Evidence for covalent bonding of aryl groups to MnO2 nanorods from diazonium-based grafting.

We show here that the surface of MnO2 nanorods can be modified with aryl groups by grafting from aqueous and non-aqueous solutions of aryldiazonium salts. X-ray photoelectron spectroscopy provides direct evidence for covalent bonding of aryl groups to MnO2 through surface oxygens.

The mid-infrared (attenuated total reflection) spectroscopy of ethylene carbonate in water.

Ethylene carbonate (EC) and water solution compositions ranging from pure water to 60 mass% EC have been examined using infrared (attenuated total reflection) spectroscopy. The fundamental vibrational modes of EC in the mid-infrared between 2050 and 1000 cm(-1) were fitted to mixed Lorentzian-Gaussian bandshapes. The spectral data for EC bands between 1000 and 650 cm(-1) are also shown but were not curve-fitted due to baseline distortions from water librational modes. The results of the band analysis have provided information regarding the molecular structure of these solutions, and the fact that the structure is also concentration dependent. The Fermi resonance coupling between the v2 and 2v7 vibrations of EC have been analysed using a standard perturbation model.

The relationship between QT intervals and mortality in ambulant patients with chronic heart failure. The united kingdom heart failure evaluation and assessment of risk trial (UK-HEART)

AIMS: Mortality in patients with heart failure remains high and is difficult to predict. QT interval parameters on a 12-lead ECG have been shown to predict arrhythmic events in patients with a variety of myocardial diseases. There is some, but not consistent, evidence that QT interval parameters may act as predictors of mortality, in particular sudden death, in patients with heart failure. In an adequately powered prospective study we have studied QT interval parameters in patients with stable chronic heart failure in order to determine whether they are predictive of all-cause mortality or mode of death. METHODS AND RESULTS: Five hundred and fifty-four ambulant outpatients with chronic heart failure were recruited. A 12-lead ECG, chest radiograph, echocardiogram, 24 h ambulatory electrocardiogram and serum for biochemical analysis were obtained at baseline. Patients were followed for 471+/-168 days. QT intervals were measured in all leads blinded to patient's characteristics and outcome, were corrected for heart rate, and the maximum QT intervals, and QT dispersion (range of QT intervals) were determined. The same parameters were determined for JT intervals. The primary end-point was all-cause mortality, secondary end-points were sudden cardiac death and death due to progressive heart failure. Multivariate analysis with the Cox's proportional hazards model was used to determine which variables were independently related to outcome. Four hundred and ninety-five patients had analysable ECGs at study entry and of these 71 died during follow-up. The heart rate corrected QT dispersion and maximum QT interval were significant univariate predictors of all-cause mortality (P=0.026 and <0.0001 respectively), and also of sudden death and progressive heart failure death, but were not related to outcome in the multivariate analysis. The independent predictors of all-cause mortality were cardiothoracic ratio (P=0.0003), creatinine (P=0.0009), heart rate (P=0.007), echocardiographically derived left ventricular end-diastolic dimension (P=0.007) and ventricular couplets on 24 h electrocardiographic monitoring (P=0.015). CONCLUSION: In an adequately powered prospective study none of the QT or JT parameters were shown to be independent predictors of outcome in patients with mild to moderate congestive heart failure. These variables do not therefore add to the prognostic information which can be gained from simple radiographic, biochemical, echocardiographic and Holter data in this group of patients.

Effects of losartan and captopril on QT dispersion in elderly patients with heart failure. ELITE study group.

Differences in QT dispersion (a predictor for sudden death) were observed in a subgroup of patients in the ELITE heart failure study of losartan compared with captopril, and may explain improved survival with losartan.

Prospective study of heart rate variability and mortality in chronic heart failure: results of the United Kingdom heart failure evaluation and assessment of risk trial (UK-heart).

