Figure 1. Isradipine renders Optopatch-Spiking HEK cells susceptible to arrhythmia.
A) Molecular components of the synthetic excitable tissue. The voltage-gated sodium channel NaV1.5 and inward-rectifying potassium channel Kir2.1 are together sufficient to produce action potentials in response to a depolarizing stimulus. CheRiff is a blue-shifted channelrhodopsin which depolarizes the cells in response to blue light, and BeRST1 is a dye which reports voltage through changes in red fluorescence. Connexin channels (Cxn) introduce electrical coupling between neighboring cells. B) Left: microcontact printing defines patterns of cell growth. The vertical stripes connect in a serpentine pattern outside the field of view. Blue overlay shows regions of optogenetic stimulation. Zero-dimensional “islands” are tested alongside one-dimensional “tracks”. Right: single frame from a movie of BeRST1 fluorescence showing traveling waves in the track region. See Supplementary Movie 1. Scale bars 500 mm. C) Fluorescence recordings of membrane voltage showing that isradipine (10 μM) induces alternans in OS-HEK cells paced at 4 Hz. D) At low pace frequency isradipine OS-HEK (iOS-HEK) cells beat periodically in synchrony with the pacing, but at high pace frequency the cells produce an irregular rhythm.