Ion channels

Question 1

Membrane excitability

Answer 1

• an action potential leads to the opening of sodium or calcium channnels and later the opening of potassium channels
• At cells maintain a resting pontetial between -30 mv and - 80 mv

Question 2

Control of calcium and calcium entering mechanims

Answer 2

Control:

Entry; active transport mechanisms

Extrusion; ion channels

Exchange: active transport mechanisms and ion channels

Levels of calcium are controlled by stim 1 which promotes Ca2+ uptake when stores are completed

Question 3

Ways in which drug moleules can affect ion channel function

Answer 3

• directly binding to orthostertic or allosteric sites
• indirect activation i.e. via a GPCR
• Changes in gene expression

Question 4

Pharmacological modifcation of A.P

(think of examples)

Answer 4

Question 5

Contraction in skeletal and cardiac muscle

Answer 5

• Cardiac: Calcium entry through VGCC initiates Ca release through activation of calcium sensitive RyR
• Skeletal: RyR activated via a voltage dependent physical interaction
• Ca2+ binds to troponin which moves the tropmyosin chain out of the way

Question 6

Three ways which Calcium can trigger release of signalling molecules

Answer 6

1. Exocytosis i.e. ACH
2. Increased activity of NOS and difussion of NO
3. Cleavage of PIP2 to form Prostoglandins

Question 7

Molecular Structure and Functional properties of VGCC

Answer 7

• inactivating appendage between the fourth and fifth units
• pore forming areas between the 5 and 6 TM domain o feach unit
• Basic amino acid voltage sensing region in the fourth TM region

Question 8

Cys-Loop channels

Molecular structure and function

Answer 8

• pentameric assembly of a,b,gama, or sigma subunits
• binding sites lay at interface adjacent to alpha subunits
• binding of one molecule to one site increases affinity at the other
• each TM domain contains 4 membrane spanning a-helices which rotate to allow conformational change and ionic influx

Question 9

structure of other types of ligand gated ion channels

Answer 9

• iontropic glutamate receptors have a pore built from loops rather than TM domain
• P2X have a terameric assembly
• NMDA receptors have up to 4 agonist binding sites
• P2X have three but can open when two are bound