Modulation of gated ion channels as a mode of transmitter action

Ionic channels in nerve and muscle cells have until recently been divided into two broad classes: channels that participate in the generation of the action potential and channels that generate postsynaptic potentials in response to neurotransmitters. This distinction was based to a large extent on the classic analysis of the action of acetylcholine (ACh) at the frog neuromuscular junction³¹ - where the cholinergic end-plate channels are different from the Hodgkin-Huxley Na⁺ and K⁺ channels that generate the action potential⁶². However, recent results suggest that in many other systems neurotransmitters can modulate the activity of channels that contribute to the action potential. This type of postsynaptic effect is responsible for several important physiological actions of transmitters⁴³. Patch-clamp experiments provide insights into the mechanisms of modulation at the level of single-channel molecules.