BACKGROUND: Patients with chronic heart failure (CHF) have a continuing high mortality. Autonomic dysfunction may play an important role in the pathophysiology of cardiac death in CHF. UK-HEART examined the value of heart rate variability (HRV) measures as independent predictors of death in CHF. METHODS AND RESULTS: In a prospective study powered for mortality, we recruited 433 outpatients 62+/-9.6 years old with CHF (NYHA functional class I to III; mean ejection fraction, 0.41+/-0.17). Time-domain HRV indices and conventional prognostic indicators were related to death by multivariate analysis. During 482+/-161 days of follow-up, cardiothoracic ratio, SDNN, left ventricular end-systolic diameter, and serum sodium were significant predictors of all-cause mortality. The risk ratio for a 41.2-ms decrease in SDNN was 1.62 (95% CI, 1.16 to 2.44). The annual mortality rate for the study population in SDNN subgroups was 5.5% for >100 ms, 12.7% for 50 to 100 ms, and 51.4% for <50 ms. SDNN, creatinine, and serum sodium were related to progressive heart failure death. Cardiothoracic ratio, left ventricular end-diastolic diameter, the presence of nonsustained ventricular tachycardia, and serum potassium were related to sudden cardiac death. A reduction in SDNN was the most powerful predictor of the risk of death due to progressive heart failure. CONCLUSIONS: CHF is associated with autonomic dysfunction, which can be quantified by measuring HRV. A reduction in SDNN identifies patients at high risk of death and is a better predictor of death due to progressive heart failure than other conventional clinical measurements. High-risk subgroups identified by this measurement are candidates for additional therapy after prescription of an ACE inhibitor.

A faster twitch contraction of soleus in the spontaneously hypertensive rat is partly due to changed fibre type composition.

Contractile properties and fibre type composition of slow-twitch soleus muscles from spontaneously hypertensive rats (SHR) were compared with those from a control normotensive strain (Wistar-Kyoto, WKY). Male rats aged around 100 days were used, and muscle tension was recorded isometrically in vitro. Tetanic tension was reduced by about 15% in SHR; this decrease was highly significant when tension was expressed relative to muscle cross-sectional area. Twitch contraction and relaxation were 12-15% faster in SHR. There were no differences in the rate of rise of tension of either tetani or twitches, but the relaxation of tetanic tension was 17% faster in SHR. Twitch:tetanus ratios were 20% smaller in SHR. Histochemistry showed that SHR muscles had a threefold higher proportion of fast type II fibres compared to WKY. There were no significant changes in the contractile properties of the fast-twitch extensor digitorum longus (EDL) muscles of SHR compared with WKY. Whilst the higher proportion of type II fibres could account for some of the contractile changes in SHR soleus muscles, the lack of any difference in the rate of rise of twitch and tetanic tension is not consistent. The faster rate of relaxation of both twitch and tetanus in SHR suggests that a higher rate of removal of calcium, either from the myofilaments or from the cytoplasm, may be an important factor in causing the changes in SHR soleus. The faster relaxation may be compared with a similar change reported in SHR cardiac myocytes.

Properties of the fluorescent sodium indicator "SBFI" in rat and rabbit cardiac myocytes.

INTRODUCTION: Although some properties of the fluorescent sodium indicator "SBFI" are known, there is no accepted method by which the SBFI signal might be calibrated for intracellular Na (Nai) in cardiac cells. The first aim of this study was to characterize the loading and compartmentalization of this indicator in single cardiac myocytes. The second aim was, from experimental observation, to develop a rational calibration method for SBFI. The third aim was to use this Na indicator to study the dependence of tonic contraction on Nai in voltage-clamped ventricular myocytes. METHODS AND RESULTS: SBFI was incorporated into myocytes by incubating with the acetoxymethyl ester (10 microM) for 2 hours. This led to an intracellular concentration of SBFI free acid of 122 +/- 17 microM. We considered a number of issues with respect to compartmentalization of indicator and, under our conditions, we found the majority (71%) of indicator was situated in the cytoplasm. Therefore, SBFI indicates mainly changes of cytoplasmic Na. Calibration of the indicator for Nai was performed by equilibrating internal and external Na. We investigated the conditions required for optimum transmembrane Na equilibration and found it necessary to use a calibration solution free of both Ca and magnesium (Mg). The Na ionophores gramicidin D and monensin were both required, and it was also necessary to inhibit the Na/K pump for optimum Na equilibration. Using these conditions, the Nai concentration in quiescent rat ventricular myocytes was 10.9 +/- 0.74 mM (mean +/- SEM, n = 40; equivalent to an Na activity of 8.3 mM). The concentration of Nai was significantly lower in quiescent rabbit myocytes: 3.8 +/- 0.23 mM (n = 24; equivalent to an Na activity of 2.9 mM). In voltage-clamped rabbit myocytes, inhibition of the Na/K pump caused a rise of Nai; there were also marked effects on the tonic shortening elicited by ramp depolarizations. As Nai rose, the magnitude of tonic shortening increased and its voltage dependence also changed. CONCLUSION: These results confirm the suitability of SBFI for measuring Nai in cardiac cells. Provided that steps are taken to optimize transmembrane Na equilibration, the indicator can be calibrated for Nai. The different Nai of rat and rabbit myocytes has implications for the function of sarcolemmal Na/Ca exchange in each cell type. An Nai of 10.9 mM in rat myocytes gives a calculated reversal potential for the exchange of -35 mV. In comparison, an Nai of 3.8 mM in rabbit myocytes leads to a reversal potential for the exchange +45 mV. Therefore, relatively small changes of Nai can shift the reversal potential of the exchange to values that are substantially more positive or negative than zero. The behavior of voltage-dependent tonic contraction in rabbit myocytes was consistent with the Na/Ca exchange reversal potential being more positive than zero in these cells.

