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Rapid morphological changes induced by direct electrical stimulation of nerve terminals were studied by using video-enhanced differential interference contrast microscopy at a very high magnification (12,000x). We used mainly cultured bovine chromaffin cells, which developed neurite-like processes, and PC12 cells, which showed neuronal differentiation upon NGF treatment. In a few cases, primary neurons of the rat dorsal root ganglion were also examined. Brief pulse stimulation of the terminals and varicosities induced exocytosis accompanied by rapid formation of filopodia. These filopodia, 0.1–0.2 micron in diameter and up to 10 microns in length, formed within a few hundreds of milliseconds and then retracted within tens of seconds. They could also be induced by K depolarization. This rapid filopodial sprouting strongly depended on the presence of extracellular Ca2+ and could be abolished in a medium containing a Ca chelator (EGTA) or La2+. Anti-cytoskeletal agents colchicine and cytochalasin B failed to block this response completely but lidocaine fully suppressed it. Quantitative analysis of exocytosis and filopodial sprouting showed that they were independent events, not directly linked to each other, having different thresholds usually higher for filopodial formation. In PC12 cells, the extent of filopodial sprouting varied with the state of differentiation of the cells, suggesting a functional role of rapid sprouting during a particular phase of their differentiation. Filopodia could be induced with greater ease by repetitive stimulation. The same responses may occur at growth cones approaching the target cells or even at mature synapses particularly after repetitive electrical activity, possibly playing a role in use-dependent synapse formation or plasticity.

Digitoxin belongs to a naturally occurring class of cardiac glycosides (CG); digitoxin is clinically approved for heart failure and known for its anti-cancer effects against non-small lung cancer cells (NSCLC). However, concerns associated with its narrow therapeutic index and its concentration-dependent mechanism of action are rising. Thus, before digitoxin implementation in designing and developing safer and more effective CG-based anti-cancer therapies, its pharmacological and safety profiles need to be fully elucidated. In this research we used a combinatorial approach to evaluate the anti-cancer mechanisms of digitoxin in real-time. Our approach employed a non-invasive electric cell impedance sensing technique as a proxy to monitor NSCLC behavior post-exposure to toxic, therapeutic and sub-therapeutic concentrations of the drug. By developing structure–function combinatorial relations we showed that digitoxin targets cancer cells in a time and dose-dependant manner by activating pro-apoptotic and anti-proliferative signaling cascades that results in strengthening cellular adhesion and sequestration of key regulatory proliferation protein from the nucleus.

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