bluuebunny/crossref_metadata_2025 huggingface dataset:
Stimulation of slow action potentials in guinea pig papillary muscle cells by intracellular injection of cAMP, Gpp(NH)p, and cholera toxin.
Authors: Li T , Sperelakis N
Published: June 2012

To test the hypothesis that intracellular cAMP has a regulatory role in cardiac slow channel function, intracellular pressure injections of cAMP and adenylate cyclase activators, Gpp(NH)p and cholera toxin, were carried out. Guinea pig papillary muscles were depolarized to about -45 mV by superfusion with 22 mM K+-Tyrode's solution to inactivate the fast Na+ channels. Induction of slow action potentials or enhancement of ongoing slow action potentials was observed in about 70% of all cells in which a successful intracellular injection of the testing compounds was obtained. The slow AP is highly dependent on slow inward current and is known to be enhanced by catecholamines. The effect of the injected cyclic nucleotides and related compounds occurred within 3 minutes after starting the injection, whereas superfusion with these compounds (dibutyryl cAMP was used in place of cAMP) required 10-30 minutes to show an effect. This difference is attributed to the intracellular injection of the compound. The effect on stimulating slow action potentials persisted (greater than 5 minutes) after termination of the application of either Gpp(NH)p or cholera toxin, indicating the long-lasting nature of their action. The effect of the cAMP injections decayed within 1 minute. Intracellular injection of 5'-AMP was without effect. These results support the view that a causal relationship exists between intracellular cAMP level and slow channel function. Phosphorylation of a protein constituent of the slow channel by a cAMP-dependent protein kinase may be involved.
Dynamic ventricular interaction in the conscious dog.
Authors: Olsen C O , Tyson G S , Maier G W , Spratt J A , Davis J W , Rankin J S
Published: June 2012

In nine conscious, chronically instrumented dogs, ultrasonic dimension transducers measured left ventricular anterior-posterior and septal-free wall minor axis and major axis diameters. Matched micromanometers measured right and left ventricular transmural and transeptal pressures. Ventricular pressures and volumes were varied by inflation of implanted vena caval and pulmonary artery occluders, and the functional significance of the two types of ventricular interaction, i.e., direct and series, was determined. The left ventricle was represented by a modified ellipsoidal geometry. Left ventricular stroke volume calculated from the dimension data correlated well with that measured directly from ascending aortic electromagnetic flow probes during all interventions (r greater than or equal to 0.96). Partial pulmonary artery occlusion significantly increased right ventricular diastolic and systolic pressures as compared to values obtained during control and venal caval occlusion. During pulmonary artery occlusion, latitudinal septal eccentricity was increased throughout the cardiac cycle compared to control and vena caval occlusion (P less than 0.05), indicating leftward interventricular septal shifting and significant alteration of left ventricular shape. The normalized diastolic pressure-volume curve was shifted to the left with pulmonary artery occlusion compared to control and indicated a decrease in left ventricular chamber compliance. However, when selected cardiac cycles with similar end-diastolic volumes from vena caval and pulmonary artery occlusions were compared, parameters of left ventricular systolic function (stroke volume, percent systolic shortening, peak aortic blood flow, peak left ventricular pressure, and its first derivative) remained relatively constant. These data suggest that mean myocardial fiber length is the major preload determinant of left ventricular systolic function independent of chamber pressure and shape, and that direct ventricular interaction mediated by interventricular septal shifting has minimal effects on systolic myocardial performance in this model. Thus, series ventricular interaction during acute imbalances in biventricular loading, where the output of the right ventricle determines the input of the left, seems to be far more important than direct interaction to the regulation of overall cardiac function.
Comparative studies of atrial and ventricular myosin from normal, thyrotoxic, and thyroidectomized rabbits.
Authors: Banerjee S K
Published: June 2012

Changes in enzymatic and structural properties of ventricular myosin in thyrotoxic rabbit hearts have been investigated extensively. However, there is little information regarding the effect of thyroid hormone on the atrial myosin. In this study, we have compared enzymatic and structural changes of ventricular and atrial myosin from euthyroid, hypothyroid, and hyperthyroid rabbits. In euthyroid rabbits, Ca++- and actin-activated ATPase activities of atrial myosin were 2-fold greater than those of the ventricular myosin. The Ca++- and actin-activated ATPase activities of atrial myosin from hypothyroid and hyperthyroid rabbits were identical with the values for atrial myosin from euthyroid rabbits. The same ATPase activities of ventricular myosin decreased in hypothyroid hearts but increased in hyperthyroid rabbits. The K+ (EDTA)-ATPase activities of all myosins were the same, irrespective of the thyroid status of the animal. Pyrophosphate-polyacrylamide gel electrophoresis patterns showed two isoenzymes (designated as A1 and A3) of atrial myosin in euthyroid hearts. The same electrophoretic patterns also showed in atrial myosin from hypothyroid and hyperthyroid hearts. The ventricular myosin from euthyroid hearts also exhibited two isoenzymes (designated as V1 and V3) but each with slower electrophoretic mobilities than the corresponding atrial myosin. In hypothyroid hearts, only V3 isoenzyme was seen, whereas, in hyperthyroid hearts, only V1 isoenzyme was seen. These results suggest that thyroid hormone controls ventricular myosin ATPase activity by controlling synthesis of a specific ventricular isoenzyme, whereas thyroid hormone does not affect atrial myosin ATPase, possibly due to its inability to control atrial myosin synthesis.
Mechanism of adenosine inhibition of catecholamine-induced responses in heart.
Authors: Dobson J G
Published: June 2012

