Fokozott aritmiaérzékenységgel társuló kamrai szívizom-remodelling vizsgálata sportszív nagyállatmodellben

A közelmúltban több tanulmány is rámutatott arra, hogy az intenzív sporttevékenység szívritmuszavarok kialakulására hajlamosíthat és akár hirtelen szívhalálhoz is vezethet, azonban a háttérben húzódó elektrofiziológiai mechanizmusok kevéssé ismertek. Munkánk során a tartós állóképességi edzés indukálta szívizom-átépülést (ún. „remodelling”) és aritmiaérzékenységet vizsgáltuk kutya sportszív-modellben. Beagle-kutyákat véletlenszerűen „kontroll” és „edzett” csoportokba soroltunk (n=12/csoport), ez utóbbi egy 4 hónapos intenzív edzésprogramban vett részt. A szívizom-remodellációt és a ritmuszavar-érzékenységet számos in vivo és in vitro technikával vizsgáltuk (elektrokardiográfia, echokardiográfia, közvetlen kamrai „burst” ingerlés, patch-clamp, immunocitokémia, szövettani vizsgálatok). Az edzésprogram hatására nőtt a szeptális falvastagság (8,1±0,2 mm vs. 7,4±0,2 mm; p<0,05), a bal kamrai végdisztolés átmérő (32,0±0,7 mm vs. 30,4±0,7 mm; p<0,05) és a bal kamrai tömegindex (125,8±4,3 g/m2 vs. 97,7±6,4 g/m2 ; p<0,05). Megnyúlt kamrai repolarizációt figyeltünk meg in vivo és in vitro körülmények között (QTc: 237,1±3,4 ms vs. 213,6±2,8 ms; APD90: 472,8±29,6 ms vs. 370,1±32,7 ms; p<0,05), amelyek a repolarizáció emelkedett rövid távú variabilitásával társultak. Az edzett állatok szívéből izolált bal kamrai szívizomsejtek tranziens kifelé irányuló K+-áramának amplitúdója csökkent (6,4±0,5 pA/pF vs. 8,8±0,9 pA/ pF, 50 mV; p<0,05), mindemellett a bal kamrai fibrózis mértéke, illetve a HCN4-fehérje expressziója is emelkedett. Fokozott ektópiás aktivitást és aritmiaérzékenységet figyeltünk meg az edzett állatokban. Modellünkben egyértelmű strukturális és elektrofiziológiai szívizom-átalakulás jelentkezett. Szívmorfológiai megfigyeléseink összhangban állnak a humán állóképességi élsportolókban megfigyeltekkel. Tanulmányunkban a repolarizáció diszperziójának fokozódása, a fibrózis emelkedett mértéke és a HCN4-túlexpresszió a modell aritmiák iránti fokozott érzékenységét jelzik

Selective Inhibition of Cardiac Late Na+ Current Is Based on Fast Offset Kinetics of the Inhibitor

The present study was designed to test the hypothesis that the selectivity of blocking the late Na+ current (INaL) over the peak Na+ current (INaP) is related to the fast offset kinetics of the Na+ channel inhibitor. Therefore, the effects of 1 µM GS967 (INaL inhibitor), 20 µM mexiletine (I/B antiarrhythmic) and 10 µM quinidine (I/A antiarrhythmic) on INaL and INaP were compared in canine ventricular myocardium. INaP was estimated as the maximum velocity of action potential upstroke (V+max). Equal amounts of INaL were dissected by the applied drug concentrations under APVC conditions. The inhibition of INaL by mexiletine and quinidine was comparable under a conventional voltage clamp, while both were smaller than the inhibitory effect of GS967. Under steady-state conditions, the V+max block at the physiological cycle length of 700 ms was 2.3% for GS967, 11.4% for mexiletine and 26.2% for quinidine. The respective offset time constants were 110 ± 6 ms, 456 ± 284 ms and 7.2 ± 0.9 s. These results reveal an inverse relationship between the offset time constant and the selectivity of INaL over INaP inhibition without any influence of the onset rate constant. It is concluded that the selective inhibition of INaL over INaP is related to the fast offset kinetics of the Na+ channel inhibitor

Cardiac electrophysiological effects of ibuprofen in dog and rabbit ventricular preparations: Possible implication to enhanced proarrhythmic risk

