Diclofenac Prolongs Repolarization in Ventricular Muscle with Impaired Repolarization Reserve

Background: The aim of the present work was to characterize the electrophysiological effects of the non-steroidal anti- inflammatory drug diclofenac and to study the possible proarrhythmic potency of the drug in ventricular muscle. Methods: Ion currents were recorded using voltage clamp technique in canine single ventricular cells and action potentials were obtained from canine ventricular preparations using microelectrodes. The proarrhythmic potency of the drug was investigated in an anaesthetized rabbit proarrhythmia model. Results: Action potentials were slightly lengthened in ventricular muscle but were shortened in Purkinje fibers by diclofenac (20 mM). The maximum upstroke velocity was decreased in both preparations. Larger repolarization prolongation was observed when repolarization reserve was impaired by previous BaCl 2 application. Diclofenac (3 mg/kg) did not prolong while dofetilide (25 mg/kg) significantly lengthened the QT c interval in anaesthetized rabbits. The addition of diclofenac following reduction of repolarization reserve by dofetilide further prolonged QT c . Diclofenac alone did not induce Torsades de Pointes ventricular tachycardia (TdP) while TdP incidence following dofetilide was 20%. However, the combination of diclofenac and dofetilide significantly increased TdP incidence (62%). In single ventricular cells diclofenac (30 mM) decreased the amplitude of rapid (I Kr ) and slow (I Ks ) delayed rectifier currents thereby attenuating repolarization reserve. L-type calcium current (I Ca ) was slightly diminished, but the transient outward (I to ) and inward rectifier (I K1 ) potassium currents were not influenced. Conclusions: Diclofenac at therapeutic concentrations and even at high dose does not prolong repolarization markedly and does not increase the risk of arrhythmia in normal heart. However, high dose diclofenac treatment may lengthen repolarization and enhance proarrhythmic risk in hearts with reduced repolarization reserve

Ionic mechanisms limiting cardiac repolarization-reserve in humans compared to dogs.

The species-specific determinants of repolarization are poorly understood. This study compared the contribution of various currents to cardiac repolarization in canine and human ventricle. Conventional microelectrode, whole-cell patch-clamp, molecular biological and mathematical modelling techniques were used. Selective IKr block (50–100 nmol l−1 dofetilide) lengthened AP duration at 90% of repolarization (APD90) >3-fold more in human than dog, suggesting smaller repolarization reserve in humans. Selective IK1 block (10 μmol l−1 BaCl2) and IKs block (1 μmol l−1 HMR-1556) increased APD90 more in canine than human right ventricular papillary muscle. Ion current measurements in isolated cardiomyocytes showed that IK1 and IKs densities were 3- and 4.5-fold larger in dogs than humans, respectively. IKr density and kinetics were similar in human versus dog. ICa and Ito were respectively ∼30% larger and ∼29% smaller in human, and Na+–Ca2+ exchange current was comparable. Cardiac mRNA levels for the main IK1 ion channel subunit Kir2.1 and the IKs accessory subunit minK were significantly lower, but mRNA expression of ERG and KvLQT1 (IKr and IKsα-subunits) were not significantly different, in human versus dog. Immunostaining suggested lower Kir2.1 and minK, and higher KvLQT1 protein expression in human versus canine cardiomyocytes. IK1 and IKs inhibition increased the APD-prolonging effect of IKr block more in dog (by 56% and 49%, respectively) than human (34 and 16%), indicating that both currents contribute to increased repolarization reserve in the dog. A mathematical model incorporating observed human–canine ion current differences confirmed the role of IK1 and IKs in repolarization reserve differences. Thus, humans show greater repolarization-delaying effects of IKr block than dogs, because of lower repolarization reserve contributions from IK1 and IKs, emphasizing species-specific determinants of repolarization and the limitations of animal models for human disease

Pan-retinal characterisation of Light Responses from Ganglion Cells in the Developing Mouse Retina

