%. However, overflow of NPY was decreased by 40%, indicating a reduced exocytosis rate. Ouabain increased both norepinephrine and NPY overflow, suggesting enhancement of exocytosis, when neuronal catecholamine uptake (uptake1) was blocked by desipramine or when presynaptic alpha 2-adrenoceptors were inhibited by yohimbine. The results demonstrate an interaction of ouabain with both calcium-dependent exocytosis and uptake1 of norepinephrine. Under calcium-free conditions, ouabain or potassium-free perfusate resulted in norepinephrine release from hearts when the axoplasmic norepinephrine concentration was elevated by the reserpinelike agent Ro 4-1284. This release was independent from neural activity, not accompanied by NPY overflow, and suppressed by the uptake1 blocker desipramine. These findings are in keeping with carrier-mediated nonexocytotic norepinephrine release that is caused by reversal of the transport direction of the uptake1 carrier. During myocardial ischemia nonexocytotic norepinephrine release was accelerated and enhanced by inhibition of Na+,K(+)-ATPase before ischemia. This study demonstrates the potential of digitalis glycosides to interact both with transmitter exocytosis and with the neuronal catecholamine transport system by Na+,K(+)-ATPase inhibition. Interaction with the catecholamine transport system involves both inhibition of norepinephrine inward transport and induction of norepinephrine outward transport, resulting in nonexocytotic norepinephrine release.
Role of cardiac ATP-regulated potassium channels in differential responses of endocardial and epicardial cells to ischemia.
Authors: Furukawa T , Kimura S , Furukawa N , Bassett A L , Myerburg R J
Published: June 2012

Epicardial cells are more susceptible to the electrophysiological effects of ischemia than are endocardial cells. To explore the ionic basis for the differential electrophysiological responses to ischemia at the two sites, we used patch-clamp techniques to study the effects of ATP depletion on action potential duration and the ability of ATP-regulated K+ channels in single cells isolated from feline left ventricular endocardial and epicardial surfaces. During ATP depletion by treatment with 1 mM cyanide (CN-), shortening of action potential durations was significantly greater in epicardial cells than in endocardial cells. Thirty minutes after initiating exposure to 1 mM CN-, action potential duration at 90% repolarization was reduced to 0.70 +/- 0.12 of the control value for endocardial cells versus 0.39 +/- 0.18 for epicardial cells (p less than 0.01), and action potential duration at 20% repolarization was reduced to 0.72 +/- 0.13 for endocardial cells versus 0.12 +/- 0.09 for epicardial cells (p less than 0.01). In both endocardial and epicardial cells, the shortening of action potential by CN- treatment was partially reversed by 0.3 microM glibenclamide; the magnitude of reversal, however, was much greater in epicardial cells. After exposure to 1 mM CN-, the activity of ATP-regulated K+ channels in cell-attached membrane patches was significantly greater in epicardial cells than in endocardial cells. To study the dose-response relation between ATP concentration and open-state probability of the channels, intracellular surfaces of inside-out membrane patches containing ATP-regulated K+ channels were exposed to various concentrations of ATP (10-1,000 microM). The concentration of ATP that produced half-maximal inhibition of the channel was 23.6 +/- 21.9 microM in endocardial cells and 97.6 +/- 48.1 microM in epicardial cells (p less than 0.01). These data indicate that ATP-regulated K+ channels are activated by a smaller reduction in intracellular ATP in epicardial cells than in endocardial cells. The differential ATP sensitivity of ATP-regulated K+ channels in endocardial and epicardial cells may be responsible for the differential shortening in action potentials during ischemia at the two sites.
Priming by platelet-activating factor of endotoxin-induced lung injury and cardiovascular shock.
Authors: Rabinovici R , Esser K M , Lysko P G , Yue T L , Griswold D E , Hillegass L M , Bugelski P J , Hallenbeck J M , Feuerstein G
Published: June 2012

