lec 9 Flashcards
Ionotropic receptors
Ligand-gated ion channels as opposed to voltage-gated ion channels that generate action potentials
Not necessarily cation specific
Nicotinic Ach receptor (ionotropic)
5 glycoprotein subunits
(2 alpha, 1 beta, 1 delta, 1 gamma)
Each subunit has 4 transmembrane segments (m1-m4)- m2 lines the pore
2 Ach molecules open the channel by binding to the alpha subunits- pore opens for 1 msec
GABA (A) receptor (ionotropic)
5 glycoprotein subunits
Each subunit has 4 transmembrane segments (M1-M4)- M2 lines the pore
2 GABA molecules open the channel by binding to the sites between the alpha and beta subunits
Opens for Chloride anions (Cl-)
Are all ligand-gated ionotropic receptors similar
Yes- except glutamate
Glutamate receptor
4 subunits
Each subunit has 3 transmembrane segments (m1,m3,m4)-m2 is a reentrant pore loop
Each subunit has a binding site- N terminal tail and extracellular loop between m3 and m4
Channel opens when two binding sites are occupied
3 main types of glutamate receptor
AMPA receptors
Kainate receptors
NMDA recptors
AMPA receptors (6)
Dimer means it consists of two identical subunits
Heterotetrameric
In most GluA2 is present, GluA1, GluaA3, GluA4
4 glutamate binding sites but channel opens with 2 bound
General cations channel- Na+, K+ pass freely
GluA2 prevents passage of Ca+
Kainate receptors
5 receptor subunits (GluK1-5)
Na+, K+ pass freely- low permeability for Ca+
Slower EPSPs compared to AMPA receptors
NMDA
3 subunits (GluN1-3) with many variants
Typically heterotetramers with 2 GluN1 and 2 GluN2 subunits
Open channel is permeable to Na+, K+, Ca 2+
2 glutamate (GluN2) and 2 glycine (GluN1) binding sites
Partially voltage dependent
Zinc ions, proteins and polyamines also have binding sites
Heterotetrameric
Meaning 4, not all the same