The properties of adenosine inhibition of catecholamine-induced responses were investigated, using an isolated rat heart preparation. Perfusion of hearts with 0.1 microM isoproterenol increased myocardial cAMP content 2.8-fold, activation of cAMP-dependent protein kinase 4.4-fold, phosphorylase a formation 3.4-fold, left ventricular pressure 1.8-fold, rate of ventricular pressure development 2.1-fold, and rate of ventricular relaxation 2.2-fold within 1 minute. When perfused with the isoproterenol, 10 microM adenosine reduced the catecholamine-produced increase in cAMP, cAMP-dependent protein kinase, and phosphorylase by 30-40%, and the elevation in left ventricular pressure and rate of ventricular pressure development by 40-70% within 40 seconds. More than 2 minutes were required for the nucleoside to significantly reduce the isoproterenol-elicited increase in the rate of ventricular relaxation. Perfusion of adenosine alone at concentrations from 0.1 to 10 microM were without effect on the above parameters. Theophylline at 50 microM had no effect alone on the above parameters but blocked the inhibitory actions of adenosine on the isoproterenol-induced responses. In the presence of 15 mM Mg++ adenosine reduced by approximately 56% the 2-fold increase in myocardial membrane adenylate cyclase activity produced by 1 microM isoproterenol without affecting basal or fluoride-stimulated activity. Adenosine also reduced the isoproterenol-induced increase in enzyme activity assayed at 1-2 mM Mg++, a level that more closely approximates the intracellular activity of the ion. The results suggest that physiological concentrations of adenosine attenuate the catecholamine-induced increase in cAMP content, cAMP-dependent protein kinase activation, phosphorylase a formation, and contractile parameters in the working heart, via reducing the beta-adrenergic activation of adenylate cyclase.
Contractions of canine vascular smooth muscle cells caused by ouabain are due to release of norepinephrine from adrenergic nerve endings.
Authors: Aarhus L L , Shepherd J T , Tyce G M , Verbeuren T J , Vanhoutte P M
Published: June 2012

Experiments were performed to determine whether the contractions of isolated canine blood vessels caused by ouabain are due solely to the release of endogenous norepinephrine. The response of segments of splenic arteries and veins and strips of splenic capsules to ouabain were compared before and after surgical sympathectomy. Successful denervation was demonstrated by absence of a contractile response to electrical stimulation, supersensitivity to exogenous norepinephrine, an extremely low content of endogenous norepinephrine, reduced accumulation of 3H-norepinephrine, and inability of electrical stimulation and tyramine to augment the overflow of 3H-norepinephrine. Ouabain augmented the overflow of 3H-norepinephrine from control but not from denervated splenic capsule. It caused contraction of control but not of denervated splenic arteries, veins, and capsules. Studies were also conducted in the same tissues and in segments of mesenteric and femoral arteries and of circular and longitudinal segments of the portal mesenteric vein before and after chemical sympathectomy with 6-hydroxydopamine. In these tissues, the contractile responses to electrical stimulation but not exogenous norepinephrine and prostaglandin F2 alpha were abolished. In the control tissues, ouabain caused strong contractions, whereas, in the denervated tissues, only a weak or no response to the glycoside occurred. The study demonstrates that, in isolated canine blood vessels, ouabain causes contraction of smooth muscle cells by virtue of its ability to release norepinephrine from the sympathetic nerves.
Enrichment, solubilization, and partial characterization of digitonin-solubilized muscarinic receptors derived from canine ventricular myocardium.
Authors: Manalan A S , Werth D K , Jones L R , Watanabe A M
Published: June 2012

The subcellular distribution of cardiac muscarinic receptors was defined in canine ventricular myocardium, and receptors were solubilized from subcellular fractions enriched in muscarinic receptor content. The subcellular location of muscarinic receptors in cardiac tissue was determined by measurement of the distribution of [3H](+/-)quinuclidinyl benzilate-binding activity in particulate fractions isolated from canine ventricular myocardium. Based upon excellent correlation between [3H](+/-)quinuclidinyl benzilate binding and activity of the sarcolemmal Na+,K+-ATPase throughout the subcellular fractions, muscarinic receptors appeared to be localized to sarcolemma in canine ventricular myocardium. Therefore, membrane fractions enriched in sarcolemma were used as a source of cardiac muscarinic receptors for solubilization. Treatment of membrane vesicle fractions with digitonin (0.6%) resulted in solubilization of [3H](+/-)quinuclidinyl benzilate-binding activity with an extraction yield of 25-35%. Criteria of pharmacological specificity and stereospecificity established the identity of the solubilized binding activity of muscarinic receptors. Solubilization of muscarinic receptors was documented by demonstration of hydrodynamic behavior consistent with molecularly dispersed material. Upon glycerol gradient centrifugation, digitonin-solubilized muscarinic receptors from cardiac tissue sedimented with an apparent sedimentation coefficient of 9S. Pharmacological characterization of the digitonin-solubilized receptors revealed 8- to 39-fold reductions in affinities for muscarinic antagonists compared to the affinities exhibited by receptors in the membrane-bound state. Substantially greater reductions in agonist affinities (reduction of at least 700-fold for all agonists studied) suggested selective loss of ability of the digitonin-solubilized receptors to exhibit high affinity agonist interactions. In contrast to membrane-bound receptors, digitonin-solubilized receptors also demonstrated a loss of guanine nucleotide regulation, as well as steep agonist:radioligand competition curves with slope factors of 1.0, suggesting a homogeneous population of agonist-binding sites. Interpreted within the context of a model of state interconversion for membrane-bound receptors, the results suggested that either muscarinic receptors of a single state were selectively solubilized, or that solubilization induced conversion of all receptors to a single low affinity state, possibly by removal of constituents necessary for assumption of a high affinity agonist conformation.
The influence of molecular form of local anesthetic-type antiarrhythmic agents on reduction of the maximum upstroke velocity of canine cardiac Purkinje fibers.
Authors: Gintant G A , Hoffman B F , Naylor R E
Published: June 2012

