As more and more studies utilize cell-penetrating peptides to deliver pharmacologically interesting substances, there is a growing need to understand their effect on the plasma membrane. If a cell-penetrating peptide together with its cargo is to be used as a drug, it is necessary to understand how the conjugate interacts with the plasma membrane to enter the cell. A key regulator of the transportation network in the cell is calcium. This chapter describes five methods that can be employed for understanding how the plasma membrane reacts to the presence of cell-penetrating peptides and the involvement of calcium.