Intracellular calcium transients recorded with Fura-2 in spontaneously active myocytes isolated from the atrioventricular node of the rabbit heart.

We have used the fluorescent Ca indicator Fura-2 to assess the changes in intracellular calcium (Cai) in single spontaneously active myocytes isolated from the rabbit atrioventricular node (AVN). Simultaneous recordings of membrane potential and the Fura-2 ratio signal (which reflects Cai) showed that a transient rise of Cai occurred with each spontaneous action potential (AP). The AP upstroke preceded the rise in Cai and repolarization of the AP occurred faster than the decline of Cai. The level of Cai remained raised and progressively declined towards a baseline diastolic level during the subsequent pacemaker depolarization. The Fura-2 (Cai) transient in spontaneously active AVN cells had a time-to-peak of 49.2 +/- 5.4 ms (mean +/- s.e.m.; n = 7) and declined with a single exponential time course (time constant = 139.8 +/- 23.9 ms; n = 7). Application of 10 microM ryanodine completely and irreversibly abolished the Cai transient, identifying the sarcoplasmic reticulum (SR) as the major source of releasable Ca. Both removal of external Ca and block of L-type Ca channels (with 2 microM nifedipine) also abolished Cai transients, suggesting that Ca entry via L-type Ca-channels is involved in triggering the SR Ca release underlying the Cai transient. Removal of external Na (in the presence of 20 microM nifedipine to block L-type Ca channels) caused a reversible increase in Cai, showing that Na/Ca exchange is present in AVN cells and that it is involved in Cai regulation. Spontaneous Cai transients were abolished by 1 microM acetylcholine, and this was associated with a hyperpolarization of membrane potential and cessation of action potentials.(ABSTRACT TRUNCATED AT 250 WORDS)

One hump or two? The triggering of calcium release from the sarcoplasmic reticulum and the voltage dependence of contraction in mammalian cardiac muscle.

We have examined the hypothesis that the sarcolemmal Na/Ca exchanger is able to trigger calcium release from the sarcoplasmic reticulum in a direct fashion. We propose that when the cardiac muscle membrane is depolarised, for instance during the upstroke of the action potential or a square voltage clamp pulse, the voltage dependent Na/Ca exchanger generates an initial "spike" of calcium entry which is sufficient to trigger a fraction of the normal sarcoplasmic reticular calcium release, via calcium induced calcium release. For the last 20 years, it has been widely considered that calcium entry through L-type calcium channels is the only trigger for calcium release from sarcoplasmic reticulum in cardiac muscle. In the first section of this review, we examined some of the earlier studies of excitation-contraction coupling which used multicellular preparations of cardiac muscle. We suggested that these earlier studies do not support the idea that calcium entry via the calcium current (ICa) is the only trigger for sarcoplasmic reticular release. In contrast, more recent studies using isolated myocytes have supported ICa as the only trigger. However, these were performed mostly with a low or absent sodium inside the cell, or with an increased intracellular calcium buffering, or with other altered internal ions (eg, high magnesium or caesium in the pipette) or at a relatively low temperature. All these factors may have reduced or abolished the initial spike of calcium entry which the Na/Ca exchanger is expected to generate at the start of depolarisation. New studies on myocytes are presented, using conditions where cells are dialysed minimally, or where a normal level of internal sodium is preserved deliberately.(ABSTRACT TRUNCATED AT 250 WORDS)

A role for depolarisation induced calcium entry on the Na-Ca exchange in triggering intracellular calcium release and contraction in rat ventricular myocytes.