We studied the local anesthetic effects of the quaternary lidocaine analogues QX-314, QX-572, and QX-222, the tertiary amine lidocaine, its analogues tocainide, 6603, 6211, and the neutral local anesthetic benzocaine to determine if molecular charge of antiarrhythmic agents influences their local anesthetic effects on heart fibers. We used standard microelectrode techniques and canine cardiac Purkinje fibers to compare the effects of stimulation rate, drug concentration, and K+-induced changes in resting membrane potential on the reduction of fast inward sodium current using the maximum rate of rise of the action potential upstroke, Vmax, as an index of changes in peak sodium current. Use-dependent block, defined as a modulation of the reduction in Vmax by local anesthetics due to changes in the stimulation rate, was observed with the permanently charged analogues and was most prominent for agents existing predominantly in the charged form, but was absent for the neutral local anesthetic benzocaine. The development of use-dependent block during rapid stimulation preceded by prolonged periods of quiescence was an exponential process which became more rapid with increasing drug concentration. Recovery from use-dependent block during quiescence was an exponential process that was not influenced by similar drug concentration changes. All local anesthetics caused tonic block, defined as a drug-induced reduction of Vmax from control that attained a constant value at slow stimulation rates (cycle length range 15 seconds to 2 minutes) and was not changed by prolonged (up to 8 minutes) periods of quiescence. These findings suggest that the charged form of lidocaine and its analogues is responsible for use-dependent block of cardiac sodium channels.
Glomerular ultrafiltration coefficient after ischemic renal injury in dogs.
Authors: Savin V J , Patak R V , Marr G , Hermreck A S , Ridge S M , Lake K
Published: June 2012

Micropuncture studies of acute renal failure after ischemic renal injury suggest that glomerular ultrafiltration coefficient may remain normal in the period immediately after ischemia and decline significantly during the following 18-24 hours. The present series of in vitro experiments was designed to evaluate glomerular ultrafiltration coefficient and glomerular oncometric and rheological properties in ischemic acute renal failure in dogs. To obtain glomeruli prior to ischemia, a right nephrectomy was performed and glomeruli were isolated for studies of filtration and cell and extracellular spaces. The left renal pedicle then was occluded for 90 minutes; glomeruli isolated from biopsies of this kidney were studied at intervals up to 48 hours after ischemia. Glomeruli were isolated by sieving renal cortical fragments, and filtration was induced by an oncotic gradient. The glomerular ultrafiltration coefficient remained near control levels for the first hour after ischemia, but declined significantly at 24 and 48 hours. Specifically, glomerular ultrafiltration coefficient of glomeruli isolated from normal kidneys was 16.5 +/- 0.9 nl/min per mm Hg (n = 15). Immediately following ischemia, glomerular ultrafiltration coefficient remained essentially unchanged (15.9 +/- 1.1 nl/min per mm Hg, n = 4). At 1 hour, there was a small decrease in glomerular ultrafiltration coefficient (14.4 +/- 1.3 nl/min per mm Hg, n = 4). At 24 hours, glomerular ultrafiltration coefficient was significantly decreased (9.8 +/- 0.5 nl/min per mm Hg, n = 9, P less than 0.01) and remained at that level at 48 hours (9.5 +/- 0.5 nl/min per mm Hg, n = 8, P less than 0.001). In experimental glomeruli, the oncometric response was diminished and erythrocyte movement along glomerular capillaries was impaired. Total water and inulin spaces were measured in glomeruli from control and 48-hour postischemic periods, and glomerular morphology was studied by transmission and scanning electron microscopy at the same time.(ABSTRACT TRUNCATED AT 250 WORDS)
Effects of cations, phospholipases, and neuraminidase on calcium binding to "gas-dissected" membranes from cultured cardiac cells.
Authors: Langer G A , Nudd L M
Published: June 2012

