Neuronal Ionic Currents Flashcards
different current types based on the ion channel
Transient; rapidly activating and inactivating; current has large amplitude
Fxn: Generates APs
Na+
INa or INA,t
Persistent; rapidly activated by depolarizations like synaptic potentials but most importantly non-inactivating; current has smaller amplitude
Fxn: Enhances Depolarization from Excitatory inputs - may result in Plateau Potentials; contributes to steady-state firing
This current’s amplitude and cellular distribution has an important role in determining the responsiveness of neurons - it contributes to the baseline firing rate of neurons (pacemaker activity).
Na+
INA,p
Transient; rapidly inactivating; threshold for activation around -65mV (below standard AP threshold)
Fxn: generates rhythmic burst firing of APs
Through activation & inactivation of this current, neurons can generate slow Ca2+ spikes, which result in the generation of a high-frequency “burst” of short-duration Na+/K+ APs - because of their prolonged duration. Ex: thalamic relay neurons.
Ca2+
IT, low threshold
Long-lasting current; slowly inactivating; high-threshold for activation, around -20mV
Fxn: Underlies Ca2+ spikes that are prominent in dendrites; involved in synaptic transmission
High-voltage Activated (HVA); blocked by dihydropyridines (its antagonist)
Ca2+
IL, high threshold
Neither; rapidly inactivating; threshold around -20mV; modulated by a variety of neurotransmitters
Fxn: Underlies Ca2+ spikes that are prominent in dendrites; involved in synaptic transmission
High-voltage Activated; not blocked by dihydropyridines; blocked by conotoxin-GVIA; involved in the Ca2+ dependent release of neurotransmitters in the presynaptic terminals of some cell types.
Ca2+
IN
Purkinje; threshold around -50mV; these channels do not inactivate
Fxn: Generate Ca2+ spikes that are prominent in dendrites, strongly modulates firing pattern of neuron
High-Voltage Activated (HVA); not blocked by either dihydropyridines or conotoxin-GVIA; blocked by Agatoxin-BIA
Ca2+
IP
Activated by strong depolarization positive to -40mV; slow inactivation
Fxn: repolarization of APs and subsequent hyperpolarization
“Delayed-rectifier” bc the activation kinetics are slower than the transient Na current and therefore appear delayed.
K+
IK
Activated by increases in [Ca2+]i; rapid inactivation once membrane is repolarized
Fxn: AP repolarization and interspike interval
Calcium-Activated Potassium Current (1 of 2); voltage-dependent; controls freq. of AP generation during a steady depolarization by causing a marked hyperpolarization after the occurrence of each spike; contributes significantly to short spike intervals, due to its short time course.
K+
IC
Slow afterhyperpolarization; sensitive to increases in [Ca2+]i
Fxn: Slow adaptation of action potential discharge; the block of this current by neuromodulators enhances neuronal excitability
Calcium-Activated Potassium Current (1 of 2); not very voltage-dependent; slower in time course than IC; influences membrane potential mainly after a number of APs as a prolonged afterhyperpolarization; contributes significantly to the tendency of the firing freq. of some types of neurons to decrease during maintained depolarizations (spike freq. adaptation).
K+
IAHP
Transient; rapidly inactivating
Fxn: delayed onset of firing; lengthens interspike interval; AP repolarization
“Transient Potassium Current”; serves to delay the onset of the first AP; can also slow a neuron’s firing freq during maintained depolarization
K+
IA
muscarine sensitive; activated by depolarization of membrane to approx -65mV; non-inactivating
Fxn: contributes to spike frequency adaptation; the block of this current by neuromodulators enhances neuronal excitability
“Muscarine-sensitive Potassium currents”; blocked by stimulation of muscarine cholinergic receptors
K+
IM
Depolarizing (mixed cation) current that is activated by hyperpolarization
Fxn: contributes to rhythmic burst firing and other rhythmic activities
“Currents activated by hyperpolarization”; subsequently brings membrane potential back towards rest; the current in this family are carried by both Na and K ions; relatively slow in time course; activation results in slow depolarization of the cell, which generates a “pacemaker” potential that can activate repetitive Na and/or Ca2+ spikes.
K+
Ih
contributes to neuronal resting membrane potential
Fxn: the block of this current by neuromodulators can result in a sustained change in membrane potential
K+
IK,leak
