Ligand gated ion channels (LGICs) are a type of ionotropic receptor of channel-linked receptor. They are a group of transmembrane ion channels that are opened and closed in direct response to the binding of a chemical messenger, a ligand, such as a neurotransmitter. The link between the ligand and the opening and closing of the ion channel is direct, and is contrasted with the indirect function of the metabutropic receptor, which uses second messengers. Second messengers are molecules that relay signals from receptors on the cell's surface to target molecules inside the cell, in the cytoplasm or in the nucleus. Second messenger molecules affect something else, which in turn, affects something else located within the cell.
G-protein gated ion channels are specific ion channels located in the plasma that are directly activated by a family of associated proteins. They are specifically responsible for maintaining the elctrochemical gradient across the cell.