Opioid Actions on Membrane Ion Channels

Abstract

Drugs, hormones, and neurotransmitters can open and close ion channels by several molecular mechanisms. First, the transmitter receptor might itself comprise the ion channel: examples are the nicotinic acetylcholine (ACh) receptors, the glutamate receptors, γ-aminobutyric acid (GABAA) receptors, 5-hydroxytryptamine (5-HT3) receptors, and adenosine 5’- triphosphate (ATP P2x) receptors (North 1989a). In this case, the channel is named for the transmitter that causes it to open whereas other channels are usually named for the ions that pass through them. The movement of ions through such ligand-gated channels has immediate electrical consequences and may have secondary metabolic consequences; for example, significant entry of calcium ions through the channel may activate intracellular enzymes.