Abstract 1349: Overexpression And Dominant-negative Suppression Of Inwardly Rectifying Potassium Channel Protein (Kir2.1) Alters Electrophysiology And Spiral Wave Dynamics Of An In Vitro Model Of Cardiac Myocytes
Introduction: An important role for the inwardly rectifying potassium current (IK1) has been postulated in controlling the stability and frequency of rotors responsible for ventricular tachycardia and fibrillation. We investigated the effects of Kir2.1 overexpression and Kir2.1AAA dominant-negative mutant suppression on the electrophysiology and inducibility, stability and frequency of spiral waves in an in vitro cardiac tissue model.
Methods/Results: Neonatal rat ventricular myocytes (NRVMs) were transduced by lentiviral vectors encoding Kir2.1 or Kir2.1AAA. Immunostaining revealed Kir2.1 or mutant Kir2.1 protein overexpression and whole cell-clamp confirmed the predicted effects on IK1, resting potential, and action potential duration (APD80). Optical mapping was performed on confluent NRVM monolayers containing a 5 mm diameter central island of gene-modified NRVMs created by a stenciling technique. APs propagated with increased CV (25.1±2.7 cm/sec, n=7) and shortened APD80 (73±11 msec, n=7) in islands of Kir2.1 overexpression, or decreased CV (13.1±1.1 cm/sec, n=7) and prolonged APD80 (263±14 msec, n=7) in islands of Kir2.1AAA suppression, compared with normal CV and APD80 of 19.2±0.4 cm/sec and 169±14 msec (n=7) in non-transduced islands. Reentry was initiated by rapid pacing. With Kir2.1 overexpression, reentrant waves anchored to the island and remained stable (89±15 minutes, n=3) with a frequency of 8±2 Hz. Superfusion with 0.5 mM BaCl2 to block IK1 slowed reentry to 1 Hz and terminated it shortly after initiation. NRVM monolayers with islands of Kir2.1AAA suppression (n=3) displayed rapid spontaneous activity. Rapid pacing of these monolayers initiated an unstable figure-of-eight reentry (n=3) that degraded into single and multi-armed spiral waves, anchored to varying parts of the island with a maximum frequency of 2±1 Hz. Importantly, no reentry could be initiated in monolayers with non-transduced islands (n=3).
Conclusion: Functional reentrant waves induced by rapid pacing are anchored to islands of localized Kir2.1 overexpression whereas they drop in frequency and meander in islands of dominant-negative suppression of Kir2.1, confirming the importance of IK1 for the stability of these waves in cardiac tissue.