OBJECTIVE: The aim was to test whether depolarisation-induced calcium entry on the Na-Ca exchange is able to trigger calcium release from the sarcoplasmic reticulum in rat ventricular myocytes. METHODS: Myocytes were isolated enzymatically from the left ventricle of the rat heart. Cells were impaled with narrow tipped microelectrodes to minimise intracellular dialysis and maintain normal internal ionic conditions. Cells were voltage clamped, contraction was measured optically, and in some experiments intracellular calcium was measured with Fura-2. RESULTS: When the fast Na current was inactivated by using a holding potential of -40 mV, Ca entry via L-type Ca channels was expected to be the only mechanism capable of triggering sarcoplasmic reticular Ca release. In this situation, blocking L-type Ca channels should have abolished sarcoplasmic reticular release and the phasic twitch. However, after 2 min exposure to 20 microM nifedipine, which abolished the Ca current (ICa) completely, voltage clamp depolarisation from -40 mV to 0 mV still elicited 41(SEM 8.9)% of the control phasic twitch (n = 22 cells). This shows that there must be another mechanism, besides Ca entry via Ca channels, by which membrane depolarisation can trigger sarcoplasmic reticular release and the phasic twitch. The phasic twitch that remained in the presence of nifedipine increased progressively with the magnitude of step depolarisation, required a functional sarcoplasmic reticulum, was abolished by 5 mM external nickel, and was sensitive to both the Na and Ca transmembrane gradients. CONCLUSIONS: The voltage dependent sarcolemmal Na-Ca exchange is predicted theoretically to generate a transient Ca entry at the start of a step membrane depolarisation, when membrane potential suddenly becomes more positive than the reversal potential of the Na-Ca exchange. The results of this study indicate that in rat myocytes with normal internal ions, physiological levels of membrane depolarisation generate a sufficient Ca entry on the exchange to trigger sarcoplasmic reticular calcium release and contraction. In the absence of ICa, this mechanism is capable of triggering a calcium release which leads to about 40% of the phasic contraction in cells depolarised from -40 mV to 0 mV. The existence of this sarcoplasmic triggering mechanism may have significance for the normal control of cardiac muscle contraction.

Investigation of the mechanisms underlying the increased contraction of hypertrophied ventricular myocytes isolated from the spontaneously hypertensive rat.

OBJECTIVE: The aim was to investigate the cellular mechanisms responsible for the increased contraction of left ventricular myocytes isolated from the spontaneously hypertensive rat (SHR). METHODS: Single myocytes were isolated enzymatically from the left ventricles of SHR, Wistar-Kyoto (WKY), and Wistar rats. WKY and Wistar myocytes were used as normotensive controls. Cytoplasmic calcium was measured with Fura-2 and contraction was measured optically. Membrane potential was measured with microelectrodes and cells were voltage clamped to measure the amplitude of L-type calcium current (iCa). RESULTS: Under action potential conditions, SHR myocytes had a larger calcium transient and an increased sarcoplasmic reticular calcium content compared to normotensive myocytes. There was no detectable difference in the resting cytoplasmic calcium concentration between SHR and control myocytes. SHR myocytes also had a prolonged action potential compared to normotensive cells. However, when cells were voltage clamped and short pulses of 120 ms duration were applied (a similar duration of depolarisation to the action potential), the difference in the calcium transient or contraction between SHR and normotensive myocytes was abolished. SHR myocytes had an unchanged amplitude of ICa in comparison to control myocytes, and there was no detectable difference in the myofilament response to calcium between SHR and control myocytes. CONCLUSIONS: (1) Hypertrophied SHR myocytes stimulated with action potentials had an increased calcium transient compared to normotensive cells. The greater calcium transient in the SHR cells is likely to be a major factor responsible for their increased contraction. (2) SHR myocytes had a prolonged action potential in comparison to normotensive cells. (3) The amplitude of ICa and myofilament response to calcium were unchanged in SHR myocytes, suggesting that these factors do not play a role in the increased contraction of these cells. (4) Since the difference between SHR and control cells was abolished by voltage clamping the cells to prevent the difference of action potential, it is unlikely that an alteration of intrinsic mechanisms in SHR myocytes is responsible for their increased contraction. Rather, it suggests that the prolonged action potential of SHR myocytes plays a important role in causing their increased calcium transient and contraction. Our results indicate that the prolonged action potential in SHR cells results in an increased calcium content of the sarcoplasmic reticulum, which leads to a greater sarcoplasmic reticular calcium release upon stimulation and an increased contraction.

