Which of the following statements is not true about a ligand-gated ion channel receptor?

a) Ligand-gated ion channel receptors are present in the cell membrane.

b) Neurotransmitters can act as the chemical messengers for ligand-gated ion channels.

c) Ligand-gated ion channels consist of five glycoproteins.

d) Differences in membrane potential affect whether ligand-gated ion channel receptors open or close