Sarcolemmal membranes prepared by "gas dissection" from monolayers of cultured neonatal rat heart cells were studied with respect to their ability to bind calcium. Lanthanum displacement of calcium was 168 +/- 7 nmol/mg sarcolammel protein. This represents 3.21 mmol Ca/kg dry weight original cells on the basis of the measured membrane protein: dry cell weight ratio of 19.1 g/kg. Lanthanum-displaceable calcium from whole cells was essentially equal (3.32 mmol/kg dry weight), which indicates that all calcium displaceable from whole cells by lanthanum is localized to sarcolemmal sites. The potency of a series of divalent cations for calcium displacement from the sarcolemma was according to similarity of their crystal radii to that of calcium (cadmium greater than manganese greater than magnesium). This order was the same for the cations' ability to displace calcium from whole cells and for their ability to uncouple excitation from contraction in neonatal papillary muscle. The membranes were treated with four enzymes: phospholipase A2, phospholipase C, phopholipase D, and neuraminidase. Phospholipase A2 and phospholipase D produced significantly increased calcium-binding. The increased binding secondary to phospholipase A2 treatment was eliminated by an albumin wash which was indicative of binding to the fatty acid product of hydrolysis. The increase after phospholipase D treatment can be attributed to an increase in phosphatidate, with attendant increase in net anionic charge on the membrane.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of coronary artery pressure on transmural distribution of adrenergic coronary vasoconstriction in the dog.
Authors: Buffington C W , Feigl E O
Published: June 2012

The transmural distribution of alpha-receptor coronary vasoconstriction was studied in 14 closed-chest, morphine- and chloralose-anesthesized dogs. The alpha-receptor-blocking agent, phenoxybenzamine (0.25 mg/kg), was infused into either the anterior or circumflex coronary artery while collection of coronary sinus blood minimized recirculation. The left main coronary artery was cannulated and perfused at constant pressure. Myocardial lactate extraction and blood flow (9 micron radioactive microspheres) were measured during adrenergic activation with intracoronary norepinephrine (2 micrograms/min) at coronary artery pressures of 100, 70, 50, and 38 mm Hg. Flow was 15-25% less in the control region (alpha-receptors intact) than in the alpha-receptor-blocked region, in all layers of the left ventricular wall, at coronary pressures of 100 and 70 mm Hg. When coronary pressure was 50 mm Hg, lactate production resulted (-4% extraction) and significant alpha-receptor vasoconstriction was observed in the outer layer, but was marginal (P = 0.043) in the inner layer, of the left ventricle. Flows were not different in control and alpha-receptor-blocked regions at a coronary pressure of 38 mm Hg (lactate extraction -49%). These data indicate a uniform transmural alpha-receptor vasoconstriction at normal coronary artery pressures that diminished as the heart was progressively underperfused.
Transcapillary water and protein flux in the canine intestine with acute and chronic extrahepatic portal hypertension.
Authors: Witte C L , Myers J F , Witte M H , Katz M A
Published: June 2012

Intestinal transcapillary water and total protein flux were determined in dogs with chronic extrahepatic portal hypertension after construction of an aortic-portal shunt combined with hilar portal vein constriction and compared to acute portal vein constriction. Measurements were made of thoracic duct lymph flow, portal venous pressure, and total protein concentration in plasma, thoracic duct lymph, intestinal and liver lymph. From these data and calculations based on the dual visceral origin of thoracic duct lymph from liver and intestine, intestinal transcapillary water flux in chronic extrahepatic portal hypertension (portal venous pressure = 21.4 +/- 2 mm Hg; mean +/- SEM), increased 5-fold (93 +/- 12 from 17 +/- 4 microliters/min/kg, P less than 0.001), while intestinal total protein flux expressed as protein clearance (intestinal transcapillary water flux X intestinal lymph/plasma total protein concentration) was unchanged (13 +/- 3 from 10 +/- 2 microliters/min per kg; P greater than 0.4), a finding supported by unaltered whole body plasma albumin "leak rate" (83 +/- 16 from 80 +/- 2 microliters/min per kg; P greater than 0.9). In acute portal vein constriction (portal venous pressure = 26 +/- 1 mm Hg) intestinal transcapillary water flux was similarly increased (58 +/- 16 from 9 +/- 2; P less than 0.014) but intestinal total protein flux was increased 3-fold (16 +/- 4 from 5 +/- 2; P less than 0.032). Calculated permeability surface area product and protein reflection coefficient (cross-point method) increased similarly in both preparations. In accord with earlier findings in patients with hepatic cirrhosis, chronic elevation in portal pressure increased intestinal transcapillary water flux but not total protein flux.
Phasic release of adenosine during steady state metabolic stimulation in the isolated guinea pig heart.
Authors: DeWitt D F , Wangler R D , Thompson C I , Sparks H V
Published: June 2012

If adenosine is the major factor responsible for myocardial metabolic vasodilation, its release should be sustained as long as oxygen consumption and coronary flow are augmented. To see if adenosine meets this criterion, we examined the time course of its release during norepinephrine infusion in isolated, non-working guinea pig hearts (n = 8). During an 11-minute infusion period (steady state perfusate concentration = 6 X 10(-8) M), the coronary effluent was collected over 30-second intervals for measurements of coronary flow (ml/min per g), and adenosine and inosine release (pmol/min per g). Myocardial oxygen consumption (MVO2 = microliter O2/min per g) was measured at 1, 4, 6.5, and 11 minutes. Control values of coronary flow, myocardial oxygen consumption, and adenosine and inosine release were 7.5 +/- 0.4, 85 +/- 5, 22 +/- 5, and 431 +/- 39, respectively. During norepinephrine infusion, coronary flow, myocardial oxygen consumption, and adenosine release attained maximal levels within one minute (inosine within 2 minutes). These values were 10.6 +/- 0.4, 125 +/- 9, 849 +/- 110, and 2595 +/- 581, respectively. Thereafter, coronary flow and myocardial oxygen consumption values were sustained. In contrast, adenosine and inosine release significantly declined to nadirs by 9.5 minutes. Thereafter, steady state levels were maintained at 117 +/- 24 and 960 +/- 294, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
Influence of polymyxin B, a probe for anionic phospholipids, on calcium binding and calcium and potassium fluxes of cultured cardiac cells.
Authors: Burt J M , Duenas C J , Langer G A
Published: June 2012