Platelet-activating factor (PAF) is a glycerophospholipid known for its unusual potent vasoactive and proinflammatory activities. The present study examined whether PAF might serve as a priming factor in endotoxin-induced tumor necrosis factor-alpha (TNF alpha) synthesis, cardiovascular shock, and lung injury in anesthetized rats. Intravenous infusion of PAF (1 pmol/kg/min for 60 minutes, n = 5) alone or endotoxin (0.1 micrograms/kg i.v. bolus, n = 5) failed to alter blood pressure, serum TNF alpha and thromboxane B2, platelet and leukocyte count, and hematocrit, nor was lung histology, myeloperoxidase activity, and water content changed. In contrast, the combined administration of PAF and endotoxin markedly elevated serum TNF alpha (1,359 +/- 362 pg/ml, n = 5, p less than 0.01) and thromboxane B2 (43 +/- 5 pg/100 microliters, n = 8, p less than 0.01) along with hypotension, hemoconcentration, leukopenia, and thrombocytopenia. Most notably, the combined regimen caused neutrophil aggregation, adhesion, and accumulation into the lung parenchyma along with platelet-fibrin deposits in postcapillary venules, pulmonary edema, and increased lung myeloperoxidase activity. The role of PAF in this process was confirmed by 1) the prevention of the priming effect by pretreatment with the PAF antagonist BN 50739 (n = 5), and 2) the failure of lyso-PAF, the cardinal nonactive PAF-metabolite, to prime for endotoxin-induced production of TNF alpha (n = 4). These data suggest that PAF could serve as a key mediator in priming for endotoxin-induced tissue injury, especially the typical pulmonary pathophysiology of adult respiratory distress syndrome, a severe pathological outcome of septic shock, burns, and multiple organ injury.
Role of intrarenal angiotensin II and alpha-adrenoceptors in renal vasoconstriction with acute hypoxemia and hypercapnic acidosis in conscious dogs.
Authors: Rose C E , Vance J E , Dacus W S , Brashers V L , Peach M J , Carey R M
Published: June 2012

To evaluate our previous observation of renal vasoconstriction during combined acute hypoxemia and hypercapnic acidosis preceded by acute hypoxemia, we studied 13 conscious mongrel uninephrectomized dogs with chronic renal catheters and controlled sodium intake (80 meq/day for 4 days). Five dogs were studied during combined acute hypoxemia (PaO2, 37 +/- 1 mm Hg) and hypercapnic acidosis (PaCO2, 59 +/- 1 mm Hg; pH 7.20 +/- 0.01). Each dog was studied during infusion of 1) the intrarenal vehicle (n = 5), 2) the intrarenal alpha 1-antagonist prazosin (0.2 micrograms.kg-1.min-1, n = 5), 3) intrarenal [Sar1,Ala8]angiotensin II (70 ng.kg-1.min-1, n = 5), and 4) intrarenal prazosin and [Sar1,Ala8]angiotensin II (n = 4). Immediate induction of combined hypoxemia and hypercapnic acidosis after control measurements during intrarenal vehicle infusion resulted in a decrease in effective renal plasma flow and glomerular filtration rate, increase in renal vascular resistance, and decrease in filtered sodium load in the first 20 minutes of the blood gas derangement. Intrarenal administration of [Sar1,Ala8]angiotensin II failed to reverse the effects of the combined blood gas derangement on renal function. In contrast, intrarenal prazosin administration either alone or in combination with [Sar1,Ala8]angiotensin II abrogated the increase in renal vascular resistance, decrease in glomerular filtration rate, and fall in filtered sodium load. These studies identify a major role for alpha 1-adrenoceptors in the renal vasoconstriction during combined hypoxemia and hypercapnic acidosis.
Effect of reduced blood flow on alpha 1- and alpha 2-adrenoceptor constriction of rat skeletal muscle microvessels.
Authors: McGillivray-Anderson K M , Faber J E
Published: June 2012

Adrenergic constriction of skeletal muscle arterioles, particularly small terminal arterioles, is opposed by decreased blood flow or increased metabolic rate. Our previous studies indicate that neural constriction of large arterioles, which have both postjunctional alpha 1- and alpha 2-adrenoceptors, is mediated by alpha 1-receptors; small arterioles depend on alpha 2-receptors. Also, alpha 2, but not alpha 1, constriction is reduced by acidosis. Differential sensitivity of alpha 1 versus alpha 2 constriction to metabolic signals such as H+ may underlie the sensitivity of arteriolar adrenergic constriction to metabolic inhibition. To examine this hypothesis, we studied the effect of reduced perfusion on alpha 1- versus alpha 2-mediated constriction of large arterioles and venules. Intravital microscopy of rat cremaster skeletal muscle was used to obtain concentration-response curves for phenylephrine (alpha 1-agonist) and UK-14,304 (alpha 2-agonist). Thirty percent reduction in cremasteric artery flow by venous outflow obstruction had no effect on baseline diameter, indicating no effect on "intrinsic tone." Reduced perfusion also had no effect on arteriolar or venular sensitivity to phenylephrine or venular sensitivity to UK-14,304 but significantly attenuated arteriolar response to UK-14,304. To examine a possible mechanism for the selective inhibition of alpha 2 constriction by acidosis, we determined the effect of acidosis on the partial alpha 1-agonist St587. Like alpha 2 constriction, St587-mediated constriction of arterioles was reduced during acidosis and was attenuated by nifedipine.(ABSTRACT TRUNCATED AT 250 WORDS)
Resonance. The missing phenomenon in hemodynamics.
Authors: Wang Y Y , Chang S L , Wu Y E , Hsu T L , Wang W K
Published: June 2012

