Abstract 489: JTV-519 (K201) Reverses Abnormal Ca2+ Release And Dynamic Ca2+ Waves In Purkinje Cells From The Infarcted Canine Heart
JTV-519 (K201) has been shown to be anti-arrhythmic in the ischemic/reperfusion setting. The mechanism is unknown.
Purpose: To investigate the effects of JTV-519(K201) (Aetas Pharm Co.) in Purkinje cells dispersed from the subendocardium of the 48hr infarcted canine heart (IZPCs). IZPCs are the source of the triggered ventricular arrhythmias that occur at this time post coronary artery occlusion.
Methods: Ca2+ release events (elevations of basal [Ca2+] equivalent to F/F0 3.4 SD over F0) in both intact and permeabilized single IZPCs were imaged using 2DCM with Fluo-4 and analyzed using a custom IDL program.
Results: In intact IZPCs, the Ca2+ release event (ev) rate was increased in the Subsarcolemmal region (SSL, a layer of ∼ 5μm thickness below the membrane; 0.0161±0.0031 ev/μm2/sec, n=cells=30, 1198 ev) but not in the Core region, when compared to normal Purkinje cells (NZPCs; SSL, 0.0089±0.0018 ev/μm2/sec, n=34, 747 ev, p<0.05). SR Ca2+ ontent as estimated by rapid caffeine (20mM) application was comparable between NZPCs and IZPCs in both subcellular regions. Superfusion of JTV-519(K201) (1μM) normalized the SSL Ca2+ event rate in intact IZPCs (to 0.0086±0.0016 ev/μm2/sec, n=17, 510ev, p<0.05 vs untreated IZPC value) without a change in SR Ca2+ content. The incidence of spontaneous Ca2+ waves is increased in intact IZPCs (0.0016/μm2/sec*1000, n=57) and was also normalized by JTV-519(K201)(0.0004/ μm2/sec*1000, n=30). In saponin-treated IZPCs ([Ca2+]cyto=100nM), JTV-519(K201) normalized the enhanced Ca2+ event rate (from 0.0246±0.0030 ev/μm2/sec, n=28 to 0.0110±0.0023 ev/μm2/sec, n=7, P<0.05).
Conclusion: In Purkinje cells that survive in the infarcted heart, the enhanced subcellular Ca2+ event rate is due to enhanced Ca2+ induced Ca2+ release. This leads to cell wide Ca2+ waves and arrhythmias. By normalizing Ca2+ sensitivity of Ca2+ release channels of IZPCs, JTV519(K201) reduces the spontaneous Ca2+ event rate, the incidence of Ca2+ waves and thus the likelihood of infarct Purkinje cell induced triggered arrhythmias.