International audienceWe have investigated the ontogeny of light-driven responses in mouse retinal ganglion cells (RGCs). Using a large-scale, high-density multielectrode array, we recorded from hundreds to thousands of RGCs simultaneously at pan-retinal level, including dorsal and ventral locations. Responses to di erent contrasts not only revealed a complex developmental pro le for ON, OFF and ON-OFF responses, but also unveiled di erences between dorsal and ventral RGC responses. At eye-opening, dorsal RGCs of all types were more responsive to light, perhaps indicating an environmental priority to nest viewing for pre-weaning pups. The developmental pro le of ON and OFF responses exhibited antagonistic behaviour, with the strongest ON responses shortly after eye-opening, followed by an increase in the strength of OFF responses later on. Further, we found that with maturation receptive eld (RF) center sizes decrease, spike-triggered averaged responses to white noise become stronger, and centers become more circular while maintaining di erences between RGC types. We conclude that the maturation of retinal functionality is not spatially homogeneous, likely re ecting ecological requirements that favour earlier maturation of the dorsal retina

Ground beetles from Sǎlaj county (Romania) (coleoptera: carabidae)

During a faunistical exploration of Sǎlaj county carried out in 2014 and 2015, 207 ground beetle (Carabidae) species were recorded from the area. Considering the earlier literature data the total number of carabid species known from the county is 246. Carabus variolosus Fabricius, 1787 is a Natura 2000 species, Pterostichus bielzii Fuss, 1878 is a species endemic to the Western Apuseni Mountains. Further rare species from the area: Dromius quadraticollis A. Morawitz, 1862, Elaphropus parvulus (Dejean, 1831), Lebia marginata (Geoffroy, 1785), Ophonus ardosiacus (Lučnik, 1922), Trechus amplicollis Fairmaire, 1859

Effect of diclofenac on action potential repolarization in canine right ventricular preparations with impaired repolarization reserve.

<p>(A) Representative superimposed action potentials recorded from canine right ventricular muscle preparation at cycle length of 1 s. In these experiments 30 µM BaCl₂ was applied to attenuate the repolarization reserve prior to 20 µM diclofenac superfusion. (B) Cycle length dependent changes in APD₉₀ measured under the specified experimental conditions in canine right ventricular muscle preparation. Data are expressed as mean ± SEM, n = number of measurements/number of animals.</p

Lack of effect of diclofenac on the transient outward potassium (I_to) and on the inward rectifier potassium (I_K1) currents in canine ventricular myocytes.

<p>A, <i>top</i>: Representative I_to current traces under control conditions and after application of 50 µM diclofenac. A, <i>bottom</i>: Current – voltage relationships of I_to under control conditions and in the presence of 50 µM diclofenac. Panel B shows steady-state current – voltage relationships of I_K1 before and after application of 50 µM diclofenac. Insets depict the voltage protocol applied during measurements. Data are expressed as mean ± SEM, n = number of measurements/number of animals.</p

Effect of diclofenac on action potentials in canine right ventricular muscle preparations and in Purkinje fibers.

<p>Representative superimposed records (<i>top</i>) demonstrating the effect of 20 µM diclofenac on action potential configuration at 1 s stimulation cycle length (<b>A</b>, right ventricular muscle; <b>B</b>, Purkinje fiber). Cycle length dependent changes in action potential duration (APD₉₀) measured under control conditions and in the presence of 20 µM diclofenac (<i>bottom</i>) in canine right ventricular muscle preparations (<b>A</b>) and in Purkinje fibers (<b>B</b>). Data are expressed as mean ± SEM, n = number of measurements/number of animals.</p

Effect of diclofenac on the rapid (I_Kr) and slow (I_Ks) component of the delayed rectifier potassium currents in canine ventricular myocytes.

<p><i>Top</i> panels show representative current traces (A, I_Kr; B, I_Ks), <i>bottom</i> panels represent current – voltage relationships under control conditions and in the presence of 30 µM diclofenac. Insets indicate the voltage protocol applied during measurements. Data are expressed as mean ± SEM, n = number of measurements/number of animals.</p