To simulate a short segment of the aorta, we studied wave propagation in an elastic tube with a side branch balloon. The small balloon simulated the organ (group of arterioles). Ligation of this side branch would reduce the moduli of the higher harmonics when the length of the side branch was appropriate. Electrical analogy of vessels was used to analyze this phenomenon. This simulation can explain the ligation results we found in rats. It may also clarify the discrepancies between the prediction of the Womersley equation and the experimental results. We suggest that the aorta and the closely attached organ can produce coupled oscillation; theoretically, this structure is equivalent to a resonance circuit.
Mechanism of sustained mechanical alternans. Effect of variations in ventricular billing volume.
Authors: Adler D , Nikolic S , Sonnenblick E H , Yellin E L
Published: June 2012

This study investigations the phenomenon of sustained mechanical alternans (SMA) through the use of quantitative criteria. Discrete analysis is used to demonstrate that the hemodynamic variables during SMA are governed by a simple mathematical relation. The analysis shows that the value of the slope created by the two alternating beats on the stroke volume (SV)-end-diastolic volume (EDV) plane is gamma = (mu - 1) (1 + beta)/(mu - beta), where mu = SVs/SVw, and SVs and SVw denote the strong and weak beats, respectively, in the presence of one contractile state, and the beats associated with the higher and lower contractile states, respectively, in the presence of two alternating contractile states; beta = FVs/FVw, where FVs and FVw are the filling volumes after SVs and SVw, respectively. This equation is valid, whether SMA is exhibited in the presence of one or two contractile states and irrespective of the SV-EDV functional relation. Assuming constant afterload, a criterion based on this slope (gamma) is described to determine if SMA is caused by variations in EDV and FV. The slope of the SV-EDV curve in the presence of one contractile state (denoted as gamma) was determined directly (34 runs in eight dogs) by preventing FV in a beat, after a steady state, using a remote-controlled mitral valve. The slope gamma = 0.892 +/- 0.078 was found to agree with data in the literature. In 10 other dogs, mitral flow and aortic flow were measured in 55 series of SMA. In 51 series, gamma was greater than 1. Because the experimental slope in the presence of one contractile state, gamma, is smaller than or equal to 1, the possibility that one contractile state is involved in this series is rejected. On the other hand, when two contractile states are involved, the slope that the two successive beats create on the SV-EDV plane, gamma, is determined by connecting the two SV-EDV relations. This slope tends to be greater than 1. Thus, in these 51 series, SMA cannot be explained as a result of the Frank-Starling mechanism and variations in FV but as a result of two alternating contractile states. In the other four series, the value of gamma can be compatible either with the presence of one contractile state or with two alternating contractile states. This quantitative analysis enables the classification of the various types of SMA into subcategories with well-defined features. The quantitative analysis presented here shows that the common genesis of SMA is an alternating contractile state.
Frog cardiac calsequestrin. Identification, characterization, and subcellular distribution in two structurally distinct regions of peripheral sarcoplasmic reticulum in frog ventricular myocardium.
Authors: McLeod A G , Shen A C , Campbell K P , Michalak M , Jorgensen A O
Published: June 2012

