Anisotropic conduction block and reentry in neonatal rat ventricular myocyte monolayers

Abstract

conduction block and reentry in neonatal rat ventricular myocyte monolayers. Am J Physiol Heart Circ Physiol 300: H271-H278, 2011. First published October 29, 2010 doi:10.1152/ajpheart.00758.2009.-Anisotropy can lead to unidirectional conduction block that initiates reentry. We analyzed the mechanisms in patterned anisotropic neonatal rat ventricular myocyte monolayers. Voltage and intracellular Ca (Ca i) were optically mapped under the following conditions: extrastimulus (S1S2) testing and/or tetrodotoxin (TTX) to suppress Na current availability; heptanol to reduce gap junction conductance; and incremental rapid pacing. In anisotropic monolayers paced at 2 Hz, conduction velocity (CV) was faster longitudinally than transversely, with an anisotropy ratio [AR ϭ CV L/CVT, where CVL and CVT are CV in the longitudinal and transverse directions, respectively], averaging 2.1 Ϯ 0.8. Interventions decreasing Na current availability, such as S1S2 pacing and TTX, slowed CV L and CVT proportionately, without changing the AR. Conduction block preferentially occurred longitudinal to fiber direction, commonly initiating reentry. Interventions that decreased gap junction conductance, such as heptanol, decreased CV T more than CVL, increasing the AR and causing preferential transverse conduction block and reentry. Rapid pacing resembled the latter, increasing the AR and promoting transverse conduction block and reentry, which was prevented by the Ca i chelator 1,2-bis oaminophenoxy ethane-N,N,N=,N=-tetraacetic acid (BAPTA). In contrast to isotropic and uniformly anisotropic monolayers, in which reentrant rotors drifted and self-terminated, bidirectional anisotropy (i.e., an abrupt change in fiber direction exceeding 45°) caused reentry to anchor near the zone of fiber direction change in 77% of monolayers. In anisotropic monolayers, unidirectional conduction block initiating reentry can occur longitudinal or transverse to fiber direction, depending on whether the experimental intervention reduces Na current availability or decreases gap junction conductance, agreeing with theoretical predictions.anisotropy; reentry; myocyte monolayers; optical mapping CARDIAC TISSUE IS INHERENTLY anisotropic, with faster conduction velocity (CV) along fiber direction than across it (24, 29, 31), a property implicated in arrhythmogenesis. Spach et al. (31) showed that anisotropy can lead to preferential longitudinal conduction block initiating reentry, due to a lower safety factor for longitudinal than transverse conduction. Other investigators, however, found preferential transverse conduction block in anisotropic tissue (7,8,22,24,26), particularly when gap junction conductance was pharmacologically decreased by heptanol (8). Although theoretical mechanisms for both preferential longitudinal block (due to reduced safety factor) (27, 31) and preferential transverse block [due to reduced gap junction conductance (13) and certain low excitability conditions (8)] have been proposed, the experimental evidence for these mechanisms in intact thre...

The voltage-sensitive dye di-4-ANEPPS slows conduction velocity in isolated guinea pig hearts

“…13,14 Changes in gap junctional coupling affect transverse conduction preferentially, causing a change in the anisotropy of propagation. 15,16 We did not observe any change in the anisotropy of propagation after staining with di-4-ANEPPS although the P value ( P = .056, compared with a critical significance level of d = 0.017) related to the comparison could be considered trending toward increased anisotropy. As di-4-ANEPPS slowed conduction less than carbenoxolone, where, as expected, a change in anisotropy was detected, it is possible that the degree of conduction slowing with di-4-ANEPPS was too small to detect a potential change in anisotropy.…”

Surface Chemistry and Microtopography of Parylene C Films Control the Morphology and Microtubule Density of Cardiac Myocytes

“…[5][6][7][8][9] Several different methodologies have been developed for cardiac tissue engineering using neonatal rat ventricular myocytes (NRVM) 2,[5][6][7][8][9] and induced pluripotent stem cellderived cardiomyocytes. 1 These techniques include microcontact printing of substrates with extracellular matrix (ECM) compounds, 5 deposition of ECM proteins and cells through microfluidic channels, 10 microgrooved substrates, 1,5,6,8,9 nanotextured hydrogels, 11 and lithographically patterned substrates. 2,7 Structured cardiomyocyte cultures have also been realized in three dimensions with the use of naturally or synthetically produced ECMs produced through electrospinning of aligned polymer nanofibers 12 and production of macroporous preformed scaffolds with complex biomimetic pore structures.…”

Multicellular In vitro Models of Cardiac Arrhythmias: Focus on Atrial Fibrillation

“…(44,(55)(56)(57)(58)(59)(60)(61) Currently, NVRMs are the most widely used model to study cardiac arrhythmias as evidenced by the large number of research papers, in which these cells are used (62)(63)(64)(65). This is exemplified by studies with NRVMs that looked at the effects of ischemia/reperfusion injury, anisotropy, fibrosis, CM-(myo)fibroblasts coupling, hypertrophy as well as changes in the activity of ion channels and gap junctions on cardiac arrhythmias (66)(67)(68)(69)(70)(71)(72)(73)(74)(75)(76)(77)(78). Although arrhythmia mechanisms uncovered by investigation of ventricular CMs may also be relevant for understanding the initiation and maintenance of atrial arrhythmias, there are marked differences between ventricular and atrial CMs on a structural and electrophysiological level (79-82), making it crucial to use atrial CMs for the modeling atrial arrhythmias like AF.…”