Abstract 10169: Roles of Action Potential Duration Gradient in Remote Conduction Block: in vitro Studies of Micropatterned Heterocellular Strands
Spatial gradients in cell coupling, conduction velocity (CV), and action potential duration (APD) are known to occur in normal and diseased hearts and potentially at a host-donor interface following cell-based cardiac therapies. Depending on their intensity and spatial extent, these gradients in electrical properties can facilitate the occurrence of unidirectional conduction block and reentry. In this study, we optically mapped 150 ∝m-wide micropatterned cell strands containing a distinct, continuous interface between genetically-engineered excitable HEK-293 cells (“Ex293s”, stably expressing Nav1.5, Kir2.1, and connexin-43 channels) and neonatal rat ventricular myocytes (NRVMs) (Fig A). Point stimulation from the Ex293 end of the strand yielded the formation of a large APD gradient (267.1±22.9 ms/mm) between Ex293s (APD = 30.7±0.6 ms) and NRVMs (APD = 135.7±9.4 ms) despite uniform impulse conduction (Fig B). Application of a premature stimulus after steady pacing at 2 Hz resulted in a conduction block at the Ex293-NRVM interface when S1S2 coupling interval was reduced below 118.2±3.6% of the cardiomyocyte APD measured at 2 Hz. An increase in the pacing rate from 2 Hz to 4 and 6 Hz resulted in a selective restitution-based APD shortening in the NRVM region, yielding corresponding reductions in the maximum APD gradient of -11.9% and -20.9% (Fig. C). Partial block of the inward rectifier potassium current (IK1) by 50 ∝M BaCl2 during 2 Hz pacing caused a more pronounced APD prolongation in Ex293 than NRVM region, thus reducing the maximum APD gradient by -45.3±8.1% (Fig. D). Application of the gap junctional blocker carbenoxolone yielded a +27.4±3.5% increase in the APD gradient without a change in either NRVM or Ex293 APDs. The described heterocellular strand setting provides a unique in vitro platform to systematically examine the roles of APD and CV gradients in vulnerability to unidirectional conduction block.
- © 2011 by American Heart Association, Inc.