Calsequestrin is a calcium-binding protein known to sequester calcium accumulated in the sarcoplasmic reticulum (SR) of muscle cells during relaxation. In the present study, we used affinity-purified antibodies to chicken cardiac calsequestrin to identify a 60,000-Da calsequestrin in frog myocardium. Like previously identified cardiac calsequestrins, it is enriched in cardiac microsomes, it is enriched by biochemical procedures previously used to purify cardiac and skeletal calsequestrins, and it exhibits a pH-dependent shift in its apparent Mr on a two-dimensional gel system. Finally, the NH2-terminal amino acid sequence of this 60,000-Da immunoreactive protein purified by fast protein liquid chromatography was identical to that of rabbit skeletal and canine cardiac calsequestrin. Thus, we conclude that this protein corresponds to the calsequestrin isoform in frog ventricular muscle. Frog calsequestrin was localized in discrete foci present at the periphery but absent from the central regions of frog ventricular myocytes as determined by immunofluorescence labeling. Immunoelectron microscopic labeling demonstrated that calsequestrin was confined to the lumen of two structurally distinct regions of the SR, where it was localized in the subsarcolemmal region of the myofibers. One of these appeared to correspond to the terminal SR previously reported to be closely apposed to the sarcolemma of frog myofibers. The other region, although close to the sarcolemma, was not physically joined to it and appeared to correspond to corbular SR. It generally is believed that frog cardiac SR does not provide activator Ca2+ required for excitation-contraction coupling. However, the identification of a calsequestrin isoform very similar to mammalian cardiac calsequestrin that is confined to specialized regions of frog cardiac SR lends support to the idea that frog cardiac SR has the ability to store Ca2+ and thus function in some capacity in frog cardiac muscle contraction.
Contribution of endogenous endothelin to the extension of myocardial infarct size in rats.
Authors: Watanabe T , Suzuki N , Shimamoto N , Fujino M , Imada A
Published: June 2012

Pathophysiological roles of endogenous endothelin have been studied from the viewpoint of its contribution to the extension of myocardial infarct size. A monoclonal antibody against endothelin 1 (AwETN40) suppressed changes induced by endothelin 1 and endothelin 2 but did not modify those by endothelin 3 in vivo or in vitro. Effects of AwETN40 on myocardial infarct size were investigated. Coronary ligation (1 hour) and reperfusion (24 hours) in rats caused infarction in 35% of the left ventricle. Repetitive or single administration of AwETN40 reduced the infarct size; an intravenous injection of 22.5 mg/kg of the antibody 5 minutes after coronary occlusion or 5 minutes before reperfusion reduced the size by 38% or 31% of the control, respectively. Plasma and tissue endothelin 1 and plasma big endothelin 1 in rats were measured at various stages after occlusion. Plasma endothelin 1 showed a fourfold increase 10 minutes after reperfusion (from 1.02 to 3.96 pg/ml) and had returned to the control value after 8 hours. Plasma big endothelin 1 showed changes similar to those of plasma endothelin 1. No significant changes in plasma endothelin 2 and endothelin 3 were observed. Cardiac tissue contained seven times as much endothelin 1 as the control value 1 hour after reperfusion (4.59 versus 33.1 pg/g tissue), and a high concentration (13.2 pg/g tissue) was maintained even after 48 hours. We concluded that an increase in endogenous endothelin 1 plays an important role in the extension of myocardial infarct size.
Rapid attenuation ("fade") of the chronotropic response during vagal stimulation in the canine newborn. Evidence for a prominent neuropeptide Y effect.
Authors: Yamasaki S , Stolfi A , Mas M S , Fox L S , Pickoff A S
Published: June 2012

We studied the time-dependent changes in the response of heart rate (sinus cycle length) to 30-second trains of vagal stimulation (8 Hz), repeated every 2 minutes, in canine neonates aged 7.1 +/- 2.5 (mean +/- SD) days. The first vagal train prolonged the sinus cycle length by 58 +/- 35%, but the response was attenuated during subsequent trains (98 +/- 5% inhibition of the vagal response after only 6.4 +/- 1.7 trains). After 40 minutes, complete restoration of the chronotropic response could be demonstrated. Receptor desensitization could be excluded as the reason for the attenuation by demonstrating preserved responses to exogenous acetylcholine. Neuropeptide Y, a sympathetic cotransmitter that has been shown to attenuate parasympathetic responses (thought to be the result of inhibition of the release of acetylcholine from parasympathetic nerve terminals), was administered (50 micrograms/kg) to eight newborns. Exogenous neuropeptide Y resulted in a complete inhibition of the chronotropic response to vagal stimulation, with restoration of the chronotropic response occurring after 60 minutes. Thus, exogenous neuropeptide Y mimicked the effect of repetitive vagosympathetic trunk stimulation; this finding suggested that neuropeptide Y release from sympathetic nerves during repetitive vagosympathetic trunk stimulation may have resulted in the observed attenuation of the vagal chronotropic response. To test this hypothesis, seven other newborns underwent chemical sympathectomy (50 mg/kg i.p. 6-hydroxydopamine for 3 days, tyramine verified), and in these newborns, stable chronotropic responses to repetitive vagosympathetic trunk stimulation were observed (inhibition of vagal response was 0 +/- 18% after 10 stimulus trains).(ABSTRACT TRUNCATED AT 250 WORDS)
Morphology of electrophysiologically identified junctions between Purkinje fibers and ventricular muscle in rabbit and pig hearts.
Authors: Tranum-Jensen J , Wilde A A , Vermeulen J T , Janse M J
Published: June 2012

