Previous studies of reentrant arrhythmias in the heart have been performed in computer models and tissue experiments. We hypothesized that confluent monolayers of cardiac cells can provide a simple, controlled, and reproducible experimental model of reentry. Neonatal rat ventricular cells were cultured on 22-mm-diameter coverslips and stained with the voltage-sensitive dye RH-237. Recordings of transmembrane potentials were obtained from 61 sites with the use of a contact fluorescence imaging system. An electrical field stimulus, followed by a point stimulus, induced 39 episodes of sustained reentry and 21 episodes of nonsustained reentry. Sustained reentry consisted of single-loop (n ϭ 18 monolayers) or figure-of-eight (n ϭ 4) patterns. The cycle length, action potential duration at 80% repolarization, and conduction velocity were (in means Ϯ SE) 358 Ϯ 33 ms, 118 Ϯ 12 ms, and 12.9 Ϯ 1.0 cm/s for single loop and 311 Ϯ 78 ms, 137 Ϯ 18 ms, and 7.8 Ϯ 1.3 cm/s for figure-of-eight, respectively. Electrical termination by 6-to 13-V/cm field pulses or 15-to 20-V point stimuli was successful in 60% of the attempts. In summary, highly stable reentry can be induced, sustained for extensive periods of time, and electrically terminated in monolayers of cultured neonatal rat cardiac myocytes. arrhythmia; cardiac electrophysiology; voltage-sensitive dye; optical mapping UNIDIRECTIONAL CONDUCTION block and formation of wave breaks during propagation in heart muscle can result in self-sustained propagation of electrical and mechanical activity, in which an activation wave front can reenter the same area after propagating around a fixed anatomic or functional obstacle (9). Functional reentry is generally accepted to be the major mechanism underlying many monomorphic and polymorphic tachycardias, which can evolve into irregular electrical activity such as atrial or ventricular flutter and fibrillation. Although the initiation and cardioversion of functional reentry have been subjects of numerous theoretical and experimental studies (2-4, 12, 23, 24, 27, 31, 33), there still exists a need for the development of new model systems that can aid in the understanding and treatment of these life-threatening arrhythmias.The use of cultured monolayers of cardiac cells as a simplified model for the study of functional cardiac electrophysiology offers many advantages, including: 1) control of the cell microenvironment, 2) elimination of excitation-contraction decouplers that are used for optical mapping but may alter the electrophysiological properties of the cells (17, 18), 3) removal of large scale tissue heterogeneities such as blood vessels, connective tissue, or rotational anisotropy, and 4) the certainty that the electrophysiological signals are produced from a known layer of cells, thus enabling a one-to-one correspondence with two-dimensional computer simulations and nonlinear dynamic theory. Currently, there is a gap between the computer simulations, which assume an ideal homogeneous excitable media, and tissue experiments, where ...

Kong, Chae-Ryon, Nenad Bursac, and Leslie Tung. Mechanoelectrical excitation by fluid jets in monolayers of cultured cardiac myocytes. J Appl Physiol 98: 2328 -2336, 2005. First published February 24, 2005 doi:10.1152/japplphysiol.01084.2004.-Although the prevailing view of mechanoelectric feedback (MEF) in the heart is in terms of longitudinal cell stretch, other mechanical forces are considerable during the cardiac cycle, including intramyocardial pressure and shear stress. Their contribution to MEF is largely unknown. In this study, mechanical stimuli in the form of localized fluid jet pulses were applied to neonatal rat ventricular cells cultured as confluent monolayers. Such pulses result in pressure and shear stresses (but not longitudinal stretch) in the monolayer at the point of impingement. The goal was to determine whether these mechanical stimuli can trigger excitation, initiate a propagated wave, and induce reentry. Cells were stained with the voltage-sensitive dye RH237, and multi-site optical mapping was used to record the spread of electrical activity in isotropic and anisotropic monolayers. Pulses (10 ms) with velocities ranging from 0.3 to 1.8 m/s were applied from a 0.4-mm diameter nozzle located 1 mm above the cell monolayer. Fluid jet pulses resulted in circular wavefronts that propagated radially from the stimulus site. The likelihood for mechanical stimulation was quantified as an average stimulus success rate (ASSR). ASSR increased with jet amplitude and time waited between stimuli and decreased with the application of gadolinium and streptomycin, blockers of stretch-activated channels, but not with nifedipine, a blocker of the L-type Ca channel. Absence of cellular injury was confirmed by smooth propagation maps and propidium iodide stains. In rare instances, the mechanical pulse resulted in the induction of reentrant activity. We conclude that mechanical stimuli other than stretch can evoke action potentials, propagated activity, and reentrant arrhythmia in two-dimensional sheets of cardiac cells. mechanoelectrical coupling; ventricular arrhythmias; optical mapping; cell culture; neonatal rat NUMEROUS STUDIES have shown that mechanical stretch or load applied to a cardiac tissue can induce significant electrophysiological effects via the process termed "mechanoelectric feedback" (MEF). Mechanically triggered action potentials have been observed with sudden stretch of the ventricles (20), stretch of the isolated ventricular free wall (17), or mechanical stimulation of single cardiac myocytes (13,28,42). Mechanical stretch also changes action potential duration (42, 48, 51), excitability (45), and expression of gap junctional channels (52). The electrophysiological effects have been attributed mainly to the activity of stretch-activated ion channels (SACs) (26). Pharmacological agents that inhibit SAC activity include streptomycin (21), gadolinium (Gd 3ϩ ) (26), and the tarantula toxin .The mechanically induced premature ventricular beats mentioned above can be proarrhythmic. As a dramati...