Galpha(i2) but not Galpha(i3) is required for muscarinic inhibition of contractility and calcium currents in adult cardiomyocytes

Parasympathetic stimulation of the heart acts through M(2)-muscarinic acetylcholine receptors to regulate ion channel activity and subsequent inotropic status. Although muscarinic signal transduction is mediated via pertussis toxin-sensitive G proteins Galpha(i/o), the specific signal transduction requirements of Galpha(i2) and Galpha(i3) in mediating muscarinic regulated L-type calcium currents (I(Ca, L)), intracellular calcium, and cell contractility remain to be determined. Adult ventricular myocytes were isolated from Galpha(i2)-null mice, Galpha(i3)-null mice, and their wild-type littermates. Cell shortening, intracellular calcium levels, and I(Ca, L) were all measured in response to isoproterenol, a beta-adrenergic receptor agonist, and carbachol, a cholinergic receptor agonist. With isoproterenol stimulation, myocytes from all groups demonstrated a marked increase in calcium currents, correlating with augmented intracellular calcium transient amplitude and cell shortening. Carbachol significantly attenuated the isoproterenol response in wild-type and Galpha(i3)-null cells but had no effect in Galpha(i2)-null cells. This study demonstrates that Galpha(i2), but not Galpha(i3), is required for muscarinic inhibition of the beta-adrenergic response in adult murine ventricular myocytes.

Altered beta-adrenergic signal transduction in nonfailing hypertrophied myocytes from Dahl salt-sensitive rats

Desensitization of the beta-adrenergic receptor (beta-AR) response is well documented in hypertrophied hearts. We investigated whether beta-AR desensitization is also present at the cellular level in hypertrophied myocardium, as well as the physiological role of inhibitory G (G(i)) proteins and the L-type Ca(2+) channel in mediating beta-AR desensitization. Left ventricular (LV) myocytes were isolated from hypertrophied hearts of hypertensive Dahl salt-sensitive (DS) rats and nonhypertrophied hearts of normotensive salt-resistant (DR) rats. Cells were paced at a rate of 300 beats/min at 37 degrees C, and myocyte contractility and intracellular Ca(2+) concentration ([Ca(2+)](i)) were simultaneously measured. In response to increasing concentrations of isoproterenol, DR myocytes displayed a dose-dependent augmentation of cell shortening and the [Ca(2+)](i) transient amplitude, whereas hypertrophied DS myocytes had a blunted response of both cell shortening and the [Ca(2+)](i) transient amplitude. Interestingly, inhibition of G(i) proteins did not restore beta-AR desensitization in DS myocytes. The responses to increases in extracellular Ca(2+) and an L-type Ca(2+) channel agonist were also similar in both DS and DR myocytes. Isoproterenol-stimulated adenylyl cyclase activity, however, was blunted in hypertrophied myocytes. We concluded that compensated ventricular hypertrophy results in a blunted contractile response to beta-AR stimulation, which is present at the cellular level and independent of alterations in inhibitory G proteins and the L-type Ca(2+) channel.

Impaired cell shortening and relengthening with increased pacing frequency are intrinsic to the senescent mouse cardiomyocyte

Increased heart rate enhances cardiac contractility and accelerates relaxation. Both the force- and relaxation-frequency relationships are critical to myocardial function, especially during stress, and have been shown to be impaired in senescent myocardium. While senescent myocardium is characterized by decreased sarcoplasmic reticulum calcium ATPase activity, it is unclear if altered calcium regulation is directly responsible for the attenuated contractility and relaxation observed with increasing pacing frequency in aged myocardium. We examined this issue using freshly dissociated left ventricular myocytes, isolated from young adult and senescent mouse hearts. Myocytes were paced from 2 to 9 Hz at 37 degrees C, and cell shortening and [Ca(2+)](i)were simultaneously measured using video edge-detection and fura-2 fluorescence, respectively. In adult myocytes, increasing the pacing rate resulted in a progressive increase in percent cell shortening (CS) (P<0.01). This positive CS-frequency relationship was paralleled by an increase in [Ca(2+)](i)transient amplitude (P<0.05). In contrast, the CS-frequency relationship was blunted in senescent myocytes with no increase in percent CS or [Ca(2+)](i)transient amplitude with increasing pacing rate. With increased pacing, the decreases in time constants (tau) of cell relengthening and Ca(2+)transient decay were much steeper in adult compared to senescent myocytes (P<0.05). This study demonstrates that adult mouse myocytes exhibit augmented intracellular Ca(2+)transient amplitude and enhanced intracellular Ca(2+)removal with increasing pacing frequency, resulting in increased cell shortening and enhanced relengthening with frequency. In contrast, senescent mouse myocytes exhibit impaired calcium handling with increasing pacing frequency, which correlated with impairment of both cell shortening and relengthening.