Polymyxin B, an amphiphilic, cationic peptidolipid, which is thought to bind to anionic phospholipids in cell membranes, is shown to interact with the cellular calcium of cultured neonatal rat myocardial cells in a dose-dependent, partially reversible manner. At concentrations of less than or equal to 0.1 mM, it has two distinct effects. First, it results in displacement of 1.4 +/- 0.3 mmol Ca/kg dry weight, which is equivalent to 18.1 +/- 3.4% of the total exchangeable cellular calcium. Total calcium displaced by polymyxin B and a nonspecific cationic probe, lanthanum, at its maximal displacing concentration (1 mM), was 5.9 +/- 1.3 mmol/kg dry weight. Thus, the total displaceable calcium represented 76.3 +/- 2.5% of the total exchangeable calcium. Second, polymyxin B (less than or equal to 0.1 mM) causes a reduction in net uptake of calcium, and slows the efflux of both calcium and potassium. Concentrations of polymyxin B higher than 0.1 mM result in an initial displacement of calcium, followed by an irreversible and sustained period of enhanced net calcium uptake. Efflux of calcium is slowed at the higher polymyxin B concentrations, whereas efflux of potassium is enhanced. Cellular contractile activity and electrical activity are irreversibly altered only by the higher concentrations. The results suggest that polymyxin B is a useful probe for the role of membrane phospholipids in control of ion binding and fluxes.
Mechanisms of escape from desmopressin in the rat.
Authors: Gross P A , Kim J K , Anderson R J
Published: June 2012

The mechanism(s) of renal escape from the hydro-osmotic effect of vasopressin is unknown. We therefore studied escape in conscious, unrestrained rats receiving continuous intravascular infusions of 1-deamino-8-arginine-vasopressin (desmopressin) and hypotonic fluid over 5 days. Escape from desmopressin started 8 hours after exposure and was characterized by a progressive increase in urine flow and decreases in urine osmolality and free water reabsorption. When positive water balance was prevented by matching the rate of infusion of hypotonic fluid to urine flow while maintaining the dose of desmopressin constant, escape did not occur. This suggested that water retention, rather than chronic exposure to desmopressin, mediated the escape. To elucidate the mechanism whereby water retention induces escape from desmopressin, urinary prostaglandin E2 excretion was measured and found to be increased concomitant with the onset of escape. Prevention of this increase in urinary prostaglandin E2 excretion with indomethacin resulted in additional water retention and a delay in the onset of escape. During the maintenance of escape, after significant water retention occurred, increases in mean arterial pressure, renal blood flow, and glomerular filtration rate were observed. Renal interstitial solute concentration remained constant through escape. Basal and vasopressin-stimulated collecting tubular and thick ascending limb adenylate cyclase did not differ when control and escape animals were compared. These results suggest that enhanced renal synthesis of prostaglandin E2 facilitates the early phase of escape; later, water retention results in plasma volume expansion with increases in cardiac index, arterial pressure, renal blood flow, and glomerular filtration rate. These systemic and renal hemodynamic alterations may be important in maintaining escape from desmopressin.
Effects of endothelial denudation and cholesterol feeding on in vivo transport of albumin, glucose, and water across rabbit carotid artery.
Authors: Chobanian A V , Menzoian J O , Shipman J , Heath K , Haudenschild C C
Published: June 2012

An in vivo system for studying arterial transport was developed which utilized the rabbit carotid artery perfused in vivo with Dulbecco's modified Eagle's medium containing 125I-labeled albumin, [3H]-3-methyl-d-glucose, or tritiated water. The appearance of labeled materials in jugular venous blood was measured serially over 4 hours. Vascular integrity was assessed by scanning electron and transmission microscopy. Maintenance of endothelial integrity appeared dependent on perfusion with nutrient tissue culture medium, use of papaverine to inhibit arterial spasm, and circulation of the medium under pressure. Acute endothelial denudation with a balloon catheter induced an approximate 10-fold increase in plasma concentration of labeled albumin and a 3-fold rise in plasma [3H]-3-methyl-d-glucose activity, compared with results in animals with intact endothelium. Increased appearance of tritiated water in venous blood was also observed in the rabbits with denuded endothelium, although the relative rise was less than that with albumin or glucose. Feeding rabbits a diet containing 1.5% cholesterol for periods of 16-28 weeks produced approximately 10-fold increases in plasma concentration of 125I-labeled albumin after arterial perfusion to levels comparable to those present in chow-fed rabbits with experimental endothelial denudation. The increases in albumin transport with cholesterol feeding occurred even though a relatively small fraction of the intimal surface was involved with lesions. The results suggest that the arterial endothelium provides a relative barrier to albumin and, to a lesser extent, glucose and water. The findings also suggest that cholesterol feeding markedly increases arterial permeability to albumin, to a degree that is disproportionately greater than the extent of atherosclerotic involvement of the intimal surface.
Unitary sodium channels in isolated cardiac myocytes of rabbit.
Authors: Grant A O , Starmer C F , Strauss H C
Published: June 2012

