From static micrographs to particle aggregation dynamics in three dimensions.

Studies on colloidal aggregation have brought forth theories on stability of colloidal gels and models for aggregation dynamics. Still, a complete link between developed frameworks and obtained laboratory observations has to be found. In this work, aggregates of silica nanoparticles (20 nm) are studied using diffusion limited cluster aggregation (DLCA) and reaction limited cluster aggregation (RLCA) models. These processes are driven by the probability of particles to aggregate upon collision. This probability of aggregation is one in the DLCA and close to zero in the RLCA process. We show how to study the probability of aggregation from static micrographs on the example of a silica nanoparticle gel at 9 wt%. The analysis includes common summary functions from spatial statistics, namely the empty space function and Ripley's K-function, as well as two newly developed summary functions for cluster analysis based on graph theory. One of the new cluster analysis functions is related to the clustering coefficient in communication networks and the other to the size of a cluster. All four topological summary statistics are used to quantitatively compare in plots and in a least-square approach experimental data to cluster aggregation simulations with decreasing probabilities of aggregation. We study scanning transmission electron micrographs and utilize the intensity-mass thickness relation present in such images to create comparable micrographs from three-dimensional simulations. Finally, a characterization of colloidal silica aggregates and simulated structures is obtained, which allows for an evaluation of the cluster aggregation process for different aggregation scenarios. As a result, we find that the RLCA process fits the experimental data better than the DLCA process.

Estimation of mass thickness response of embedded aggregated silica nanospheres from high angle annular dark-field scanning transmission electron micrographs.

In this study, we investigate the functional behaviour of the intensity in high-angle annular dark field scanning transmission electron micrograph images. The model material is a silica particle (20 nm) gel at 5 wt%. By assuming that the intensity response is monotonically increasing with increasing mass thickness of silica, an estimate of the functional form is calculated using a maximum likelihood approach. We conclude that a linear functional form of the intensity provides a fair estimate but that a power function is significantly better for estimating the amount of silica in the z-direction. The work adds to the development of quantifying material properties from electron micrographs, especially in the field of tomography methods and three-dimensional quantitative structural characterization from a scanning transmission electron micrograph. It also provides means for direct three-dimensional quantitative structural characterization from a scanning transmission electron micrograph.

TMD before and after correction of dentofacial deformities by orthodontic and orthognathic treatment.

The aims of the study were to investigate the alteration of temporomandibular disorders (TMD) after correction of dentofacial deformities by orthodontic treatment in conjunction with orthognathic surgery; and to compare the frequency of TMD in patients with dentofacial deformities with an age and gender matched control group. TMD were evaluated in 121 consecutive patients (treatment group), referred for orthognathic surgery, by a questionnaire and a clinical examination. 18 months after treatment, 81% of the patients completed a follow-up examination. The control group comprised 56 age and gender matched subjects, of whom 68% presented for follow-up examination. TMD were diagnosed according to research diagnostic criteria for TMD. At baseline examination, the treatment group had a higher frequency of myofascial pain (P=.035) and arthralgia (P=.040) than the control group. At follow-up, the frequencies of myofascial pain, arthralgia and disc displacement had decreased in the treatment group (P=.050, P=.004, P=.041, respectively). The frequency of TMD was comparable in the two groups at follow-up. Patients with dentofacial deformities, corrected by orthodontic treatment in conjunction with orthognathic surgery, seem to have a positive treatment outcome in respect of TMD pain.

MADSTRESS: a linear approach for evaluating scattering and absorption coefficients of samples measured using time-resolved spectroscopy in reflection.

Time-resolved spectroscopy is a powerful technique permitting the separation of the scattering properties from the chemical absorption properties of a sample. The reduced scattering coefficient and the absorption coefficient are usually obtained by fitting diffusion or Monte Carlo models to the measured data using numerical optimization techniques. However, these methods do not take the spectral dimension of the data into account during the evaluation procedure, but evaluate each wavelength separately. A procedure involving multivariate methods may seem more appealing for people used to handling conventional near-infrared data. In this study we present a new method for processing TRS spectra in order to compute the absorption and reduced scattering coefficients. This approach, MADSTRESS, is based on linear regression and a two-dimensional (2D) interpolation procedure. The method has allowed us to calculate absorption and scattering coefficients of apples and fructose powder. The accuracy of the method was good enough to provide the identification of fructose absorption peaks in apple absorption spectra and the construction of a calibration model predicting the sugar content of apples.

Potassium and calcium current blocking properties of the novel antiarrhythmic agent H 345/52: implications for proarrhythmic potential.

