Ionomycin is a calcium ionophore used to increase intracellular calcium concentration, it does so by:

1. Facilitating the transport of Ca²⁺ across the plasma membrane.
2. Releasing Ca²⁺ from its intracellular stores without the involvement of G proteins, resulting in the activation of calcium-activated chlorine channels.
3. Acts on the same intracellular Ca²⁺ stores as 'P3