Actions of Drugs on Ion Channels

Question 1

Voltage dependant ion channels?

Answer 1

• Ion channels are membrane proteins that conduct ions passively across the membrane, under the influence of an electrochemical gradient
• Two major groups:
  
  • Voltage dependant
  • Ligand dependant

Question 2

Voltage dependant ion channels enable a cell to be excitable, ie generate action potentials. Named according to which ion they conduct.

Answer 2

• Calcium channels - 10 different alpha subunits genes
• Potassium channels - 40 different alpha subunits - produces incredible complexity: few drugs target this channel
• Sodium channels - 9 different alpha subunit genes. Local anaesthetics, antidysrhythmics and anti-epileptic agents target this channel

Question 3

Voltage Dependant Calcium channels in the Cardiovascular system?

Answer 3

Question 4

The Dihydropyridines Calcium Channel Antagonists?

Answer 4

Question 5

Answer 5

Question 6

Monoamine Transporter Molecules at a synapse?

Answer 6

• Cells need to activelytransport many substances across their membranes: Targeting transport mechanisms forms the therapeutic basis of action of many drugs
• Monoamines noradrenaline, 5-HT and dopamine are important neurotransmitters
• Each has its owntransporter
• Can terminate their action at synapse by blocking their terminal

Question 7

The tricyclics (TCAs) have been in clinical use for 60 years, (Clomipramine inhibit both NET and SERT). What are the usual side effects?

Answer 7

• Antagonism of muscarinic ACh receptors common in the peripheral autonomic system
• Causes cardiac dysrhythmias
• Dry mouth
• Blurred vision
• Constipation

Question 8

Serotonin/noradrenaline reuptake inhibitors (SNRIs), such as venlafaxine are relatively non selective for NET and SER. Side FXs?

Answer 8

• Favourable side fx profile
• Do not have any antmuscarinic effects
• Most commonly px antidepressants (fluoxetine)