OBJECTIVES: To study the blocking effects of H 345/52 on ionic currents of rabbit ventricular myocytes and how these features translate into a proarrhythmic potential. METHODS: The single electrode voltage clamp technique was used to study the effects of H 345/52 on the rapid component of the delayed rectifying potassium current, I(Kr), and the L-type calcium current (I(Ca)). Differential effects of H 345/52 and almokalant on APD prolongation were studied in a rabbit Purkinje fibre/ventricular muscle preparation. The temporal variability of the action potential duration (APD) and its relation to proarrhythmias was examined in Langendorff-perfused rabbit hearts administered H 345/52 or almokalant. Anaesthetised, methoxamine-sensitised rabbits were used to assess the propensity of intravenous H 345/52 and ibutilide to induce torsades de pointes (TdP). RESULTS: H 345/52 potently blocked I(Kr) (IC(50)=40 nM) without consequential use-dependency. The I(Ca) was also blocked, but at higher concentrations (IC(50)=1.3 microM). Block of I(Ca) was markedly frequency-dependent (positive) and influenced by membrane potential, such that H 345/52 was more effective following clamp steps from plateau potentials than from -80 mV. In the Purkinje fibre-ventricular muscle preparation, almokalant prolonged the Purkinje fibre APD preferentially, whereas H 345/52 homogeneously prolonged APD in both tissue types. In the perfused rabbit heart, H 345/52 (1 microM) and almokalant (0.3 microM) prolonged APD to a similar degree but increased the temporal variability of APD differently, from 3+/-0.4 ms in control hearts to 8+/-1.2 ms and to 38+/-7.5 ms (P<0.001 vs. H 345/52), respectively. Unequivocal early after-depolarisations were seen in 5/6 almokalant-perfused hearts but in no heart administered H 345/52 (P<0.05). In anaesthetised rabbits, H 345/52 (17.4 micromol/kg) or ibutilide (2.6 micromol/kg maximum), maximally lengthened the QT interval from 133+/-4.5 to 177+/-8.0 ms and from 125+/-5.1 to 166+/-9.3 ms (P<0.001, n=8). However, whereas ibutilide induced TdP in all animals at 0.06+/-0.009 micromol/kg, H 345/52 did not induce TdP (P=0.0002) at up to 17.4 micromol/kg. CONCLUSIONS: H 345/52 blocks I(Kr) with high potency and I(Ca) with somewhat lower potency and was found to delay ventricular repolarisation without substantially increasing temporal or spatial dispersion and without inducing early after-depolarisations or TdP.

Neuropeptide Y1- and Y2-receptor-mediated cardiovascular effects in the anesthetized guinea pig, rat, and rabbit.

Neuropeptide Y (NPY) causes vasoconstriction through Y1-receptors and inhibits vagal bradycardia through presynaptic Y2-receptors. These effects of NPY were investigated in anesthetized guinea pigs, rats, and rabbits to find the most suitable species for evaluation of Y1- and Y2-active agents in vivo. The increase in blood pressure (through Y1) of lower doses of NPY was similar in the three species (ED50, 0.9 +/- 0.13, 0.8 +/- 0.39, and 0.6 +/- 0.09 nmol/kg, respectively), but higher doses had depressor effects in four of six rats. Vagal bradycardia, induced by electrical stimulation of the right cervical vagus nerve, was inhibited by NPY in the guinea pig and in the rat (ED35, 3.5 +/- 0.46 and 11.2 +/- 1.79 nmol/kg, respectively; p < 0.05) but not in the rabbit. In the guinea pig, the Y2-receptor-preferring fragment NPY(3-36) and the selective Y1-receptor antagonist H 409/22 were used to confirm that the increase in blood pressure was mediated solely through the Y1-receptor and the vagal inhibition solely through the Y2-receptor. Aside from the cardiovascular effects, NPY caused a decrease in the body temperature and inhibited vagal bronchoconstriction in this species. Considering that NPY may cause depressor effects in the rat and has no effect on the vagal bradycardia in the rabbit, the guinea pig is preferable to both these species for assessment of Y1- and Y2-receptor-active agents in vivo.

Post-conflict affiliation in common marmosets (Callithrix jacchus jacchus).