Transmembrane ionic movements are thought to occur through special membrane areas or channels. Until recently, it has not been possible to study the properties of individual ionic channels, directly. We have used the extracellular patch clamp technique to resolve unitary sodium channels in enzyme-dissociated rabbit ventricular myocytes. Depolarizing voltage clamp steps elicited rectangular inward current fluctuations representing open-closed transition of the channels. Probability of channel opening increased with depolarization. Single channel current amplitude ranged from 0.6 to 1.9 pA. Channel open time increased with depolarization. Sodium channels could be distinguished from calcium channels by their insensitivity to cadmium and inactivation voltage range. First-event latency histograms suggest multiple-closed states. The patch clamp technique can be readily applied to the study of sodium channels in adult cardiac myocytes.
Mechanism of 5-HT contraction in isolated bovine ventricular coronary arteries. Evidence for transient receptor-operated calcium influx channels.
Authors: Ratz P H , Flaim S F
Published: June 2012

The effect of serotonin on isometric tension and transmembrane calcium influx was investigated in rings cut from branches of male bovine circumflex and left anterior descending coronary arteries. Responses were compared to those produced by potassium chloride, and to the serotonin contraction produced in rabbit thoracic aorta. Serotonin in bovine ventricular coronary arteries produced a strong, transient contraction, even at a maximum concentration. Contraction did not decline because of serotonin degradation in the bathing medium. The ability of serotonin to contract bovine ventricular coronary arteries was largely preserved when rings were exposed to a calcium-free medium. When calcium was replaced in the medium, both tension (T) and calcium influx (C, 45Ca) were increased above control only transiently by serotonin (3 minutes post-serotonin: T = 49.0 +/- 13.3 mg/mg, C = 27.33 +/- 1.8 mumol/kg, compared with control T = -4.8 +/- 1.5, C = 19.7 +/- 1.4; 30 minutes post-serotonin: T = -17.3 +/- 2.1, C = 19.3 +/- 1.1, compared with control T = -19.6 +/- 4.1, C = 18.1 +/- 1.4). Potassium chloride-stimulated increases in tension and calcium influx in bovine ventricular coronary arteries and a maximum serotonin contraction in rabbit thoracic aorta were not transient, but were sustained 30 minutes via a mechanism that appeared to be dependent on the influx of extracellular calcium. We suggest that the transient nature of the serotonin contraction in bovine ventricular coronary arteries was the result of a time-dependent decline in both calcium release from intracellular stores and calcium influx through serotonin receptor-operated calcium channels.(ABSTRACT TRUNCATED AT 250 WORDS)
Ultrastructure of isolated sarcolemma from dog and rabbit myocardium. Comparison to intact tissue.
Authors: Frank J S , Philipson K D , Beydler S
Published: June 2012

We compared the morphology of cardiac sarcolemmal membranes isolated from dog and rabbit hearts with the sarcolemma in intact cells, using freeze-fracture and thin-section electron microscopy. In addition, we estimated the sidedness of the isolated sarcolemma based on its freeze-fracture morphology and biochemical determinations of sialic acid content and Na,K-ATPase activity. The bilayer in isolated membranes is similar, in its morphology, to intact membrane. The isolated sarcolemmal vesicles have the same density of intramembrane particles per micron2 as the intact sarcolemma (approximately 2800/micron2). The particle counts in isolated sarcolemma were very homogeneous, with the peak in particle density curve the same as found for intact cells. In the intact myocardium, both sarcolemmal and transverse tubular membranes have the same density of intramembrane particles. Thin-section morphology of the isolated sarcolemma shows an intact surface coat, whereas portions of the external lamina are absent. Both the biochemical and morphological data indicate that there is a substantial fraction of inside-out and right side-out vesicles in this preparation. Considering the approximations inherent in both morphological and biochemical approaches, we find the qualitative agreement of the estimations of vesicle orientation noteworthy.
Rabbit papillary muscle myosin isozymes and the velocity of muscle shortening.
Authors: Pagani E D , Julian F J
Published: June 2012

Rabbits, ages 4-24 weeks, were injected with saline or thyroxine (150 micrograms/kg) for 7 days, and force-velocity curves were generated using papillary muscles from these hearts by a method described previously. In addition, the structure and relative amounts of myosin isozymes from papillary muscles and from 3- to 5-mg segments of the left and right ventricular free wall were analyzed by polyacrylamide gel electrophoresis under native and denatured conditions. We found that rabbit papillary muscles may contain up to three isozymic forms of myosin (V1, V2, and V3) and that their relative amounts change with age of the rabbit and with thyroxine treatment. There were no differences between papillary muscles and ventricular free wall in the molecular weight of light chain1 (27,000) and light chain2 (21,500) of heavy chain alpha or in the peptide map of heavy chain alpha nor were there any differences between papillary muscles and the ventricular free wall in the molecular weight of light chain1 (27,000) and light chain2 (21,500) of heavy chain beta or in the peptide map of heavy chain beta. However, the relative amounts of myosin isozymes in the ventricular free walls and papillary muscles may not be identical within the same heart. Analysis of the force-velocity curves indicated that the speed of papillary muscle shortening is correlated with the relative amount of V1 myosin present in each papillary muscle. Papillary muscles that contain 100% V1 myosin shorten, under zero load, approximately six times faster than papillary muscles that contain 100% V3 myosin. Our results indicate that changes in the relative amounts of myosin isozymes are responsible, at least in part, for sustained alterations in the speed of papillary muscle shortening.
The time course of action potential repolarization affects delayed afterdepolarization amplitude in atrial fibers of the canine coronary sinus.
Authors: Henning B , Wit A L
Published: June 2012

