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BPK 306 > Excitation-Contraction Coupling > Flashcards

Excitation-Contraction Coupling Flashcards

1
Q

What is each myofibril surrounded by

A

Sarcoplasmic reticulum

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2
Q

What is a t-tubule, what does it do

A

T-tubules are invaginations of the sarcolemma that penetrate the fibre at junctions between the A/I bands in each half sarcomere

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3
Q

What is contained in the T-tubules

A

ECF- extra cellular fluid

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4
Q

What is part of the endomembrane system

A

SR

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5
Q

What does t-tubule stand for

A

Transverse tubule

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6
Q

What is contained in a triad

A

Two SRs about a T-tubule
SR cisterna/ t-tubule/ SR cisterna

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7
Q

What is the terminal cisternae and what is its importance

A

Region of SR nearest to the t-tubule (bulged end)
This is where excitation-contraction coupling begins

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8
Q

What causes the AP in postsynaptic cell

A

Opening of NAChR results in passive EPP where Nav channels open causing AP

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9
Q

Where are DHPR found and what is there actual name

A

L-type Ca channel
Localized to t-tubules

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10
Q

Where are RYR found and what are they coupled to

A

Localized to SR membrane
Mechanically coupled to DHPR

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11
Q

Where is Ca released from specifically

A

Terminal cisterna of SR

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12
Q

What is calsequestrin and where is it found

A

Is a calcium binding protein- reduces SERCA activity by decreasing Ca gradient
Low affinity for Ca- let’s go easily, needs high Ca to work
Found in SR- close proximity to RYR

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13
Q

What type of channel is DHPR

A

Cav1.1 (L-type)

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14
Q

What type of RYR channel

A

RYR1

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15
Q

What can summation of twitches produce

A

Unfused or fused tetanus

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16
Q

What is a twitch

A

Contraction and relaxation of muscle

17
Q

Explain time scale of events neuronal AP to muscle twitch

A

Neuronal AP- muscle AP- increase intracellular Ca and twitch starts- decreased Ca and twitch ends

18
Q

After end plate potential depolarizes to threshold explain the steps until Ca re-uptake after contraction

A
  1. Voltage gated Na channels open
  2. muscle AP spreads over sarcolemma and into T-tubules
  3. Muscle AP depolarization opens DHPR (L-type Ca channels)
  4. Mechanically coupled DHPR and RYR1 causes RYR1 to open and Ca release from SR
  5. Ca bind to TnC, after contraction Ca pumped back into SR by SERCA
19
Q

Explain physical set up on DHPR and RYR

A

4 Cav1.1 channels for 1 RYR
Every other RYR interacted with

20
Q

How are Cav1.1 and RYR1 physically coupled

A

Protein-protein interactions
Voltage induced conformational change in DHPR is transduced to RYR

21
Q

What are benefits to physical coupled DHPR and RYR vs Ca-induced Ca release

A
  1. Faster, more efficient- accelerate E-C coupling
  2. Don’t have to pump Ca back out of cell (NCX)- this reduces ATP consumption
22
Q

How are Cav1.1 channels grouped

A

Tetrads (4)
Seen in freeze fractures

23
Q

What is the “foot” a part of and where is it located

A

Each RYR1 has a foot that extends into cytosol

24
Q

Name specific thing that couples DHPR and RYR1

A

Specific amino acid residues in II-III linker
Linker interact with RYR1 foot

25
Q

What is Cav1.1 impact on contractility, what study proved this

A

No impact
Creates inward Ca current but when pore was blocked in mice contraction still fine due to physical coupling

26
Q

What are some Cav1.1 inhibitors and what are they used for

A

Dihyropyradine blocks channels
(ex. Nifedipine- antihypertensive for blood vessels)- DHP related
(ex. Verapamil- anti arrhythmogenic for cardiac) -not DHP related
Used to manage angina (chest pain), cardiac arrhythmia, high blood pressure, anti-hypertension

27
Q

SERCA function

A

Pump Ca against large concentration gradient
High density of pumps on SR membrane

28
Q

Is the cost of muscle contraction high or low

A

High metabolic cost

29
Q

Calsequestrin location and capacity

A

Within terminal cisternae- highly localized beneath triad junction
Has high capacity for Ca binding but low affinity

30
Q

How does calsequestrin aid in E-C coupling

A

Unloads Ca near RYR1 therefore allowing for SR Ca release

31
Q

Where does Ca bind for muscle contraction and how many

A

4 Ca bind to TnC- causes conformation change in TnI
2 high affinity binding sites that bind Mg2+ at rest
2 low affinity bind as Ca concentration rises
Also EF hands available- when Ca very low or very high

32
Q

What is moved to expose myosin binding site on actin

A

Tropomyosin

33
Q

Function TnT, TnI, TnC

A

TnT- binds tropomyosin
TnI- binds actin
TnC- binds Ca

34
Q

Force vs Ca concentration graph shape and 50%

A

Sigmoidal shape
Start 0.1 microM
50% max force at 1microM
Contractile force is Ca dependent

BPK 306 (18 decks)

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