Post-conflict (PC) affiliation has been demonstrated in a number of Old World monkeys and apes, but very little is known about the occurrence of the phenomenon in New World monkeys. This study examined 282 PC interactions after spontaneous conflicts around feeding time in two family groups (N = 12) of captive common marmosets, Callithrix jacchus jacchus. We found an overall corrected conciliatory tendency of 31%. Selective attraction was seen: former opponents met significantly more often in PCs than in matched controls (MCs) (27% and 16%, respectively). There was no difference in the occurrence of PC affiliation between dyads consisting of parent-offspring constellations compared to offspring-offspring constellations. PC affiliative behaviors were seen in the first three minutes following conflict termination, and consisted mainly of proximity, play invitations, and food transfer. Notably, former opponents remained within arm's reach after 17% of conflicts. Affiliation was more likely to follow after conflicts involving play issues. The functional importance of the PC affiliation in marmosets remains to be examined.

Lidocaine and nisoldipine attenuate almokalant-induced dispersion of repolarization and early afterdepolarizations in vitro.

INTRODUCTION: Treatment with Class III antiarrhythmic agents may lead to increased dispersion of repolarization and early afterdepolarizations (EADs), which are both likely substrates for torsades de pointes. Recent studies in vivo have shown that the prevalence of proarrhythmias induced by Class III agents may be reduced by Na(+)- or Ca(2+)-blocking agents. In the present study, tentative mechanisms for this protective effect were investigated in vitro. METHODS AND RESULTS: Transmembrane action potentials were recorded simultaneously from rabbit isolated ventricular muscle (VM) and Purkinje fibers (PF). At a basic cycle length (BCL) of 500 msec, the Class III agent almokalant (0.1 microM) increased the dispersion by prolonging the action potential duration (APD) significantly more in the PF (33% +/- 4.2%, n = 18) than in the VM (17% +/- 5.9%, n = 18, P < 0.05). In six of the preparations, addition of 1, 5, and 25 microM lidocaine reduced the almokalant-induced prolongation in a concentration-dependent manner mainly in the PF, thereby decreasing the dispersion. At 5 microM lidocaine, the remaining prolongation was 7% +/- 12.2% (P < 0.05 vs time controls) in the PF and 14% +/- 6.4% in the VM, respectively. In six other preparations, the addition of 0.01, 0.05, and 0.25 microM nisoldipine did not reduce the almokalant-induced prolongation in the PF and VM, but attenuated the spike-and-dome appearance of the action potential in the PF. In separate experiments performed at a BCL of 1000 msec, EADs developed in 2 of 6 and 5 of 6 PF during superfusion with almokalant (0.3 and 1 microM, respectively) at an APD of 828 +/- 41.4 msec. In six separate preparations pretreated with lidocaine (5 microM), the almokalant-induced prolongation in the PF was less pronounced and EADs were not observed. Pretreatment with nisoldipine (0.05 microM) did not influence the response to almokalant, and in 4 of 6 preparations the APD exceeded 1000 msec. Despite this extensive prolongation, EADs did not appear. CONCLUSION: At concentrations that did not affect the APD in the VM but reduced the APD in the PF, lidocaine suppressed almokalant-induced dispersion and the development of EADs. Nisoldipine, on the other hand, inhibited almokalant-induced EADs directly. Hence, the primary APD-prolonging effect of a Class III agent may be preserved, but the risk of proarrhythmias reduced, during concomitant treatment with low concentrations of a Na(+)- or Ca(2+)-blocking agent.

Induction of rhythm abnormalities in the fetal rat heart. A tentative mechanism for the embryotoxic effect of the class III antiarrhythmic agent almokalant.

OBJECTIVES: The aim was to test the hypothesis that the recently reported embryotoxic effect of class III antiarrhythmic agents may be a result of electrophysiological disturbances induced by these agents. METHODS: Comparative studies of drug effects in the adult and fetal rat were performed using three experimental models: (1) effects of almokalant upon pregnancy and fetal mortality in rats given daily doses of 0, 10, 50, 100, or 400 mumol.kg-1 orally in the diet on days 6-15 of pregnancy; (2) effects of d-sotalol (1-1000 microM), almokalant (0.1-100 microM) and dofetilide (0.01-10 microM) on the adult and fetal cardiac action potential in vitro; (3) voltage clamp recordings in single fetal and adult ventricular myocytes superfused with almokalant (0.5 microM). RESULTS: In the groups of rats treated with 100 and 400 mumol.kg-1, respectively, the body weight gain was decreased from day 12 of gestation, and there were no viable fetuses at termination of pregnancy. In atrial as well as ventricular tissue, the class III agents induced a concentration dependent prolongation of the fetal action potential duration, accompanied by a reduction in heart rate and eventually the appearance of rhythm abnormalities and/or early afterdepolarisations. The adult action potential duration remained unaffected. An almokalant sensitive current (probably the delayed rectifier, IK) could be evoked both in the fetal and in the adult ventricular cells. CONCLUSIONS: Class III antiarrhythmic agents were shown to induce fetal mortality and rhythm abnormalities in the rat heart. Although they do not prove a causal relationship between these effects, our observations may have implications for the clinical use of class III antiarrhythmic agents in women of childbearing potential.