Chronic alpha-adrenergic receptor stimulation modulates the contractile phenotype of cardiac myocytes in vitro

BACKGROUND

Heart failure is characterized by contractile dysfunction of the myocardium and elevated sympathetic activity. We tested the hypothesis that chronic alpha-adrenergic (alpha-ADR) stimulation modifies the molecular and contractile phenotype of cardiac myocytes.

METHODS AND RESULTS

Adult rat ventricular myocytes in culture were exposed to alpha-ADR stimulation (norepinephrine + propranolol) for 48 hours. alpha-ADR stimulation decreased the mRNAs for sarcoplasmic reticulum Ca(2+)-ATPase and Ca(2+) release channel by 56% and 52%, respectively, and increased mRNA and protein for the Na(+)-Ca(2+) exchanger by 70% and 39%, respectively. After washout of the alpha-ADR agonist, simultaneous measurement of [Ca(2+)](i) transients with fura 2 and myocyte shortening by video edge-detection showed that [Ca(2+)](i) amplitude and myocyte shortening were decreased in alpha-ADR-treated myocytes, and the time to peak and time from peak to 80% decline of both [Ca(2+)](i) and myocyte shortening were increased. The concentration-response curve for myocyte shortening by the Na(+) channel activator veratridine was shifted leftward in alpha-ADR-stimulated myocytes (EC(50), 21.6+/-4.6 versus 105.8+/-10.5 nmol/L, P:<0.001).

CONCLUSIONS

Chronic alpha-ADR stimulation of cardiac myocytes causes decreases in the expression of sarcoplasmic reticulum Ca(2+)-ATPase and the Ca(2+) release channel that are associated with decreases in [Ca(2+)](i) and contractility. alpha-ADR stimulation simultaneously increases Na(+)-Ca(2+) exchanger expression, thereby increasing sensitivity to intracellular Na(+).

ATP synthesis during low-flow ischemia: influence of increased glycolytic substrate

BACKGROUND

Our goals were to (1) simulate the degree of low-flow ischemia and mixed anaerobic and aerobic metabolism of an acutely infarcting region; (2) define changes in anaerobic glycolysis, oxidative phosphorylation, and the creatine kinase (CK) reaction velocity; and (3) determine whether and how increased glycolytic substrate alters the energetic profile, function, and recovery of the ischemic myocardium in the isolated blood-perfused rat heart.

METHODS AND RESULTS

Hearts had 60 minutes of low-flow ischemia (10% of baseline coronary flow) and 30 minutes of reperfusion with either control or high glucose and insulin (G+I) as substrate. In controls, during ischemia, rate-pressure product and oxygen consumption decreased by 84%. CK velocity decreased by 64%; ATP and phosphocreatine (PCr) concentrations decreased by 51% and 63%, respectively; inorganic phosphate (P(i)) concentration increased by 300%; and free [ADP] did not increase. During ischemia, relative to controls, the G+I group had similar CK velocity, oxygen consumption, and tissue acidosis but increased glycolysis, higher [ATP] and [PCr], and lower [P(i)] and therefore had a greater free energy yield from ATP hydrolysis. Ischemic systolic and diastolic function and postischemic recovery were better.

CONCLUSIONS

During low-flow ischemia simulating an acute myocardial infarction region, oxidative phosphorylation accounted for 90% of ATP synthesis. The CK velocity fell by 66%, and CK did not completely use available PCr to slow ATP depletion. G+I, by increasing glycolysis, slowed ATP depletion, maintained lower [P(i)], and maintained a higher free energy from ATP hydrolysis. This improved energetic profile resulted in better systolic and diastolic function during ischemia and reperfusion. These results support the clinical use of G+I in acute MI.

Branch retinal artery occlusion after thyroid artery interventional embolization

PURPOSE

To report a case of branch retinal artery occlusion after thyroid artery interventional embolization.

METHODS

A 33-year-old man with hyperthyroidism complained of visual loss and scotoma in the left eye after thyroid artery interventional embolization. He underwent a full ophthalmologic examination, including fluorescein angiography.

RESULTS

Visual acuity was 20/25, with inferior and superior scotomas present in the left eye. Fluorescein angiography of the left eye revealed delayed filling of a superotemporal branch retinal artery and nonfilling of an inferotemporal branch retinal artery.

CONCLUSION

A small, but definite risk of retinal artery occlusion after thyroid artery interventional embolization should be considered.

