Ion channels Flashcards
What stimuli control ion channels’ gating?
- some channels respond to multiple stimuli
- temperature
- mechanical deformation
- membrane potential
- extracellular chemicals (taste, olfaction, neurotransmitters)
- intracellular second messangers (ATP, cAMP, Ca2+)
Voltage gated channels of the Kv, Nav, and Cav families have _____ membrane spanning domains, each with ______ alpha helices.
four membrane spanning domains; six alpha helices (S1 - S6)
What structures do the Nav and Cav channels contain?
- the four domains are linked into a single polypeptide
- S4 helices have positively charged residues (lys or arg) at every third position (sense voltage)
- S5 and S6 helices and the “P loop” (connects them) form the ion conducting pathway
What are ionotropic receptors?
neurotransmitter receptors are directly coupled to ion channels
What are pentameric ligand gated channels?
- ionotropic receptor
- lys-loop family of neurotransmitter receptor channels (GABAaRs, GlyRs, etc)
- heteropentamers
- each subunit has four transmembrane alpha helices (M1 and M4)
- M2 assembles around the central, ion-conducting pathway
- channels are selective for permeation of chloride, or allow both sodium and potassium
CLC chloride channels
- has an ion permeation pathway
- each permeation pathway can gate open and closed independently of one another
- some in this family are H+/Cl- exchangers
- important for stabilizing the resting membrane potential
Aquaporin water channels
- tetramers where each subunit contains a permeation pathway for water molecules
- anti-ion channels since they exclude all ions including protons
- e.g. in kidney
Which channels are selective? (Kv, Cav, Nav)
Kv and Cav are selective. Nav is moderately selective
How is charge important for what passes through a channel?
- channels are cation or anion selective
- ionic valence is also important
How are ions dehydrated in order to pass through a channel pore?
- ion is stabilized within the pore by energetic interactions with the amino acids forming the pore (but not completely or they would get stuck)
What is one factor that can increase channel pore selectivity?
if an ion interacts with multiple sites while traversing the channel pore
Describe the gating for Kv.
- the activation gate (intracellular side) can rotate around a center pivot point
- rotation is controlled by a “voltage-sensing” charge
- closed when cell has negative potential (deactivation)
- open when the inside is made positive causing K+ ions to flow out of the cell (called activation)
Describe Nav’s activation gate.
- on intracellular side
- closed at negative potentials
- open when the cell becomes positive and Na+ flows in
Describe Nav’s deactivation gate.
- on intracellular side
- open at resting potential (activation gate occludes access to a site within the inner end of the pore at which the inactivation gate can bind)
- after the activation gate opens, the inactivation gate closes (called inactivation)
Describe the selectivity filter for Kv and Nav.
occurs within a central, ion conducting pathway formed by the four Kv subunits or four repeats of Nav (central pathway surrounded by S5 and S6 helices and connecting P loop)