Proarrhythmic effects of the class III agent almokalant: importance of infusion rate, QT dispersion, and early afterdepolarisations.

OBJECTIVE: The aim was to study factors contributing to torsade de pointes in the acquired long QT syndrome. METHODS: Anaesthetised rabbits or cats were given a continuous infusion of methoxamine and the class III agent almokalant (at a rate of 5 or 25 nmol.kg-1.min-1, respectively) and the effects on incidence of torsade de pointes and QT dispersion were examined. Effects of almokalant on action potentials recorded from Purkinje fibres and ventricular cells of rabbits and cats were also studied. RESULTS: "High rate" infusion of almokalant prolonged the QTc interval [from 162(SEM 6.2) ms to 211 (5.3) ms, p < 0.001] and initiated torsade de pointes in 9/10 rabbits after a dose of 391(116.3) nmol.kg-1. During "low rate" infusion, 1/8 rabbits developed torsade de pointes (p = 0.0029) despite infusion of 900 nmol.kg-1 almokalant and QTc prolongation from 162(3.6) ms to 230(12.6) ms (p < 0.01). In eight separate rabbits given the high rate infusion of almokalant, seven developed torsade de pointes and the QTc dispersion increased from 15(1.7) ms to 32(5.6) ms (p < 0.05). In six rabbits given the low rate infusion, none developed torsade de pointes (p = 0.0023), and the QTc dispersion was unaltered. In six cats, high rate infusion induced a QT interval lengthening from 241(6.0) ms to 349(8.0) ms (p < 0.001), but in only one cat was torsade de pointes initiated and preceded by a marked increase in QT dispersion (from 22 ms to 78 ms). In vitro, almokalant caused a marked lengthening of the action potential duration and early afterdepolarisations in Purkinje fibres but not in ventricular muscle cells of the rabbit. In the cat, however, almokalant induced a homogeneous prolongation of the action potential duration in both cell types, and early afterdepolarisations were never observed. CONCLUSIONS: The rate of infusion of repolarisation delaying agents may influence the dispersion of repolarisation and play a decisive role in the initiation of torsade de pointes.

Electrophysiological and inotropic effects of H 234/09 (almokalant) in vitro: a comparison with two other novel IK blocking drugs, UK-68,798 (dofetilide) and E-4031.

OBJECTIVE: The aim was to compare the electrophysiological and inotropic effects of the novel class III agents H 234/09, UK-68,798, and E-4031 in vitro. METHODS: The electrophysiological effects were investigated by recording transmembrane action potentials in the isolated ventricular muscle and Purkinje fibres of the rabbit; effects on force (adjusted to the maximum isoprenaline response) and refractoriness were investigated in the isolated cat papillary muscle. RESULTS: It was shown that all the drugs induced a concentration dependent prolongation of the action potential duration, which was much more pronounced in the Purkinje fibres than in the ventricular muscle. However, when compared at concentrations giving a 15% increase of the action potential duration in ventricular muscle, H 234/09 was significantly less effective in the Purkinje fibres than the other two drugs. In the cat papillary muscle all drugs induced an increase in force development. This increase tended to parallel the increase in effective refractory period. However, at prolongations of effective refractory period of more than approximately 50% the increase in developed force levelled off. CONCLUSIONS: All the class III agents investigated showed a positive inotropic effect, which may be of advantage when compared to conventional class I antiarrhythmic agents, which have cardiodepressant actions. Compared to UK-68,798 and E-4031, H 234/09 showed a less unfavourable profile in terms of dispersion of repolarisation, which theoretically may reduce the risk of arrhythmias associated with delayed repolarisation. However, this less unfavourable profile must, like the positive inotropic effect, ultimately be investigated in clinical trials.

Antiarrhythmic effects of potassium channel openers in rhythm abnormalities related to delayed repolarization.

