Voltage gated channels Flashcards
How to isolate sodium channels
Replace intracellular potassium with caesium and add cadmium And tea to external
Sodium conductance characteristics
Activation Threshold -40 mV
Sigmoidal increase with voltage
Half Max -25 mV
Potentially what explains stimulus dependent decrease of nerve evoked EPSP?
Slow recovery from sodium channel inactivation
Time constant 20 ms accelerated with membrane hyper polarisation
What does ciguatoxin do to neuronal excitability?
Increases neuronal excitability and causes spontaneous opening of single sodium channels by shifting voltage of activation to more negative potentials
How do you isolate calcium channels?
Inhibit sodium currents with TTX or replace external sodium with an impermeable cation, and suppress potassium currents with intracellular caesium and/or extracellular TEA
The affect of barium on calcium channels
1.5 fold increase in current density
Calcium conductance characteristics
Activation threshold -30 MV, sigmoidal increase with depolarisation, Half max -5 MV
Effect of barium on calcium activation curve
Shifted 10 mV to more negative potentials
Which sodium channels are present?
TTX sensitive Nav1.1-1.3,1.7
Which types of calcium channels are present?
L, N, P/Q and R
What’s the L type molecular identity and antagonist?
Cav1.2 and Dihydropyridines (eg nifedipine)
What is the N type molecular identity and antagonist?
Cav2.1 and omega conotoxin gvia
What is the PQ identity and antagonist?
Cav2.2 and omega conotoxin mviic
What is R type identity and antagonist?
Cav2.3 and nickel ions
What potassium channels are present?
Kv, A, BKCa, AHP, Kir, Katp, M
What is the Kv type identity and antagonist?
Kv1.5,1.6, and TEA, verapamil
What is that IA type identity and antagonist?
kv3.x, kv4.x, 4 aminopyridine
What is the AHP antagonist?
Ryanodine
What is the KiR identity and antagonist?
Kir2.x, Kir3.x, Barium
What is the KATP identity and antagonist?
Kir6.x/Sur1-2, glibenclamide
What is the M type identity and antagonist?
KCNQ1-5, XE991 (linopirdine)
What is the H type identity and antagonist?
HCN1-4, caesium etc
Main calcium channel which is target different neuro transmitters?
N type
What is IKv called and what is its function?
Delayed outward rectifier, terminate action potential rapidly.
Delayed outward rectifier conductance characteristics
Activation threshold -40 mV, increase with voltage until saturation about 20 mV
What is the Potassium current IA called and what is its function?
Transient outward current, activated in sub threshold range of neuronal excitation and functions to reduce the excitatory effects of depolarising stimuli by decreasing rate of decay of AHP
What are the effects of 4-AP?
Inhibits transient outward current IA responsible for AHP decay, increase firing frequency
What is iKca and what is it function?
Calcium dependent potassium current , Hyperpolarise cell after burst of action potentials sufficient to raise intra cellular Calcium
What is Ikir and what is its function?
Inward rectifying current, hyperpolarisation activated. Outward current blocked by intracellular magnesium. Maintain resting membrane potential
What is iKca and what is it function?
Calcium dependent potassium current , Hyperpolarise cell after burst of action potentials sufficient to raise intra cellular Calcium
What is IkATP and what is it function?
ATP sensitive potassium current, transduce changes in cell metabolism to membrane potential. Open at low ATP concentration.
What is IM and what is it function?
Muscarine sensitive, noninactivating potassium current. Partially activated at rest. ACh evokes slow depolarisation associated with increased membrane resistance and decreased outward current resulting from inhibition of IM.