Angiotensin II receptor blockade attenuates the deleterious effects of exercise training on post-MI ventricular remodelling in rats

OBJECTIVES

The effects of exercise training on LV remodelling following large anterior myocardial infarction (MI) remains controversial. Blockade of the renin-angiotensin system has been shown to prevent ventricular dilation and deleterious remodeling. We therefore tested, in a rat model of chronic MI, whether any potentially deleterious effects of exercise on post-MI remodelling could be ameliorated by angiotensin II receptor blockade.

METHODS

Male Wistar rats underwent coronary ligation or sham operation. Treatment with losartan (10 mg/kg/day) began 1 week post-MI and moderate treadmill exercise (25 m/min, 60 min/day, 5 days/week) was initiated 2 weeks post-MI. Systolic and diastolic pressure-volume relationships were measured in isolated, red-cell perfused, isovolumically beating hearts 8 weeks post-MI. Morphometric measurements were performed in trichrome stained cross sections of the heart. Five groups of animals were compared: sham (n=13), control MI (MI; n=11), MI plus losartan (MI-Los; n=13), MI plus exercise (MI-Ex; n=10) and MI plus exercise and losartan (MI-Ex-Los; n=12).

RESULTS

Infarct size (% of left ventricle, LV) was similar among the infarcted groups [MI=43+/-4%, MI-Los=49+/-2%, MI-Ex=45+/-1%, MI-Ex-Los=48+/-2% (NS)]. Exercise, losartan and exercise+losartan treatments all attenuated LV dilation post-MI to a similar degree. Exercise training increased LV developed pressure in both untreated and losartan treated hearts (P<0.05 vs. other MI groups). In addition, exercise resulted in additional scar thinning in untreated hearts, while no additional scar thinning was seen in post-infarct hearts receiving both losartan and exercise.

CONCLUSIONS

Following large anterior MI, losartan attenuated LV dilation and scar thinning. In untreated animals, exercise decreased dilation, but also contributed to scar thinning. Therefore, exercise concurrent with blockade of the renin-angiotensin system may provide optimal therapeutic benefit following large anterior MI.

Impaired lusitropy-frequency in the aging mouse: role of Ca(2+)-handling proteins and effects of isoproterenol

We examined the relationship between age-associated lusitropic impairment, heart rate, and Ca(2+)-handling proteins and assessed the efficacy of increasing left ventricular (LV) relaxation via beta-adrenergic stimulation in adult and aging mouse hearts. LV function was measured in isolated, isovolumic blood-perfused hearts from adult (5 mo), old (24 mo), and senescent (34 mo) mice. Hearts were paced from 5 to 10 Hz, returned to 7 Hz, exposed to 10(-6) M isoproterenol, and paced again from 7 to 10 Hz. Age-related alterations in Na(+)/Ca(2+) exchanger (NCX), sarcoplasmic reticulum (SR) Ca(2+)-ATPase (SERCA2a), and phospholamban (PLB) levels were assessed by immunoblot. Despite preserved contractile performance, aging caused impaired lusitropy. Increased pacing caused an elevation in end-diastolic pressure that progressively worsened with age. The time constant of isovolumic pressure decay (tau) was significantly prolonged in old and senescent hearts compared with adults. Relative to adult hearts, the SERCA2a-to-PLB ratios were reduced 68 and 69%, and NCX were reduced 37 and 58% in old and senescent hearts, respectively. Isoproterenol completely reversed the age-associated lusitropic impairments. These data suggest that impaired lusitropy in aging mouse hearts is related to a decreased rate of cytosolic Ca(2+) removal and that accelerating SR Ca(2+) resequestration via beta-adrenergic stimulation can reverse this impairment.

Elasticity and fracture strain of whole blood clots

The measurement of clot elasticity and fracture strain is carried out using a rotational rheometer with a controlled stress system. The elasticity is quantified by a shear elastic modulus and fracture strain by a critical strain (deformation) when the clot begins to break up. The results indicate a decrease of elasticity and increase of fracture strain of the clot with increasing hematocrit. Moreover, the elastic modulus of the clot is not constant but increasing with deformation.

C-alkylated spiro[benzofuran-3(2H),4'-1'-methyl-piperidine-7-ols] as potent opioids: a conformation-activity study

Among a series of C-alkylated analogs of the weak mu opioid ligand spiro[benzofuran-3(2H),4'-1'-methylpiperidine-7-ol] (1), the 2-methyl, 2-ethyl, and cis 3'-methyl analogs, namely compounds (+/-)2, (+/-)-3, and (+/-)-4, showed much enhanced mu-affinities, with (+/-)-4 being almost as potent as (-)-morphine; while the trans 3'-methyl analog (+/-)-5 remained a weak mu-binder. Energy calculations and nmr data indicated that compounds 2-4 favor phenyl-axial conformations, while compounds 1 and 5 favor phenyl-equatorial conformations.