Purkinje fiber-ventricular muscle (PV) junctions were identified by extracellular recording in isolated, superfused preparations from rabbit and pig hearts. Microelectrode recordings from different cell types at the PV junctions were obtained, and the cells recorded from were retrieved microscopically. To this end 26 tissue blocks were serially sectioned at 4 microns. Microscopic identification of the very cell recorded from was obtained in five of seven Purkinje, five of 16 transitional, and two of two ventricular muscle cell recordings. In addition, some tissue blocks from both junctional and nonjunctional sites identified only by extracellular recording were examined in serial sections. Transitional cells in the rabbit heart are thin, broad bandlike cells (30-35 by 3-5 microns) arranged in one or two sheets in the subendocardium between the Purkinje layer and ventricular mass. Transitional cells are coupled via short, thin strands to both Purkinje and ventricular muscle cells. A second type of PV coupling was observed frequently in the pig, but in only one of 21 cases in the rabbit. Here, a short, linear segment of small transitional cells connected large-diameter Purkinje cells to ventricular muscle cells. Distances found between Purkinje-transitional cell coupling sites and transitional cell-ventricular muscle coupling sites varied from 100 to 1,000 microns in the rabbit heart and from 50 to several hundred micrometers in the pig heart. Action potentials from transitional cells typically showed multiple components in their upstroke. Both our morphological and electrophysiological findings are compatible with the existence of a relatively high-resistance barrier between Purkinje and transitional cells and between transitional and ventricular muscle cells.
Differential effects of transforming growth factor-beta 1 and phorbol myristate acetate on cardiac fibroblasts. Regulation of fibrillar collagen mRNAs and expression of early transcription factors.
Authors: Eghbali M , Tomek R , Sukhatme V P , Woods C , Bhambi B
Published: June 2012

Cardiac fibroblasts are responsible for synthesis and deposition of fibrillar collagen types I and III. Transforming growth factor-beta 1 (TGF-beta 1) has been proved to increase collagen biosynthesis in various systems, both in vivo and in vitro. We have investigated the effect of TGF-beta 1 on collagen gene expression in cultured cardiac fibroblasts and have compared this effect with that of a mitogenic agent, phorbol myristate acetate (PMA). The regulation of collagen types I and III gene expression was examined by using cDNA probes to rat alpha 2 (I) and mouse alpha 1 (III) procollagens. Quiescent cultured cardiac fibroblasts from rabbit heart were treated with TGF-beta 1 (10-15 ng/ml) and PMA (200 ng/ml). After 24 hours of treatment with TGF-beta 1, the abundance of mRNA for pro-alpha 2 (I) and pro-alpha 1 (III) collagens was increased by 112% (p less than 0.001) and 97% (p = 0.05), respectively, in treated fibroblasts compared with untreated cells. However, PMA-treated cells showed an opposite response: a 42% (p = 0.01) decrease in mRNA levels for pro-alpha 2 (I) collagen was observed. Immunofluorescent staining of cardiac fibroblasts in culture with anti-type I collagen antibody showed that alterations in mRNA levels led to altered collagen synthesis: cellular collagen was relatively increased in TGF-beta 1-treated cells and significantly diminished in PMA-treated cells. The abundance of mRNA for pro-alpha 1 (III) collagen was not affected by PMA treatment.(ABSTRACT TRUNCATED AT 250 WORDS)
Subpopulations of rat vascular smooth muscle cells as discriminated by calcium release mechanisms from internal stores.
Authors: Shin W S , Toyo-oka T , Masuo M , Okai Y , Fujita H , Sugimoto T
Published: June 2012