The effects of changing the time course of action potential repolarization on the amplitude and coupling interval of delayed afterdepolarizations were studied in small preparations of coronary sinus atrial fibers exposed to catecholamines. Repolarization was accelerated or retarded by current pulses passed through an intracellular microelectrode in the depolarizing or repolarizing direction. Acceleration of repolarization decreased the amplitude of delayed afterdepolarizations, prolonged their coupling interval to the action potential upstroke, and prevented triggered activity. Prolonging the time for repolarization increased afterdepolarization amplitude, shortened the coupling interval, and caused triggered activity. The afterdepolarization amplitude and coupling interval had a linear relationship to the duration of the action potential plateau. In some preparations, the action potential plateau increased spontaneously at stimulation rates that caused afterdepolarization amplitude to increase and triggering to occur, and this may have contributed to the occurrence of triggering. The effects of action potential repolarization on delayed afterdepolarizations suggest that pharmacological agents such as antiarrhythmic drugs which alter action potential duration should influence afterdepolarizations. Drugs which shorten action potential duration might prevent triggered activity from occurring, whereas drugs which prolong duration might cause triggering.
Ejection timing as a major determinant of left ventricular relaxation rate in isolated perfused canine heart.
Authors: Hori M , Inoue M , Kitakaze M , Tsujioka K , Ishida Y , Fukunami M , Nakajima S , Kitabatake A , Abe H
Published: June 2012

In the present study, we attempted to test the hypothesis that ejection timing rather than peak left ventricular pressure is a primary determinant of ventricular relaxation rate. In cross-circulated isolated canine hearts instantaneous left ventricular volume was controlled by a servo-pump system. To eliminate the effects of end-systolic and end-diastolic volumes and ejection velocity on left ventricular relaxation rate, these parameters were clamped, and only the ejection timing (onset and end of ejection) was altered, keeping the duration of ejection unchanged. Left ventricular relaxation rate was assessed by time constants of left ventricular pressure decline during the isovolumic relaxation phase calculated by both a semilogarithmic method, assuming that the asymptote is zero, and a best exponential fitting method. In 25 runs, a pair of contractions with ejection timings which differed by 53.1 +/- 2.1 (SE) msec were imposed, while end-systolic and end-diastolic left ventricular volumes and ejection duration were unchanged. All pairs of contractions demonstrated early ejection resulted in significantly (P less than 0.001) slowed relaxation as indicated by a prolongation of the time constants of isovolumic left ventricular pressure decay (delta 4.2 +/- 0.7, sec and delta 15.4 +/- 2.1 msec by semilogarithmic plot and the best exponential fit respectively), although peak left ventricular pressures (104.6 +/- 2.4 mm Hg) were even lower than those (116.6 +/- 2.8 mm Hg) in contractions with later ejection timing. Furthermore, in seven experiments, the heart was allowed to eject at five different timings; onset and end of ejection were progressively delayed in steps of 20 or 30 msec.(ABSTRACT TRUNCATED AT 250 WORDS)
Interpretation and physiological significance of diastolic coronary artery pressure-flow relationships in the canine coronary bed.
Authors: Dole W P , Alexander G M , Campbell A B , Hixson E L , Bishop V S
Published: June 2012

We analyzed the relationship between diastolic coronary artery pressure and flow in the canine coronary bed, using an electrical analog model of the coronary circulation based on the theory of critical closure. The model contains a voltage-dependent nonlinear resistance and capacitance. The behavior of the resistive element was described using experimental diastolic pressure-flow curves obtained in the absence of compliance effects. Compliance free zero flow pressure intercepts (Pf0) exceeded coronary venous pressure (Pv) by 2- to 5-fold and were related to initial diastolic coronary artery pressure Pa(0) and flow F(0), and Pv by: Pf0 = 14.3 [(Pa(0) - Pv)/F(0)] + Pv + 4.0 (r = 0.93). When coronary artery pressure was suddenly lowered to values less than or equal to the compliance-free Pf0, diastolic flow abruptly decreased and, after a transient reversal, remained at zero for up to 8 seconds. In the model, zero flow pressure represents critical closing pressure and the resistance regulating flow is the difference between coronary artery and venous pressure divided by flow. Theoretically predicted pressure-flow curves were in good agreement with existing experimental data, including the effects of elevating coronary venous pressure on zero flow pressure. Differences between compliance-free pressure-flow curves and those obtained with pressure gradually decreasing were explained by a coronary arterial compliance whose magnitude varies inversely with pressure and is dependent on vasomotor tone. In conclusion, the results of this study demonstrate the existence of a diastolic pressure gradient across the canine coronary bed at zero flow which is dependent on coronary vasomotor tone. A theoretical model of the coronary circulation based on the concept of critical closure describes the observed relationship between diastolic coronary artery pressure and flow during various experimental conditions.
The isolated sinoatrial node cell in primary culture from the newborn rat.
Authors: Marvin W J , Chittick V L , Rosenthal J K , Sandra A , Atkins D L , Hermsmeyer K
Published: June 2012