Early changes in excitation-contraction coupling: transition from compensated hypertrophy to failure in Dahl salt-sensitive rat myocytes

OBJECTIVE

The aims were to (1) define the early changes in excitation-contraction coupling during the transition from cardiac hypertrophy to heart failure, and (2) to clarify the causal relationship between mechanical dysfunction and abnormal Ca2+ handling in the Dahl salt-sensitive rat model.

METHODS

Myocardial contractile function was assessed in whole heart perfusion studies. In separate experiments, isolated left ventricular myocytes from Dahl salt-sensitive (DS) and Dahl salt-resistant (DR) rats were paced at a physiological rate of 5Hz and cell shortening (CS) and [Ca2+]i measured simulataneously by video-edge detection and fura-2 fluorescence.

RESULTS

DS hearts developed hypertrophy after 4 weeks of a high-salt diet (4WHSD), as indicated by a 26% increase (p < 0.01) in the heart to body weight ratio and a 21% increase (p < 0.01) in cell width. Heart failure developed after 12 weeks of a high-salt diet (12WHSD), as indicated by an 11% increase (p < 0.01) in the lung wet to dry weight ratio. Furthermore, in DS-12WHSD hearts, the diastolic pressure-volume relationship had shifted rightward. DR rats did not develop hypertension and seved as age-matched controls. A 31% (p < 0.05) increase in the %CS in DS-4WHSD myocytes compared to DR-4WHSD myocytes with a trend of a parallel increase in Ca2+ transient amplitude was found. There was no difference in the Ca2+ transient parameters between DR and DS at 12WHSD, but an 18% (p < 0.01) decrease occurred in peak [Ca2+]i in DS myocytes between 4WHSD and 12WHSD. In DS-12WHSD, the time to peak shortening and the time from peak shortening to 50% and 90% relaxation was significantly prolonged by 27%, 44%, and 38%, respectively, as compared to the age-matched DR myocytes.

CONCLUSION

Our results indicated that: (I) normal Ca2+ homeostasis is preserved at the stage of compensated hypertrophy; (2) the early signs of isolated myocyte dysfunction were a prolongation of the shortening and relaxation time course without an abnormal time course of the Ca2+ transient. Thus, in the hypertensive Dahl salt rat model, abnormal Ca2+ handling appears neither to precede nor initiate the transition to failure.

Animal models of cardiovascular disease for pharmacologic drug development and testing: appropriateness of comparison to the human disease state and pharmacotherapeutics

For proper drug development, targeting and testing the use of suitable animal models that are well controlled with regard to duration, degree, and stage of the disease are vitally needed. Furthermore reliable phenotyping and genotyping with regard to functional physiology as well as cellular biochemistry and molecular biology are vital to early decision making in drug discovery, development, and successful clinical development. The use of animal models allows the design of clinical trials without the complication of having to impose "accepted treatment modalities" on top of investigative agents. With the availability of human myocardium for study as a result of cardiac transplantation programs, experimental findings previously reported in several animal models of heart disease have been questioned with regard to suitability for comparison to the human condition. With the development and application of sophisticated techniques and biochemical assays to the study of heart tissue several adaptive changes have been identified and labeled "markers of heart failure." Several animal models share some of these adaptive changes in common with failing human myocardium, but not others. The goal of this report is to point out similarities and differences reported to date in failing and nonfailing human myocardium to that reported in animal models of human heart disease. This discussion indicates important dissimilarities found in several key animal models that have resulted in the development of cardioactive agents and therapeutic interventions for the treatment of human heart disease and the unexpected outcomes. Although focusing on heart failure, a vital goal of this report is to emphasize some key principles supporting the need for clear, comprehensive, and unbiased evaluation of animal models currently in use to study any disease condition, as well as the need for further model development and study in open collaborative efforts.

