Question

If a ligand-gated channel (ionotropic receptor) was activated by a negatively charged ion with a negative equilibrium potential, would it result in an Excitatory post synaptic potential or an inhibitory post synaptic potential?

Answer 1

If a ligand-gated channel (ionotropic receptor) was activated by a negatively charged ion with a negative equilibrium potential,it would result in an Inhibitory post synaptic potential.

Ligand-gated ion channels are a group of intrinsic transmembrane proteins that when activated by a specific chemical(Neurotransmitter/Hormone/Specific ions) allow passage of ions .

Ligands can bind extracellularly-For example 1. glutamate 2.ACh 3. GABA

Or they Bind Intracellularly-For example-Ca2+ or calcium activated K+ (Here also, ligand itself is not transported across the membrane,But Ligand binding causes a increase in the permeability of the channel to a specific ion)

The ionotropic Receptors are either Cation Selective or Anion Selective-

*Cation selective Ionotropic receptors are Excitatory whereas Anion selective ionotropic receptors are Inhibitory to Neurotrasmission.

Example for cation selective ionotropic receptors-NMDA, 5-HT3,AMPA, nicotinic receptors..

Example for anion selective ionotropic receptors-, glycine,GABA-A.

Both these anion selective ionotropic receptors-(Glycine,GABA-A) conduct negative current by the influx of chloride ions and hyperpolarization of membranes, thereby inhibit presynaptic membrane neurotransmission .