The electrophysiological characteristics of hypertrophied ventricular myocytes from the spontaneously hypertensive rat.

OBJECTIVE: Previous studies on multicellular preparations have shown that hypertrophied cardiac muscle from the spontaneously hypertensive rat (SHR) has a prolonged action potential. The first aim of the present study was to determine whether the action potential of isolated left ventricular myocytes was similarly prolonged and to study the underlying membrane currents that might be responsible. The second aim was to evaluate the L-type calcium current amplitude of SHR myocytes, as we have recently shown that they have an increased contraction and an increase in the calcium trigger entering via the L-type calcium channel might be one possible mechanism for this. METHODS: The electrophysiological characteristics of left ventricular myocytes isolated from the SHR were compared with those from normotensive control rats. Action potentials were recorded with microelectrodes. Cells were voltage-clamped and the membrane currents elicited by steps to different potentials were analysed. Blockers of potassium and calcium currents were used to reveal the contribution made by these currents to net membrane currents. RESULTS: SHR myocytes had prolonged action potentials. The action potential duration of SHR myocytes at 90% repolarization was found to be longer, although at 20% and 50% repolarization no difference was found. There was no difference in the resting membrane potential between SHR and control myocytes. Using a voltage clamp we studied the L-type calcium current and potassium currents. The major change in SHR myocytes was a decrease in the magnitude (normalized to the membrane capacitance) of the inward rectifier potassium current elicited by negative potentials. There was no detectable difference in either the transient outward or delayed rectifier potassium currents. We also found no difference in the magnitude, time course or voltage dependence of L-type calcium current in hypertrophied SHR myocytes. CONCLUSIONS: First, the action potential of SHR myocytes was prolonged compared with control myocytes. Secondly, the main change in SHR myocytes was that pulses to negative potentials elicited a lower inward rectifier potassium current. A reduction in the density of inward rectifier channels might play a role in prolonging the SHR action potential, since a lower outward repolarizing current will flow through inward rectifier potassium channels during the SHR action potential repolarization. Thirdly, there was no difference in L-type calcium current density or time course between SHR and control myocytes. Thus, a change in L-type calcium current probably plays no role in causing the prolonged SHR action potential or the increased contraction of hypertrophied SHR ventricular myocytes. Finally, the prolonged action potential in SHR myocytes may itself be one factor responsible for the increased contraction of these cells.

Use of thrombolysis for acute myocardial infarction by general practitioners.

The early administration of thrombolytic agents significantly reduces mortality following a myocardial infarct and ideally they could be given by general practitioners when the patient is first seen. However, the diagnosis of myocardial infarction in the early stages can be very difficult especially if an electrocardiogram is not available. This may limit the use of thrombolytic drugs by general practitioners. We assessed the accuracy of diagnosis in general practice by asking general practitioners referring patients with chest pain, the likelihood that the event was due to a myocardial infarction and if they would use thrombolysis if it were available. Diagnostic accuracy and appropriate use of thrombolysis was analysed retrospectively, comparing the general practitioner with the admitting hospital doctor. One hundred consecutive patients were studied. The general practitioners accurately diagnosed myocardial infarctions in approximately 45% of cases and would have given thrombolysis inappropriately on 67% of occasions mainly because the final diagnosis in most of these patients was unstable angina rather than infarction. The hospital doctors administered streptokinase inappropriately to 33% of the patients and four had complications during treatment. Of those patients receiving thrombolysis, the average time delay from the general practitioner referring the patient to hospital to the patient being treated was 107 minutes. This study confirms that the diagnosis of myocardial infarction in the early stages is difficult and that thrombolytic therapy may be given inappropriately (mainly to patients with unstable angina). We conclude that until the accuracy of diagnosis of myocardial infarction can be improved in general practice it would seem inappropriate for thrombolysis to be given in the community at the moment.

