Acute Sodium Flux as a Driver of Morphological and Motility Instability in MDA-MB-231 and MCF-7 Breast Cancer Cells

Voltage-gated sodium channels (VGSCs) are increasingly recognised as regulators of cancer cell behaviour. In triple negative breast cancer (TNBC), a subtype of breast cancer that lacks oestrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) expression, the neonatal splice variant of Nav1.5 generates a persistent inward sodium current that drives membrane depolarisation, Na⁺/H⁺ exchange and cytoskeletal remodelling. Although VGSC inhibition is known to suppress invasion, the immediate cellular consequences of sustaining Nav1.5 activity remain unclear. This study examined how altering VGSC function, either by blocking the channel or sustaining its activity, affects viability, morphology and motility across short but mechanistically informative time scales in Nav1.5-positive MDA-MB-231 cells and Nav1.5-deficient MCF-7 cells.
The VGSC inhibitor ranolazine in MDA-MB-231 cells produced minimal effects over the short-term windows tested (5 min to 24 h), consistent with low basal persistent sodium current under normoxia. In contrast, sustaining VGSC activity with aconitine triggered rapid ionic and mechanical instability detectable within min, including acute reductions in cell area, increased displacement features and early loss of cell number. High-temporal-resolution brightfield imaging (20 second intervals) revealed rapid morphological contraction that was not detectable by longer-interval imaging platforms. Although these early disturbances impaired wound closure at an early and later stages, aconitine did not activate caspase-3/7, suggesting a caspase-independent mechanism possibly driven by sodium loading and osmotic imbalance. Short-term phenotypic changes inMCF-7 cells lacking functional Nav1.5, aconitine reduced viability in a dose-dependent manner following 2 hours of treatment and induced subtle but reproducible morphology alterations, with increased motility/displacement parameters discriminating treated cells from controls, consistent with cytoskeletal disruption. Overall, this work demonstrates that the timing of VGSC modulation is critical: sustaining channel activity produces immediate and pronounced phenotypic changes, whereas blocking Nav1.5 yields limited smaller effects under a normoxic environment. These findings support a model in which sodium flux integrates physiological changes on rapid timescales to shape the invasive phenotype of breast cancer cells.