Tiny gates in cell membranes that control which charged particles (calcium, sodium, potassium) enter or leave the cell. Ion channels are protein structures embedded in the membrane that form selective pores for ions to pass through. Because PEMF induces a small electric field in tissue, it may influence how these gates open and close, which is one of the proposed pathways for how PEMF interacts with cells. What that means for any particular response depends on the field and the tissue together.
A living cell holds a small voltage across its membrane, more positive on one side than the other. Channels in the membrane let charged ions cross, which shifts that voltage. This is the electrical side of a cell that a changing magnetic field can interact with. It is background biology, not a claim about any specific outcome.