Ibuprofen is a widely used nonsteroidal anti-inflammatory drug, which has recently been associated with increased cardiovascular risk, but its electrophysiological effects have not yet been properly studied in isolated cardiac preparations. We studied the effects of ibuprofen on action potential characteristics and several transmembrane ionic currents using the conventional microelectrode technique and the whole-cell configuration of the patch-clamp technique on cardiac preparations and enzymatically isolated ventricular myocytes. In dog (200 µM; n = 6) and rabbit (100 µM; n = 7) papillary muscles, ibuprofen moderately but significantly prolonged repolarization at 1 Hz stimulation frequency. In dog Purkinje fibers, repolarization was abbreviated and maximal rate of depolarization was depressed in a frequency-dependent manner. Levofloxacin (40 µM) alone did not alter repolarization, but augmented the ibuprofen-evoked repolarization lengthening in rabbit preparations (n = 7). In dog myocytes, ibuprofen (250 µM) did not significantly influence IK1, but decreased the amplitude of Ito and IKr potassium currents by 28.2% (60 mV) and 15.2% (20 mV), respectively. Ibuprofen also depressed INaL and ICa currents by 19.9% and 16.4%, respectively. We conclude that ibuprofen seems to be free from effects on action potential parameters at lower concentrations. However, at higher concentrations it may alter repolarization reserve, contributing to the observed proarrhythmic risk in patients.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Synthesis and Conformational Analysis of Naphthoxazine-Fused Phenanthrene Derivatives

The synthesis of new phenanthr[9,10-e][1,3]oxazines was achieved by the direct coupling of 9-phenanthrol with cyclic imines in the modified aza-Friedel&ndash;Crafts reaction followed by the ring closure of the resulting bifunctional aminophenanthrols with formaldehyde. Aminophenanthrol-type Mannich bases were synthesised and transformed to phenanthr[9,10-e][1,3]oxazines via [4 + 2] cycloaddition. Detailed NMR structural analyses of the new polyheterocycles as well as conformational studies including Density Functional Theory (DFT) modelling were performed. The relative stability of ortho-quinone methides (o-QMs) was calculated, the geometries obtained were compared with the experimentally determined NMR structures, and thereby, the regioselectivity of the reactions has been assigned

Late Na+ Current Is [Ca2+]i-Dependent in Canine Ventricular Myocytes

Enhancement of the late sodium current (INaL) increases arrhythmia propensity in the heart, whereas suppression of the current is antiarrhythmic. In the present study, we investigated INaL in canine ventricular cardiomyocytes under action potential voltage-clamp conditions using the selective Na+ channel inhibitors GS967 and tetrodotoxin. Both 1 µM GS967 and 10 µM tetrodotoxin dissected largely similar inward currents. The amplitude and integral of the GS967-sensitive current was significantly smaller after the reduction of intracellular Ca2+ concentration ([Ca2+]i) either by superfusion of the cells with 1 µM nisoldipine or by intracellular application of 10 mM BAPTA. Inhibiting calcium/calmodulin-dependent protein kinase II (CaMKII) by KN-93 or the autocamtide-2-related inhibitor peptide similarly reduced the amplitude and integral of INaL. Action potential duration was shortened in a reverse rate-dependent manner and the plateau potential was depressed by GS967. This GS967-induced depression of plateau was reduced by pretreatment of the cells with BAPTA-AM. We conclude that (1) INaL depends on the magnitude of [Ca2+]i in canine ventricular cells, (2) this [Ca2+]i-dependence of INaL is mediated by the Ca2+-dependent activation of CaMKII, and (3) INaL is augmented by the baseline CaMKII activity

Late Na+ Current Is [Ca2+]i-Dependent in Canine Ventricular Myocytes

Enhancement of the late sodium current (INaL) increases arrhythmia propensity in the heart, whereas suppression of the current is antiarrhythmic. In the present study, we investigated INaL in canine ventricular cardiomyocytes under action potential voltage-clamp conditions using the selective Na+ channel inhibitors GS967 and tetrodotoxin. Both 1 µM GS967 and 10 µM tetrodotoxin dissected largely similar inward currents. The amplitude and integral of the GS967-sensitive current was significantly smaller after the reduction of intracellular Ca2+ concentration ([Ca2+]i) either by superfusion of the cells with 1 µM nisoldipine or by intracellular application of 10 mM BAPTA. Inhibiting calcium/calmodulin-dependent protein kinase II (CaMKII) by KN-93 or the autocamtide-2-related inhibitor peptide similarly reduced the amplitude and integral of INaL. Action potential duration was shortened in a reverse rate-dependent manner and the plateau potential was depressed by GS967. This GS967-induced depression of plateau was reduced by pretreatment of the cells with BAPTA-AM. We conclude that (1) INaL depends on the magnitude of [Ca2+]i in canine ventricular cells, (2) this [Ca2+]i-dependence of INaL is mediated by the Ca2+-dependent activation of CaMKII, and (3) INaL is augmented by the baseline CaMKII activity