**2.1. Resting potential and calcium oscillations in breast cancer**

The resting potential of human breast adenocarcinoma cells (estrogen receptor-positive MCF7 and triple-negative MDA-MB-231) is more positive (with approximately 27–30 mV) than normal

**Figure 2.** Proteins associated with calcium signaling pathways that have been described to undergo alterations in breast cancer cells.

human mammary epithelial cells [76]. Additionally, breast cancer cells react distinctly with respect to normal mammary epithelial cells in response to the changes in the extracellular ions (e.g., K<sup>+</sup> or Ca2+) [76]. The differences in resting potential between breast cancer cells and normal cells may be useful in the development of anticancer-targeted therapies based on charged liposomes, which are considered among the promising liposome-based therapeutical approaches [77].

MDA-MB-231 breast cancer cells with high-metastatic potential also exhibit spontaneous Ca2+ oscillations in comparison with MCF7 breast cancer cells with a low-metastatic potential [78]. Interestingly, these spontaneous oscillations were absent in breast cancer cells with a low-metastatic potential, even in increased extracellular K<sup>+</sup> concentration conditions that determined the augmentation of their basal Ca2+ level [78]. This feature of presenting spontaneous calcium oscillations in metastatic cells might be further exploited in understanding the cellular mechanisms standing behind and in finding adequate therapies.