Decreased energy reserve in an animal model of dilated cardiomyopathy. Relationship to contractile performance

An animal model was used to test the hypothesis that in heart failure the decrease in the ability to resynthesize ATP through the creatine kinase (CK) reaction (which we call energy reserve) contributes to the inability of the heart to maintain its normal function and contractile reserve. One-week-old turkey poults were fed furazolidone for 14 days to induce dilated cardiomyopathy. Isolated Langendorff-perfused hearts from these myopathic animals showed a 73% decrease in baseline isovolumic contractile performance. Neither increasing [Ca2+]o nor electrical pacing rate increased isovolumic contractile performance. Measured by 31P nuclear magnetic resonance magnetization transfer and chemical assay, ATP concentration was decreased by 23%, phosphocreatine concentration by 42%, CK enzyme activity by 34%, and the pseudo first-order rate constant for the CK reaction by 50%. Measured CK reaction velocity decreased by 71%. The reduced ability to increase cardiac performance in response to increasing [Ca2+]o in hearts with lower CK reaction velocity was reproduced in part by feeding a separate group of turkey poults beta-guanidino-propionic acid to specifically reduce CK reaction velocity by decreasing guanidino substrate concentration. These hearts had normal baseline performance but blunted contractile reserve. These observations provide further support for the hypothesis that a decrease in energy reserve via the CK system contributes to reduced cardiac function in the failing heart.

Effect of a high omega-3 fatty acid diet on cardiac contractile performance in Oncorhynchus mykiss

OBJECTIVE

Omega-3 fatty acids have been implicated in the amelioration of cardiovascular disease in humans. Since these fatty acids are found in salmonid fish and are known to be essential for all salmonids, this study was undertaken to determine the effect of a high dietary intake of omega-3 fatty acids on the function of trout myocardium.

METHODS

Rainbow trout (Oncorhynchus mykiss) from a single stock population were divided into two groups and fed either a diet high in omega-3 fatty acids (i.e. 4.0%) or low in omega-3 fatty acids (i.e. 2.1%) for 3 months. Heart function was studied at the whole heart and isolated muscle level.

RESULTS

In whole heart preparations, peak developed pressures in freely ejecting hearts from salmonids fed the high omega-3 fatty acid diet were significantly greater than the hearts from salmonids fed the low omega-3 fatty acid diet (21 +/- 1.5 vs. 11.5 +/- 0.9 mmHg respectively, P < 0.05). These data correlated with results from isolated muscle preparations of myocardium from fish fed high and low omega-3 fatty acid diets (4.12 +/- 0.32 vs. 3.08 +/- 0.28 mN/mm2 respectively, P < 0.05). The calcium uptake rate of heart homogenates from fish fed the high omega-3 diet was slower and sarcoplasmic reticulum Ca2+ ATPase activity was lower. The myofilament force-calcium relationship in myocardium from trout fed the low omega-3 diet was shifted leftward on the calcium axis to lower intracellular calcium concentrations (delta 0.4 pCa units) compared to mammalian myocardium. This resulted in greater activation at lower intracellular calcium concentrations. However, trouts fed diets high in omega-3 fatty acids had [Ca2+] required for half maximal activation more similar to what has been reported for mammalian myocardium (delta 0.1 pCa unit). Furthermore, the myofilaments of trout hearts appear to show less cooperativity (Hill coefficient approximately 1) than has been found in mammalian myocardium (Hill coefficient > or = 2).

CONCLUSIONS

Our experimental results demonstrate for the first time that dietary omega-3 fatty acid content affects myocardial force of contraction by affecting calcium metabolism and myofilament calcium-activation.

Is contractility depressed in the failing human heart?

Is contractility depressed in the failing human heart? The question must be approached in a stringent manner. Myocardium from failing human hearts has been shown to generate normal physiological force under the ideal conditions of low stimulation and an adequate energy supply. Nevertheless, even when subjected to physiologically conducive conditions, failing myocardium experiences a slowed relaxation, adversely affecting the diastolic properties of the heart. In addition, experiments have shown that increasing the contraction rates of failing hearts clearly results in lowered force and pressure evolution. This information indicates a decrease in contractile reserve in both a systolic and diastolic sense. Not surprisingly, the term end-stage heart failure becomes questionable when applied to myocardium obtained from patients undergoing cardiac transplantation. A number of studies involve such myocardium from feasible regions of the heart perfused within ideal physiological conditions yielding, at times, nonfailing performance. Therefore, it becomes imperative to bear in mind the role of such myocardium within the framework of the entire diseased heart.

Comparison of twitch force and calcium handling in papillary muscles from right ventricular pressure overload hypertrophy in weanling and juvenile ferrets

OBJECTIVE

The aim was to compare differences in peak twitch force occurring despite similar degrees of right ventricular hypertrophy in ferrets with pulmonary artery banding at either weanling or juvenile age.

METHODS

After inducing pressure overload hypertrophy by banding the pulmonary artery of weanling and juvenile age ferrets, mechanical function (that is, isometric twitch force and passive stiffness), intracellular [Ca2+] using the calcium indicator aequorin, markers of myocardial energy supply, and quantified connective tissue content were studied.

