Question

during what type of ligand-receptor signaling are ion channels opened or closed

Answer 1

Normally Neurotransmitters ligand receptor signaling ion channel will open or closed when transmitting the Signal.

As we know ligand are chemical, hormones or proteins molecules which helps in transmission of information from one cell to another.It works as modulators or inhibitor which means it helps in the conformational changes in the receptor molecules which results into transfer of signals.... ( It is diiferent from voltage gated channel which open or close in response to membrane potential depends on voltage of ions whereas it only depends on chemical ( neurotransmitter) release/ response)

When ligand receptor are ions channels then it normally termed as ionotropic channel signaling ,in which CHEMICAL RESPONSE is necessary for signaling.There are normal barrier in transmembrane ionotropic Signaling called "GATE " ,which will be open only when get signal( conformational change occur in them ).

Neurotransmitter signalling are one of the important example of this type of signaling.As we know each presynaptic neurons release only one neurotransmitter and after releasing it only binds to the receptor present in the plasmamembrane of post synaptic neurons .The channel will open only when a neurotransmitter binds with correct receptor,which helps in their conformational changes results into opening of channel gate.When gate will open then either excitatory postsynaptic potential (EPSP) or inhibitiory postsynaptic potential (IPSP) reached. The IPSP is causes hyperpolarization whereas EPSP cause depolarisation. In the absence of neurotransmitter (ligand) the ion channel component of ligand receptor/ionotropic receptor remain CLOSED and when it get correct neurotransmitter then bind with the ionotropic receptor hence the ion channel will OPEN..which results into EPSP or IPSP in post synaptic neurons.

When excitatory ligand binds with the ionotropic receptor it acts as cation channel additionally it allow passage of Na+,K +and Ca​​​​​2+  through post synaptic cell membrane...where sodium ions influx is greater than either calcium ions or potassium ions outflow.. result into depolarisation of postsynaptic cell membrane....For inhibitory neurotransmitter ,ionotropic receptor signal for chloride channel...when chloride channel open, large number of chloride influx occur in post synaptic cell ,it becomes hyperpolarised. (means most negative).

Example of ligand receptor signaling/ ionotropic receptors are Acetylcholine receptor,GABA receptor, Serotonin receptors etc

So the ligand receptor signaling, ion channel(gate )will OPEN only when it gets correct ligand( neurotransmitter) causes depolarisation or hyperpolarization otherwise Gate will be CLOSE in resting stage.