test 2 lec 2 part 1 Flashcards
depolarization part 2
Two major types of Voltage- dependent Ca2+ channel based on their kinetics?
LVA, HVA
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LVA VDCCS
Rapidly inactivating, low-voltage activate _ activate by a small amount of depolarization
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T-channels
they are LVA channel that produce a transient current
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_ HVA (high-voltage activated)
activate by a large amount of depolarization. There are 2 categories based on their inactivation:
1- Inactivating
2-Non-inactivating (or more slowly inactivating)
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single Vs whole cell current
single cell recording is a single ion channel under the electrode tip
Whole cell recording is the current of something approximating the entire cell
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which way is Ca2+ current
inward or downward deflection
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when does LVA channels turn on and off?
Turned on right around resting potential and peak current flow occurs at well below zero (hit their peak at negative potential.), then starts to turn off as action potential becomes stronger and moves past the 0 potential
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when does HVA channels turn on and off?
o Takes more depolarization to turn on, and won_t reach its max until somewhere well above zero.
o Right where the downslope of the LVA ends, the HVA peaks
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in I/V graph which way is the graph shifted by turning on HVA channels?
Rightward shifted on I/V curve.
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IV curves
it is a current/voltage curves, it shows the relationship of the curent vs voltage of a cell, Voltage is on the x-axis
o We can find resting potential and 0 potential and positive potential in unit of Voltage (V)
_ Hyperpolarize moves to the left
_ Depolarize moves to the right
o Current is on the Y-axis (measure of current in unit of Amp)
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what is the name of non-inactivation HVA channel?
o L-type channels
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o L-type channels
found in Cardiac and neuronal tissue, _ Non-inactivating: takes a lot of depolarization to turns on, and as long as cell remains depolarized, it stays activated, can be blocked by cadmium and can be restored to its original condition by washing out the blocker
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what are some of the slow-inactivation HVA channels:
o N-type channel, o P-type channels, o Q-type channels, o R-type channels
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o N-type channels
_ Slow-inactivating (SI)
_ Very common in neurons
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o P-type channels
_ Pre-synaptic & post-synaptic axon terminals
_ Slow-inactivating
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o Q-type channels, or PQ type channel
_ Basically exactly P-type channels with 1 amino acid difference
_ Slow-inactivating
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o R-type channels
_ Slow-inactivating
_ Found in Neuron
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o T- type channels
_ Expressed in most neurons and cardiac muscle
_ FI _ fast inactivating _ doesn_t take much of depolarization to turn in on, but it turn off fairly quickly
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what are some of the Organic Ca2+ channel toxin sources?
_ Spiders, snakes, plants, microorganisms
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_ L-type Ca2+ channel blockers?
Dihydropyridine, Arylalkylamine, Benzothiazepine, Alkaloids
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Nifedipine
it is under Dihydropyridine category and it is regularly prescribed for people with severe hypertension (lower BP); heart patients with cardiac problems
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Nimodipine
it is under Dihydropyridine category and it is better for neuronal effects; specific effects on cerebral blood vessels (associated with the brain); better at crossing BBB than Nifedipine
Originally Designed to increase cerebral blood flow
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Verapamil
Arylalkylamine (synthetic)
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Diltiazem
it is under Benzothiazepine (synthetic)category and it is widely prescribed for blood pressure and cardiac problems.
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what are some of the T-Type Ca2+ channel blocker? What is their effect?
it is chemically called Benzimidazole (synthetic) and vasodilation is its effect
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Flunarazine
it is a T-type channel blocker and under Benzimidazole category, it is also the safest one to use for Vasodilation
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N-type channel blockers
_ _-CTX-GVI(6)A _ the most potent Conotoxin to block N-type Ca2+ currents.
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Ca2+ channel blockers II
_ P/Q-type channel
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P/Q-type channel blockers
o Agatoxins (FTX) (comes from funnel web spider) called _ -Aga-Ia (most commonly used), _ Blockers for all Ca2+ channels
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_ R-type blocker
no good specific R-type blocker, so you must block all in order to block R-type
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o Inorganic ions blockers of Ca2+ channels
_ Cadmium, Mg2+ _ Cd2+ _ Cs2+ _ Ni2+
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Mg+ is smaller that Ca2+, but how come it can block Ca2+ channels?
because of the particular AA residue that make up the pore of the channel, and their relative charge location and how it interacts with these ions of different ionic radius
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what is Barium ions used for?
preferred charge carrier for Ca2+ current experiments (it is basically a good substitute for Ca2+) because it doesn_t cause secondary effects
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what are side effect of using Ca2+ in the experiment?
There are a lot of Ca2+ sensitive enzyme systems in the body, so a lot of different things can happen when Ca2+ come in, but this is not true for Barium.
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what is a L-type Ca2+ channel activator (agonists)?
BAY-K-8644 (DHP class)
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what are the features of BAY-K-8644?
It just facilitates the opening of the channels when membrane is depolarized (it doesn_t activate the channel by it self, it just opens it for a longer time when voltage activates the channel
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what is one kind of toxin that can facilitate all types of Ca2+ channels?
o Maitotoxin (peptide class)
