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R Liao

Publications and source records attributed to R Liao.

At least 19 recordsLinked to original sources
PubMed1998

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.

Magnetic Resonance Spectroscopy↗
PubMed1998

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.

Animals↗
PubMed1996

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.

Adenosine Triphosphate↗
PubMed1996

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.

Actin Cytoskeleton↗
PubMed1995

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.

Animals↗
PubMed1995

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.

Calcium↗
PubMed1995

[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.

Adult↗
PubMed1995

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.

Animals↗
PubMed1995

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.

Adult↗
PubMed1994

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)

Animals↗
PubMed1994

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)

Animals↗
PubMed1993

Rotational dynamics of skeletal muscle troponin C.

Upon excitation by 280 nm, the intensity decay of the 2 tyrosine residues (residues 10 and 109) of rabbit skeletal muscle troponin C is resolved into three components. The anisotropy decay in the absence of divalent cation is biphasic with a short correlation time of 0.67 ns and a long correlation time of 9.23 ns. The limiting anisotropy is 0.225, considerably lower than the value expected for immobilized tyrosine. Upon excitation by 290 nm, the anisotropy decay is also biphasic, and the limiting anisotropy increases to 0.274. The recovery of anisotropy by excitation at a wave-length near the red edge of the tyrosine absorption spectrum is evidence of fluorescence resonance energy transfer between the two tyrosines. For energy transfer to occur, the average separation between the 2 tyrosines is unlikely much larger than the Förster distance Ro, congruent to 10 A, and this close proximity of the residues would require a highly distorted dumbbell shape of troponin C in solution. These results are consistent with a flexible central helix, which either has a segmental flexibility with large amplitude or results in a spectrum of conformations including those in which the two globular domains are in a very close proximity.

Animals↗
PubMed1993

Phosphocreatine T1 measurements with and without exchange in the heart.

The intrinsic phosphocreatine (PCr) T1 values measured by time-dependent magnetization transfer in isolated perfused rat, hamster, and turkey hearts were indistinguishable. The value of 3.5 +/- 0.3 s for the rat heart is similar to values measured by other magnetization transfer methods. Irreversibly inhibiting the phosphoryl exchange between PCr and ATP in the rat heart using iodoacetamide changed the apparent T1 values of the two exchanging species when measured by inversion recovery: The apparent T1 of PCr increased from 1.92 +/- 0.06 s to 3.55 +/- 0.06 s, in excellent agreement with the intrinsic T1 measured by magnetization transfer. The apparent T1 of [gamma-P]ATP decreased from 0.92 +/- 0.07 s to 0.44 +/- 0.03 s. The value for the T1 of [gamma-P]ATP in hearts with inhibited phosphoryl exchange was similar to T1 values for [alpha-P]ATP and [beta-P]ATP, which remained unchanged. This illustrates that apparent T1 values for PCr and [gamma-P]ATP measured by inversion recovery in the presence of exchange are average T1 values in between the intrinsic values. The large differences between the intrinsic T1 measured by magnetization transfer and the T1 measured by inversion recovery makes the use of the appropriate value in different applications quantitatively important.

Adenosine Triphosphate↗
PubMed1993

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.

Adenosine Triphosphatases↗
PubMed1993

Differences in cardioprotective efficacy of adrenergic receptor antagonists and Ca2+ channel antagonists in an animal model of dilated cardiomyopathy. Effects on gross morphology, global cardiac function, and twitch force.

Turkey poults fed furazolidone (Fz) in high concentrations (700 ppm) develop dilated cardiomyopathy (Fz-DCM). We tested whether five cardioactive agents were cardioprotective in this model of heart failure, ie, whether they prevented dilatation and wall thinning and improved contractile performance. We compared the effects of chronic administration of a beta 1-selective and a nonselective beta-receptor antagonist, an alpha-receptor antagonist, and two Ca2+ channel antagonists in the presence of Fz administration. The greatest cardioprotection was found with treatment with either propranolol or nifedipine. At the gross morphological level, the effect of propranolol (a nonselective beta-adrenergic antagonist) was greater than the effect of atenolol (a selective beta 1-adrenergic antagonist), and the effect of nifedipine was greater than that of verapamil (Ca2+ channel antagonists), with all agents more cardioprotective than phenoxybenzamine (an alpha 1-adrenergic > alpha 2-adrenergic antagonist). Differences in cardioprotective efficacy of each agent increased with increased concentration. These data indicate that the dose and choice of a specific type of Ca2+ channel antagonist or beta-receptor antagonist might be important in the treatment of dilated cardiomyopathy. All agents that were cardioprotective caused similar functional improvements at both the whole heart and isolated muscle levels. Compared with control animals, Fz-DCM animals showed a significant reduction in peak left ventricular (LV) developed pressure (92 +/- 17 versus 143 +/- 24 mm Hg, P < .05), +dP/dt (1151 +/- 219 versus 2454 +/- 549 mm Hg/s), and -dP/dt (1128 +/- 291 versus 1875 +/- 396 mm Hg/s), with a significant increase in LV end-diastolic volumes (2.8 +/- 0.7 versus 0.16 +/- 0.1 mL for control animals, P < .05). In contradistinction, LV + dP/dt and -dP/dt values for animals receiving Fz plus a cardioactive agent that demonstrated cardioprotection were not significantly different from control values. Peak LV developed pressures were also similar for Fz animals receiving an agent that demonstrated cardioprotection and control animals not receiving any pharmacologic agent. Isolated muscles from Fz-DCM animals as well as animals receiving Fz plus cardioprotective pharmacologic agents responded normally with regard to increasing extracellular Ca2+ concentrations. Peak twitch forces were greater for animals receiving cardioprotective agents plus Fz than control animals not receiving any pharmacologic agents or Fz alone. At higher stimulation rates, Fz-DCM muscles demonstrated a significantly reduced peak twitch force (4 +/- 0.5 versus 1.5 +/- 0.4 g/mm2 for control muscles versus Fz-DCM muscles, respectively).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Nanosecond study of fluorescently labeled troponin C.