RESULTS

It was previously found that there was a reduced peak isometric twitch force despite normal [Ca2+]i in juvenile banded ferrets age 10-12 weeks with right ventricular pressure overload hypertrophy (POHj). In the present study we report findings in banded weanling ferrets (POHw) age 7 weeks. POHw animals showed a similar degree of hypertrophy to that found in the POHj. However, there was a greater peak twitch force in hypertrophied muscles at higher [Ca2+]o. There was no difference in peak [Ca2+]i: -3.1(SEM 0.1) v -3.1(0.3) (log fractional luminescence) at 16 mM [Ca2+]o for control and POHw, respectively. Connective tissue content for control animals was 10(1)% versus 10(2)% in POHw. Despite a lack of quantitative change in connective tissue content or resting [Ca2+]i in POHw, passive stiffness in papillary muscles was increased. Retrospective analysis of tissue from POHj revealed a connective tissue content of 24(6.8)% (P << 0.001). Thus the decreased peak twitch force reported in POHj might in part be due to an increase in fibrous connective tissue. In this study, lactate dehydrogenase was significantly higher (38%) in POHw animals. In contradistinction, total creatine kinase activity and total creatine content were significantly less (22%) in hearts from POHj animals, indicating differences in myocyte remodelling despite similar degrees and durations of hypertrophy.

CONCLUSIONS

Comparison of POHw and POHj showed that, when there is restructuring of the extracellular space in terms of increased fibrosis, there is also molecular remodelling in the myocyte, as demonstrated by a decrease in the creatine kinase system.

Enalapril treatment increases cardiac performance and energy reserve via the creatine kinase reaction in myocardium of Syrian myopathic hamsters with advanced heart failure

BACKGROUND

Converting enzyme inhibitor treatment of congestive heart failure slows progression to failure and reduces mortality rate. It is known whether these benefits are due solely to improved hemodynamics or also to improved myocyte energetics. This study examines the effect of enalapril treatment on both isovolumic contractile performance and its biochemical correlate, flux through the creatine kinase (CK) system, in an animal model of severely failing myocardium.

METHODS AND RESULTS

Seven-month-old Syrian cardiomyopathic (TO-2 strain) and normal golden Syrian (FIB strain) hamsters were each randomly assigned to one of three groups supplied daily with either no, low (25 mg/kg body wt), or high (100 mg/kg body wt) doses of enalapril for 12 to 14 weeks. At 10 months of age, all substrates and products and flux through the CK reaction were measured in isolated perfused hearts by 31P magnetization transfer and chemical assay. Compared with normal hamsters, the myopathic hamsters exhibited significantly lower body weights and higher biventricular heart weights, which were partially reversed by drug treatment. The Langendorff-perfused hearts showed decreased isovolumic contractile performance with identical load conditions. This was partially reversed by drug treatment. In the failing hearts, the following substrate and product concentrations and enzyme activities were decreased compared with nonfailing hearts but were unchanged by drug treatment: ATP (-28%), phosphocreatine (-48%), free creatine (-64%), ADP (-51%), and CK (-34%, primarily MM isoenzyme). Flux through the CK reaction for the untreated cardiomyopathic hamster hearts was decreased by 67%, and this decrease was almost completely reversed by enalapril treatment. The increased CK flux is due to an increase in the rate constant for the reaction, since substrate concentrations are unchanged, and is not predicted by the rate equation. In enalapril-treated failing hearts, phosphoryl transfer via the CK reaction increased with contractile performance. This was not observed in the nonfailing hearts, in which energy reserve is adequate to support changes in contractile performance.

CONCLUSIONS

Decreased flux through CK reaction leads to decreased capacity for ATP synthesis and may contribute to decreased contractile performance in cardiomyopathic hamster hearts. Enalapril treatment results in increased phosphoryl transfer through the CK reaction in failing myocardium, and this increase is coupled to improved cardiac performance. Decreased CK flux in failing hearts is due to a combination of decreased Vmax and lower guanidino pool; this mechanism fails to explain changes in CK flux in enalapril-treated failing hearts.

The relation of the location of haptics of posterior chamber intraocular lenses and peripheral anterior synechia

PURPOSE

To investigate the occurrence, outcome and influencial factors of the peripheral anterior synechia (PAS) following implantation of posterior chamber intraocular lenses for finding a way to reduce the PAS.

SUBJECTS

40 eyes of 38 senile cataract patients with normal chamber angle and intraocular pressure (IOP) preoperatively were examined.

METHODS

Extracapsular cataract extraction was performed under microscope with insertion of a posterior chamber lens implant vaulted anteriorly by 10 degrees. Gonioscopy and slit-lamp examination and photography of the operated eyes were performed 3 to 6 months postoperatively.