Transsarcolemmal influx and release from the sarcoplasmic reticulum (SR) through specific Ca2+ channels are the two main pathways to elevate cytosolic Ca2+ (Ca2+i) in vascular smooth muscle cells (VSMCs). To elucidate intercellular distribution and function of the Ca2+ channel in SR in cultured VSMCs, we observed Ca2+i transients by digital two-dimensional imaging with a fluorescent Ca2+ indicator, fura-2, and found an alternative response to either caffeine or angiotensin II under the condition that selectively enabled Ca2+ release from SR. Caffeine (20 mM) increased the Ca2+i by 292 +/- 36% (mean +/- SEM) over the basal level in one third of the VSMC population (n = 19), while the remaining cells in the same observation field showed no or very weak response (110 +/- 4%). In contrast, after the treatment with caffeine plus ryanodine (30 microM), which inactivates the caffeine-sensitive channel, and with 1 mM Ca2+ chelator (EGTA) instead of Ca2+ in the incubation medium to block the CA2+ entry from outside, angiotensin II (10 nM) induced the Ca2+i elevation (287 +/- 26%) in previously caffeine-nonresponsive cells, although caffeine-responsive cells retained quiescence (112 +/- 2%). These responses did not differ when the order of the reagent application was reversed. These heterogeneities of VSMCs in the Ca2+i response to vasoactive substances indicate that VSMCs are functionally divided into subgroups with different Ca2+ channel predominance on SR, necessitating reevaluation of the previous studies obtained from multiple VSMCs.
Endothelin 1 enhances myofilament Ca2+ responsiveness in aequorin-loaded ferret myocardium.
Authors: Wang J X , Paik G , Morgan J P
Published: June 2012

The influence of endothelin 1 on intracellular Ca2+ transients and isometric contractions was investigated in ferret papillary muscles loaded with the Ca(2+)-regulated bioluminescent indicator aequorin. In concentrations of 3 x 10(-9) to 1 x 10(-7) M, endothelin produced dose-dependent increases in the amplitudes of both aequorin light signals (maximum, 31 +/- 12%) and developed tension (maximum, 64 +/- 13%). The peak aequorin light [( Ca2+]i)-peak tension curve generated by increasing endothelin concentrations was steeper and shifted to the left of the curve generated by varying [Ca2+]o; however, the maximum developed tension produced by endothelin did not exceed that produced by 6 mM [Ca2+]o. The effect of endothelin on the amplitude of the aequorin light signal was less than the effect of [Ca2+]o for similar levels of tension development. Moreover, 1 x 10(-7) M endothelin caused an upward shift in the peak aequorin light-peak tension curve generated by varying [Ca2+]o and increased the maximum twitch force by about 12%. The contractions were prolonged, whereas the time course of the Ca2+ transient was not changed in the presence of endothelin. When the function of the sarcoplasmic reticulum was inhibited by 6 microM ryanodine, 10(-7) M endothelin still increased the force generation without increasing the intracellular peak Ca2+, either during isometric twitches or during tetani.(ABSTRACT TRUNCATED AT 250 WORDS)
Evidence for developmental changes in sodium channel inactivation gating and sodium channel block by phenytoin in rat cardiac myocytes.
Authors: Xu Y Q , Pickoff A S , Clarkson C W
Published: June 2012

The voltage-dependent properties of the voltage-activated sodium channel were studied in neonatal (1-2-day-old) and adult rat ventricular cardiac myocytes using the whole-cell variation of the patch-clamp technique (16 degrees C, [Na]i = 15 mM, [Na]o = 25 mM). The voltage dependence of the sodium conductance-membrane potential relation was similar in both neonatal and adult myocytes except for a difference in slope; the adult sodium conductance-membrane potential relation was slightly more steep. Neonatal cells also differed from adult cells by demonstrating a more negative voltage midpoint of their sodium availability curve, a slower rate of recovery from inactivation at hyperpolarized potentials, and a greater extent of slow inactivation development compared with adult cells. Phenytoin (40 microM) reduced the sodium current in a tonic and use-dependent manner in both adult and neonatal myocytes. However, phenytoin (40 microM) produced significantly more tonic block at negative holding potentials (e.g., -140 mV) in neonatal myocytes (22 +/- 5% [mean +/- SEM], n = 14) than in adult myocytes (10 +/- 2%, n = 11) (p less than 0.05). The amplitudes of use-dependent block obtained during trains of 1-second pulses to -20 mV were also significantly greater in neonatal myocytes than in adult myocytes when the diastolic interval was varied over a range of 0.1-1.5 seconds (p less than 0.05). Definition of the time courses of block development at -20 mV indicated that phenytoin had a slightly higher affinity for inactivated sodium channels in neonatal cells. In addition, the time constant of recovery from use-dependent block by phenytoin was found to be significantly longer in neonatal cells than in adult cells at membrane potentials between -160 and -100 mV (p less than 0.001). The marked differences in phenytoin effect on cardiac sodium channels in neonatal versus adult rat cardiac myocytes suggest that there may be significant developmental changes in the sodium channel blocking effects of class I antiarrhythmic drugs in cardiac tissue.