We prepared primary cell cultures of the sinus node region from newborn rat hearts. Sinoatrial node cells were easily distinguished from the other cardiac muscle cells and nonmuscle cells in culture by size, configuration, and rapid, attenuated spontaneous contractions (185.0 +/- 8/min, mean +/- SEM). The spontaneously contracting sinoatrial node cells were extremely sensitive to acetylcholine and norepinephrine, responding to concentrations at least 1000-fold less than other cardiac muscle cells. These same sinoatrial node cells in culture were fixed and precisely relocated by either subsequent scanning or transmission electron microscopy. The ultrastructural features of these sinoatrial node cells in culture were similar to those observed in the cells of intact sinus node sections from the source hearts. This study is the first to present single, spontaneously active, neonatal sinoatrial node cells maintained in vitro with morphological and functional properties desirable for physiological investigations.
Evidence for the presence of calsequestrin in both peripheral and interior regions of sheep Purkinje fibers.
Authors: Jorgensen A O , McLeod A G , Campbell K P , Denney G H
Published: June 2012

Localization of calsequestrin in sheep Purkinje fibers was determined by indirect immunofluorescence labeling of cryostat sections of sheep myocardium from the intraventricular wall. The results presented show that calsequestrin is present in discrete foci at the peripheral, as well as the interior regions of the cytoplasm. Since Purkinje fibers lack transverse tubules, the presence of calsequestrin at specific foci in the interior regions of the cytoplasm in these cells suggests that calsequestrin is localized in the lumen of peripheral junctional sarcoplasmic reticulum, as well as in the lumen of corbular sarcoplasmic reticulum present in the I band region of the myofibrils. Assuming that the function of calsequestrin is to sequester calcium into the lumen of the sarcoplasmic reticulum, these results imply that two structurally different regions of the sarcoplasmic reticulum function as calcium storage sites in mammalian Purkinje fibers and raises the possibility that calcium storage and/or release from these two sites might be regulated differently.
Phasic vascular sodium pump changes in deoxycorticosterone-hypertensive rats.
Authors: Songu-Mize E , Bealer S L , Caldwell R W
Published: June 2012

We determined the sodium pump activity, measured as ouabain-sensitive 86Rb+ uptake, in the tail arteries of rats treated with deoxycorticosterone and sodium chloride for 6, 9, 14, 28, and 50 days. Systolic blood pressures, plasma sodium, potassium, and creatinine concentrations were measured, and the body weights were recorded. Vascular sodium pump activity was suppressed (by 27%) at the 6th day of deoxycorticosterone and sodium chloride treatment, a prehypertensive state. By the 9th day, blood pressure of deoxycorticosterone-treated and sodium chloride rats had increased, but sodium pump activity was not different from that of control animals. However, increases in sodium pump activity were noted after 14 and 28 days of deoxycorticosterone and sodium chloride treatment (18 and 21%, respectively). By 28 days, a fully developed hypertension was noted. At 50 days, rats displayed lower vascular sodium pump activity (by 23%) than the controls. These rats, although hypertensive, had significantly lower systolic blood pressures than the rats treated for 28 days. They had high plasma creatinine levels, low potassium and sodium concentrations, and low body weights compared to the controls, suggesting the presence of a malignant state. Our data indicate that there are time-related changes in the vascular sodium pump activity with this type of hypertension.
Regional end-systolic pressure-length relationships using a volume-loading technique in the intact pig heart.
Authors: Miller W P , Liedtke A J , Nellis S H
Published: June 2012

The purpose of this study was to characterize left ventricular systolic elastances as derived from pressure-segment length and pressure-diameter relationships, and to compare the resulting regional and global elastances to known changes in inotropy. Left ventricular pressure-segment length and pressure-diameter were varied in a series of consecutive beats by means of a volume-loading technique, and both regional and global relationships at 20-msec intervals throughout systole were found to be nonlinear and to exhibit hysteresis. In eight animals, regional hysteresis was present after vagotomy, propranolol (1.0 mg/kg), and atropine (0.1 mg/kg), and was present no matter whether hearts were loaded by volume (45-60 ml/sec) or by pressure (partial aortic occlusion) over a similar range of left ventricular systolic pressures. Elastance was linearly approximated by the slope of the major axis of the hysteresis loops. In each instance, elastance increased to a maximum and then decreased, thus defining end-systole. In seven animals, maximum elastance-length and -diameter were compared before and after treatments with dobutamine (5-13 micrograms/kg per min) and propranolol (6-51 micrograms/kg per min), or after induction of global ischemia. Dobutamine increased maximum elastance-diameter by 37% (P less than 0.01) and maximum elastance-length by 159% (P less than 0.05). Propranolol decreased maximum elastance-diameter by 27% (P less than 0.05) and maximum elastance-length by 6% (P = NS). Global ischemia (50% reduction in coronary flow) did not significantly change either maximum elastance-diameter or -length. However, with ischemia, the diameter intercept of maximum elastance-diameter increased by 24% (P less than 0.025), and the time to maximum elastance-length decreased by 33% (P less than 0.01). Comparing all interventions, the percent changes in maximum elastance-length and -diameter related directly but with a low correlation coefficient (r = 0.49). These differences in regional and global elastance suggest a complex relationship between regional and global myocardial mechanics, and may not necessarily reflect specific changes in contractility.