RESULTS

PAS were found in 20 (50%) of the 40 eyes. Among the 20 eyes with PAS the locations of 23 haptics in 17 eyes corresponded with those of the PAS. PAS were seen more frequently with vertically sulcus-fixated haptics than with the horizontally capsular-fixated haptics, showing a significant difference (P < 0.05). 88% of the eyes with PAS had pupillary deformation, but their visual acuities and IOP were not affected.

CONCLUSIONS

PAS is more likely to occur with vertically sulcus-fixated IOL. Rotating the capsular-fixated haptics to the horizontal position may reduce the incidence of PAS. Gonioscopy should be a routine follow-up examination.

[Gonioscopic observation after posterior chamber intraocular lens implantation]

6 months after senile extra-capsular cataract extraction and posterior chamber intraocular lens (IOL) implantation, Goldmann gonioscopy was performed on 30 eyes having undertaken the surgery. Peripheral anterior synechiae (PAS) were found in 17 eyes (56%). PAS overlying the positions of 20 lens haptics were observed in 15 eyes. It is easier to develop PAS in eyes with vertically fixed haptics than in eyes with horizontally fixed ones. The causes and the consequences of PAS were discussed. It is suggested that during the follow-up, routine gonioscopic observation after posterior chamber IOL implantation be necessary.

Coupling of calcium to the interaction of troponin I with troponin C from cardiac muscle

The interaction of troponin I (CTnI) with troponin C (CTnC) from bovine cardiac muscle was studied using CTnC modified at Cys35 and Cys84 with the fluorescent probe 2-[(4'-iodoacetamido)-anilino]naphthalene-6-sulfonic acid (CTnCIAANS). The association constant for complex formation between the two proteins was determined at 20 degrees C in 0.4 M KCl, 1 mM DTT, 1 mM EGTA, and 25 mM MOPS, pH 7.2. In the presence of EGTA, Mg2+, and Ca2+ these constants were 1.46 x 10(7), 4.1 x 10(7), and 12.7 x 10(7) M-1, respectively, with corresponding free energy values of -9.62, -10.23, and -10.88 kcal mol-1. The CTnI-CTnCIAANS complex was stabilized by -0.61 kcal when the two Ca/Mg sites of CTnCIAANS were saturated with Mg2+ and by -1.26 kcal when all three Ca2+ sites were occupied by Ca2+. These results suggest that calcium activation in cardiac muscle may be accompanied by a coupling free energy of -0.65 kcal. This value is a factor of 4 smaller than the value previously determined, using a similar method, for the (troponin I).(troponin C) complex from skeletal muscle [Wang, C.-K., & Cheung, H.C. (1985) Biophys. J.48, 727-739]. Since CTnC has only one Ca(2+)-specific site and troponin C from skeletal muscle has two such sites, the present result is a factor of 2 smaller than that for the skeletal complex on the basis of a single specific site. Phosphorylation of CTnI by 3',5'-cyclic AMP-dependent protein kinase resulted in a decrease of the association constants by a factor of 2.5-3.5.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of MCI-154 and caffeine on Ca(++)-regulated interactions between troponin subunits from bovine heart

We studied the effects of MCI-154 (6-[4-(4-pyridyl)aminophenyl]-4,5- dihydro-3(2H)-pydridazinone hydrochloride) and caffeine on the regulation of Ca++ in the interaction between troponin subunits from bovine hearts by using fluorescence spectroscopy. The titration of MCI-154 to bovine cardiac troponin C (TnC) resulted in a concentration-dependent change in intrinsic fluorescence, indicating that MCI-154 may induce conformational changes and perturb the microenvironments of the intrinsic fluorophores. MCI-154-induced changes in the rotational correlation times obtained from fluorescently modified TnC and its complex with cardiac troponin I (TnI) indicate that the effect of MCI-154 may be highly correlated with a gross alteration in the overall molecular shape of TnC. A right shift in the-fluorescence curve with a significant decrease in maximal fluorescence intensity was observed in the presence of MCI-154 in isolated TnC, indicating a decrease in the affinity of TnC for Ca++. However, in the reconstituted binary (TnC.TnI) and ternary (TnC.TnI.TnT) complexes the pCa-curve was shifted to the left under similar conditions. These data indicate that the complexation of TnC with TnI and TnT resulted in an increase in the affinity of TnC for Ca++ in the presence of MCI-154. In the studies of caffeine effect, the results showed that the effect of caffeine on isolated TnC was similar to that of MCI-154. Caffeine (0.5 microM) shifted the pCa-fluorescence curve to the right by 0.4 U in the binary complex and to the left by 0.2 U in the ternary complex at pCa50% when compared to the curve in the absence of caffeine.(ABSTRACT TRUNCATED AT 250 WORDS)