BACKGROUND: Earlier observations have indicated that repolarization-delaying agents may, under certain circumstances, have the propensity to induce polymorphous ventricular tachyarrhythmias (PVTs) (i.e., torsade de pointes). We have studied whether the potassium channel opener pinacidil and two of its pyridylcyanoguanidine analogues (P1075 and P1188) have any antiarrhythmic effects on clofilium-induced PVTs and triggered responses in rabbits in vivo and in vitro. METHODS AND RESULTS: Anesthetized rabbits were pretreated with propranolol (2 mumol/kg i.v.) and subsequently given a concomitant intravenous infusion of clofilium (63 nmol/kg/min for maximally 15 minutes) and the alpha 1-agonist methoxamine (70 nmol/kg/min). In vehicle-pretreated rabbits (n = 19), clofilium invariably induced PVTs, which closely resembled torsade de pointes and were preceded by a marked prolongation of the QTU interval (27 +/- 2.4%, p less than 0.001). In a separate group of seven rabbits in which monophasic action potentials were recorded from the left ventricular endocardium, the tachyarrhythmia was preceded by deflections consistent with early afterdepolarizations (EADs) of the plateau repolarization phase of the monophasic action potentials. Intravenous administration of the pyridylcyanoguanidines in doses reducing mean arterial blood pressure by 25 or 50 mm Hg, respectively, was associated with a dose-dependent attenuation in the occurrence of clofilium-induced PVTs. In the pinacidil-pretreated rabbits (0.41 mumol/kg or 1.86 mumol/kg i.v.), the occurrence of PVTs was reduced from seven of seven rabbits to five of six and to three of seven rabbits (p = 0.035 versus vehicle-pretreated controls), respectively. In rabbits pretreated with the low dose of P1075 (0.01 mumol/kg i.v.), PVT occurrence was reduced from six of six rabbits to two of six rabbits (p = 0.030), whereas in six rabbits given the high dose of P1075 (0.13 mumol/kg), no PVTs appeared (p = 0.001). When the sulfonylurea glibenclamide (10 mumol/kg i.v.) was administered to rabbits before P1075 (0.13 mumol/kg) was infused, clofilium induced PVTs in five of six rabbits (not significantly different from the incidence in the vehicle-pretreated rabbits). Pretreatment with P1188 (4.36 mumol/kg or 11.88 mumol/kg i.v.) caused a reduction in the occurrence of PVT from six of six rabbits to five of six and to none of six rabbits (p = 0.001), respectively. In the six animals pretreated with the high dose of P1188 in which no clofilium-induced arrhythmias were elicited, glibenclamide (20 mumol/kg i.v.) was injected after the entire dose of clofilium had been administered. In these rabbits, premature ventricular systoles and PVTs appeared within a few minutes in five and four of the animals, respectively. In contrast to the pyridylcyanoguanidines, diltiazem pretreatment (0.9 mumol/kg i.v., decreasing arterial pressure by 50 mm Hg) did not attenuate PVT occurrence (five of six rabbits). Acute administration of P1075 (0.13 mumol/kg) during recurrent attacks of PVTs abruptly regularized the rhythm in 12 of 13 animals and diminished EADs observed in monophasic action potentials recorded from the left ventricular endocardium. In in vitro experiments, action potentials were simultaneously recorded from rabbit Purkinje fibers and ventricular muscle cells. Clofilium markedly prolonged action potential duration in Purkinje fibers but not in ventricular muscle cells, and eventually, bradycardia-dependent EADs and triggered activity were elicited. P1075 completely abolished EADs and triggered activity in all (six of six) experiments. Glibenclamide antagonized the suppressive effect of P1075; hence, EADs and triggered responses reappeared and resembled those present before P1075. CONCLUSIONS: These results suggest that ATP-sensitive potassium channel activat BACKGROUND: Earlier observations have indicated that repolarization-delaying agents may, under certain circumstances, have the propensity to induce polymorp

Prolonged action potential duration and positive inotropy induced by the novel class III antiarrhythmic agent H 234/09 (Almokalant) in isolated human ventricular muscle.

The electromechanical properties of H 234/09 (Almokalant), a novel class III antiarrhythmic agent, was examined in isolated human ventricular muscle strips excised from patients undergoing mitral valve replacement. Using transmembrane microelectrode recording techniques, we demonstrated that H 234/09 markedly prolonged the action potential duration (APD) without affecting the maximal rate of depolarization or action potential amplitude. At 75 and 90% repolarization APD was prolonged to a similar extent, whereas the lengthening at 50% repolarization was somewhat less marked. In isometrically contracting muscle strips, H 234/09 increased peak developed force and its maximal rate of rise (dF/dt) and fall (-dF/dt) in a concentration-dependent manner, whereas time to peak developed force was unaltered. We conclude from these studies that H 234/09 is a class III agent in human ventricular muscle and that the class III effect is linked with a positive inotropic response.