Contractile properties of ventricular myocytes isolated from spontaneously hypertensive rat.

OBJECTIVE: To determine whether there are any differences in contractile properties of individual cardiac myocytes isolated from the spontaneously hypertensive rat (SHR) in comparison with its normotensive control--the Wistar-Kyoto (WKY) rat. DESIGN: The effects of cardiac hypertrophy upon individual myocytes from SHR have not been studied previously. Isolated cardiac myocytes do not suffer from a number of problems inherent in experiments on multicellular preparations. METHODS: Seven SHR and eight WKY animals were studied. Age-matched animals were compared at 60 and 100 days old. Ventricular myocytes were isolated enzymatically. Myocyte length and width was measured. The cells were stimulated with extracellular electrodes and contraction was measured optically. The effects of altering stimulus rate and extracellular calcium concentration upon contraction were studied. RESULTS: SHR myocytes were found to be significantly wider than WKY myocytes. The contraction (i.e. unloaded cell shortening) of SHR myocytes at stimulation rate of 0.3, 1, 2 and 3 Hz was significantly increased. The time-course of contraction was altered, with SHR myocytes having an increased maximal velocity of shortening and relaxation. The response to changes in bathing calcium was similar in both strains. CONCLUSIONS: Individual cardiac myocytes isolated from SHR have an increased contraction. This indicates that cardiac hypertrophy, at least in the early stages, is a protective adaptation allowing the heart to overcome the increased afterload resulting from hypertension.

Epidural spinal electrical stimulation for severe angina: a study of its effects on symptoms, exercise tolerance and degree of ischaemia.

The effectiveness of epidural spinal electrical stimulation has been studied in 14 patients with severe intractable angina unresponsive to standard therapies including bypass grafting. After implantation of the neurostimulator units the patients were assessed by a symptom questionnaire, treadmill exercise testing and right atrial pacing. There was a significant improvement of symptoms and GTN consumption fell markedly. With the neurostimulator on, exercise duration increased from a mean (CI) of 414 (153) to 478 (149) s, and total ST segment depression was less both at maximum exercise (7.1 (4.5) vs 5.6 (4.2) mm) and at 90% of the maximum control heart rate (3.5 (3.7) vs 2.6 (4.3) mm), with similar rate-pressure product at maximum exercise. With right atrial pacing the maximum heart rate reached before onset of angina was increased (143 (14) to 150 (7) b.min-1) and total ST segment depression was less at all heart rates. Benefit has persisted in some patients for over 2 years without any apparent adverse sequelae. Epidural spinal electrical stimulation is, therefore, an alternative therapy for some patients with intractable angina which has not responded to standard therapies.

The effects of short-term voluntary immobilization on the contractile properties of the human triceps surae.

In four male subjects one leg was immobilized in a full leg cast for 2 weeks. Measurements of the contractile properties of both triceps surae were made before, during and after immobilization. There was a significant increase in the mean twitch time to peak tension (Tc) after 1 week of immobilization from 126 +/- 10 ms to 143 +/- 20 ms (P less than 0.05) and in the half-relaxation time (T1/2r) from 88 +/- 7 ms to 107 +/- 12 ms (P less than 0.01). There were no further significant (P less than 0.1) changes in the twitch characteristics during the second week of immobilization. The strength of a maximal voluntary contraction (m.v.c.) declined by 11% (P less than 0.05) after 1 week and 24% (P less than 0.05) after 2 weeks. Twitch tension, tetanic tension and muscle fatigability were not significantly altered during immobilization. Muscle (plus bone) calf cross-sectional area (A) was reduced by 5% (P less than 0.01) after 1 week and a further 3% (P less than 0.05) after 2 weeks. The Tc and T1/2r of the twitch, m.v.c. and A returned to control values within 2, 7, 4 and 14 d respectively. No significant (P less than 0.01) changes were observed in the mechanical properties of the triceps surae of the contralateral limb during the period of immobilization. The results suggest that short-term voluntary immobilization is associated with atrophy and a diminished capacity of the muscle to develop maximal voluntary force.(ABSTRACT TRUNCATED AT 250 WORDS)