10 Biochem 2 - Contractility

Question 1

What is Ca2+ important for?

Answer 1

Contraction
Reaction cofactor
Enzyme regulation
Channel regulation
Second messenger
Apoptosis

Question 2

What does an uncontrolled release/build up of calcium lead to?

Answer 2

Super excitable contraction
Apoptosis

Question 3

Describe the Na+ Ca2+ exchange pathway

Answer 3

NCX uses the energy in the Na+ gradient set up by Na+ K+ ATPase to pump Ca2+ out of the cell

Question 4

Why is Na+ Ca2+ exchange an example of secondary active transport?

Answer 4

Doesn’t directly use atp to remove Ca2+

Question 5

How many Na+ come into the cell for every one Ca2+ that goes out? And how does this affect the net charge for the cell?

Answer 5

3
Net charge is +1

Question 6

How can NCX trigger depolarisation? And what does this lead to

Answer 6

Major contributor to the recovery of Ca2+ levels but can trigger depolarisation due to a Na+ influx
Ectopic contractions

Question 7

What is the funny current modulated by

Answer 7

ANS

Question 8

How does the sympathetic system enhance heart rate?

Answer 8

Increases influx of Na+ so increases rate of depolarisation
Increases amount of cyclic nucleotides HCN channels - mainly Na+ channels
Increases If - funny current

Question 9

How does the parasympathetic system slow heart rate?

Answer 9

Increases K+ current so slows depolarising affect of Na+ current
Girk/kir IKACH
Increases potassium efflux

Question 10

How does the sympathetic system increase force of contraction

Answer 10

PKA
1. Activates L type Ca2+ channels - Increases Ca2+ influx
2. Activates phospholamban - more rapid Ca2+ uptake to SR
3. Sensitises contractile proteins to Ca2+ - increased force of contraction
All lead to increased force of contraction

Question 11

What is a positive luistoropic effect

Answer 11

Increased rate of myocardial relaxation due to more rapid reuptake of Ca2+ to SR by SERCA

Question 12

What is positive dromotropic effect?

Answer 12

Increased conduction velocity through purkinje fibres

Question 13

What are the four effects of a sympathetic drive on the myocardium

Answer 13

Positive chronotropic effect
Positive ion tropic effect
Positive luistropic effect
Positive dromotropic effect
All lead to shorter but larger contraction controlled by Ca2+

Question 14

What happens in ventricular myocytes under parasympathetic drive?

Answer 14

Negative chronotropic effects
Ionotropic effects may be reduces
Negative luistropic effect
Negative dromotropic effect
Lead to longer duration but smaller contraction controlled by Ca2+

Question 15

What is preload

Answer 15

Myocardial stretch from venous return