Electrical and Molecular Mechanisms

Question 1

HCN channels

Answer 1

Hyperpolarisation activated cyclic nucleotide gated channels

Question 2

Plasma K+ concentration

Answer 2

3.5 - 5.5 mmol/L

Question 3

Mild, moderate and severe hyperkalaemia values

Answer 3

Mild 5.5 - 5.9 mmol/L
Moderate 6.0 - 6.4 mmol/L
Severe > 6.5 mmol/L

Question 4

Treatment for hyperkalaemia

Answer 4

Calcium gluconate

Insulin and glucose

Question 5

Effects of hypokalaemia

Answer 5

Lengthens the action potential

Question 6

Problem with hypokalaemia

Answer 6

Can lead to early after depolarisations (EADs)

Can result in ventricular fibrillation

Question 7

Excitation-contraction coupling

Answer 7

Ca2+ through T-tubules
CICR in SR
25% enters across sarcolemma, 75% released from SR

Question 8

Cardiac myocyte contraction

Answer 8

Ca2+ binds to troponin C

Tropomyosin shift to reveal myosin binding site on actin filament

Question 9

Myocyte relaxation

Answer 9

Most Ca2+ pumped back into SR via SERCA (raised calcium stimulates pump)
Some exits across cell membrane (sarcolemmal Ca2+ ATPase NCX)

Question 10

Excitation contraction coupling in smooth muscle cells

Answer 10

Depolarisation opens VGCCs
Ca2+ binds to CaM
Joins MLCK (myosin light chain kinase)
Phosphorylates myosin II head
MLCP (myosin light chain phosphatase) dephosphorylates myosin II head

Question 11

Phosphorylation of MLCK

Answer 11

By PKA

Inhibits the action of MLCK

Question 12

How long does a cardiac action potential last for?

Answer 12

280ml