1. the same ions moving through different channels can have different consequences. Consider the example of potassium ions. When it moves through a:
- nongated channel, it establishes the resting potential
- a voltage gated channel, it repolarizes the cell after an action potential
- channel that is gated by chemical modification (such as phosphorylation), it may hyperpolarize the membrane (make it more negative inside) and facilitate neuron inhibition
2. If two ions are involved in signaling, the result depends on
- if the two species move simultaneously through the same channel (which results in excitation through an initial depolarization of membrane if the ions are potassium and sodium)
- if the two species move through different channels in a sequential fashion (which generates an action potential) if the ions are potassium and sodium).
In summary, ligand and voltage gated channels allow changes in the polarization of the membrane. Other mechanisms can also lead to changes. Membrane proteins can be phosphorylated (using ATP) by protein kinases in the cell, leading to a change in the conformation of the membrane protein, and either an opening or closing of the channel. Channels linked to the cytoskeleton of the cells can also be opened or closed through stretching. Other stimuli that gate channels are light (through photoisomerization-induced conformational changes), heat, and cold.