[Ca2+]i in human heart failure: a review and discussion of current areas of controversy

Multiple abnormalities have been reported in the setting of human heart failure. It is unclear whether detected changes reflect adaptive alterations in myocardium subjected to increased and sustained hemodynamic overload or are pathogenic to the disease process. As a result of the observation that the primary defect in heart failure is decreased pump function, investigators have concentrated their efforts on determining systolic [Ca2+]i as a logical corollary and a causative mechanism for contractile dysfunction. A simple cause and effect relationship has therefore been proposed with regard to contractile dysfunction and [Ca2+]i. Yet some investigators have found no difference in peak systolic [Ca2+]i between failing and non-failing human myocardium, whereas others have found peak [Ca2+]i to be significantly reduced in failing hearts. Resting calcium concentrations have been reported either to be elevated in failing human myocardium or not different from non-failing human myocardium. Investigators should now appreciate that the force-calcium relationship is not a simple relationship. One must take into account the prolonged time course and slowed mobilization of [Ca2+]i as opposed to simply peak [Ca2+]i. When put in perspective of mechanisms and determinants of the Ca(2+)-force relationship, we begin to realize that failing human myocardium has the "potential" to generate normal levels of force. Only when stressed by [Ca2+]i overload and/or frequency perturbation does myocardium from patients with end-stage heart disease demonstrate contractile failure. Although [Ca2+]i availability and mobilization are likely to play a role in the systolic as well as diastolic dysfunction reported in human heart failure, it is likely that other mechanisms are involved as well (e.g., myocardial energetics). Myocardial energetics is directly related to [Ca2+]i and mobilization in failing human myocardium, because metabolites, e.g., ADP, inhibit pumps, such as sarcoplasmic reticulum Ca2+ ATPase activity. We therefore conclude that there is a role for intracellular calcium mobilization and myocardial energetics for systolic and diastolic dysfunction seen in human heart failure.

Pathophysiological and biochemical characterisation of an avian model of dilated cardiomyopathy: comparison to findings in human dilated cardiomyopathy

OBJECTIVE

With the recent availability of human myocardium, many animal models have been shown to be unsuitable as models of human heart failure. The aim of this study was to describe the pathophysiological changes in a model of dilated cardiomyopathy in turkey poults and to compare them to results obtained from failing human hearts.

METHODS

After receiving furazolidone for 2-3 weeks, animals developed cardiomyopathy (Fz-DCM) and were studied at the whole heart and isolated muscle level. Myofibrillar ATPase activity and noradrenaline turnover were determined in tissue homogenates in failing and non-failing control hearts.

RESULTS

Fz-DCM animals had greater heart weights, heart weight/body weight ratios, and end diastolic volumes. Fractional shortening of the left ventricle and systolic blood pressures were reduced (p < 0.01) in myopathic animals. Isolated perfused hearts had lower peak developed pressures (p < 0.01). Isolated muscle preparations showed no significant differences in peak twitch forces between control and Fz-DCM muscles at a 1 Hz stimulation rate. The relationship between force and frequency of stimulation was positive in control muscles up to 1.7 Hz, whereas in Fz-DCM muscles the relationship was sharply negative above 1 Hz. Time to 80% relaxation was markedly slower in the Fz-DCM muscles. Although [Ca2+]o responsiveness was similar for Fz-DCM and normal animals, responsiveness to isoprenaline was significantly reduced in Fz-DCM hearts. Cardiomyopathic animals displayed diminished noradrenaline content in the left ventricle. Fractional noradrenaline turnover was higher (p < 0.05) in the cardiomyopathic birds. In skinned fibre preparations from control and Fz-DCM hearts calcium activations were similar. Maximum myofibrillar ATPase activities were, however, significantly lower in myopathic animals and myofibrillar protein content was reduced by 25%.

CONCLUSIONS

In this model of dilated cardiomyopathy: (1) relaxation is markedly prolonged; (2) the response to beta adrenergic stimulation is diminished; (3) Mg-ATPase activities and myofibrillar protein content are reduced; and (4) sympathetic activity in the heart is markedly increased with depletion of noradrenaline stores. Furthermore, a reduction in tissue noradrenaline content per se is a misleading index of the dynamic state of cardiac noradrenaline stores. With its similarities to human cardiomyopathy, this model promises to provide new insights into the pathophysiology and progression of dilated cardiomyopathy.