The time-resolved extrinsic fluorescence of rabbit skeletal troponin C was studied with the protein labeled at Cys-98 with N-(iodoacetyl)-N'-(5-sulfo-1-naphthyl)ethylenediamine. Both the intensity and anisotropy decays followed a biexponential decay law, regardless of the ionic condition, pH, viscosity or temperature. The lifetimes and their fractional amplitudes were insensitive to Mg2+, and the lifetimes were also insensitive to Ca2+. In response to Ca2+ binding to all four sites, the fractional amplitude (alpha 1) associated with the short lifetime (tau 1) decreased by a factor of two, thus increasing the ratio of the two amplitudes alpha 2/alpha 1 from 1.6 to 4.3. These amplitude changes suggest the existence of two conformational states of TnC-IAEDANS, with the conformation associated with the long-decay component (tau 2) being promoted by saturation of the two Ca(2+)-specific sites. At pH 5.2 the ratio alpha 2/alpha 1 for the apo-protein was 3.5 indicating different relative populations of the two decay components when compared with pH 7.2. In the presence of Ca2+ at the lower pH, alpha 2/alpha 1 decreased to 2.1, suggesting a shift of the conformations in favor of the short-decay component. Thus Ca2+ elicited different conformational changes in TnC at the two pH values. The recovered anisotropies suggest that there were fast molecular motions that were not resolved in the present experiments, and some of these motions were sensitive to Ca2+ binding to the specific sites. These results support the notion of communication between the N-domain and the C-terminal end of the central helix of troponin C.

Animals↗
PubMed1992

Time-resolved tryptophan emission study of cardiac troponin I.

We have carried out a time-resolved fluorescence study of the single tryptophanyl residue (Trp-192) of bovine cardiac Tnl (CTnl). With excitation at 300 nm, the intensity decay was resolved into three components by a nonlinear least-squares analysis with lifetimes of 0.60, 2.22, and 4.75 ns. The corresponding fractional amplitudes were 0.27, 0.50, and 0.23, respectively. These decay parameters were not sensitive to complexation of CTnl with cardiac troponin C (CTnC), and magnesium and calcium had no significant effect on the decay parameters. After incubation with 3':5'-cyclic AMP-dependent protein kinase, the intensity decay of CTnl required a fourth exponential term for satisfactory fitting with lifetimes of 0.11, 0.81, 1.95, and 6.63 ns and fractional amplitudes of 0.06, 0.37, 0.27, and 0.29, respectively. When bound to CTnC, the intensity decay of phosphorylated CTnl (p-CTnl) also required four exponential terms for satisfactory fitting, but the longest lifetime increased by a factor of 1.7. The decay parameters obtained from the complex formed between p-CTnl and CTnC were not sensitive to either magnesium or calcium. The anisotropy decay was resolved into two components with rotational correlation times of 0.90 and 23.48 ns. Phosphorylation resulted in a decrease of the long correlation time to 14.61 ns. The anisotropy values recovered at zero time suggest that the side chain of the Trp-192 had considerable subnanosecond motional freedom not resolved in these experiments. Within the CTnl.CTnC complex, the unresolved fast motions appeared sensitive to calcium binding to the calcium-specific site of CTnC. The observed emission heterogeneity is discussed in terms of possible excited-state interactions in conjunction with the predicted secondary structure of CTnl. The loss of molecular asymmetry of cardiac troponin I induced by phosphorylation as demonstrated in this work may be related to the known physiological effect of beta-agonists on cardiac contractility.

Animals↗