Voltage imaging reveals the dynamic electrical signatures of human breast cancer cells.

Cancer cells feature a resting membrane potential (V m ) that is depolarized compared to normal cells, and express active ionic conductances, which factor directly in their pathophysiological behavior. Despite similarities to 'excitable' tissues, relatively little is known about cancer cell V m dynamics. Here high-throughput, cellular-resolution V m imaging reveals that V m fluctuates dynamically in several breast cancer cell lines compared to non-cancerous MCF-10A cells. We characterize V m fluctuations of hundreds of human triple-negative breast cancer MDA-MB-231 cells. By quantifying their Dynamic Electrical Signatures (DESs) through an unsupervised machine-learning protocol, we identify four classes ranging from "noisy" to "blinking/waving". The V m of MDA-MB-231 cells exhibits spontaneous, transient hyperpolarizations inhibited by the voltage-gated sodium channel blocker tetrodotoxin, and by calcium-activated potassium channel inhibitors apamin and iberiotoxin. The V m of MCF-10A cells is comparatively static, but fluctuations increase following treatment with transforming growth factor-β1, a canonical inducer of the epithelial-to-mesenchymal transition. These data suggest that the ability to generate V m fluctuations may be a property of hybrid epithelial-mesenchymal cells or those originated from luminal progenitors.