Receptor theory 1

Question 1

What are the two principle theories of neurotransmission?

Answer 1

The electrical and humoral theory.

Question 2

What is the electrical theory of neurotransmission?

Answer 2

Electrical current from a large muscle mass may excite a nerve. The effect should be bidirectional, however the current in the nerve is too small to excite a muscle so amplification is required. This amplification occurs at the nerve/muscle junction and is achieved chemically.

Question 3

What is the humoral (chemical) theory of neurotransmission?

Answer 3

Transmission across the gap is uni-directional and there is delay in transmission across the gap. Fatigue occurs more readily at junctions. Drugs can act selectively at synapses/junctions.

Question 4

What studies did Henry Dale do?

Answer 4

Histamine and acetylcholine.

Question 5

What does ACh mimic?

Answer 5

Parasympathetic nerve stimulation (decreased heart rate).

Question 6

What was ACh found to be equipotent with?

Answer 6

Muscarine.

Question 7

What are low doses of ACh blocked by?

Answer 7

Atropine.

Question 8

What do high doses of ACh mimic?

Answer 8

Nicotine - stimulation of the sympathetic ganglionic cells.

Question 9

What did Otto Loewi do?

Answer 9

Provided the first evidence of chemical transmission.

Question 10

What experiments did Otto Loewi do?

Answer 10

Frog heart experiments - showed that Vagusstoff was released from nerve endings and was transferred to another heart through a water pump. He did a second experiment where he stimulated the accelerans nerve to show the heart rate of heart 1 increased, followed by heart 2.

Question 11

What is a pharmacodynamic interaction?

Answer 11

Interaction between a drug and biological recognition system to achieve a change in organ function.

Question 12

What is a receptor?

Answer 12

A macromolecule with with a drug combines to produce its characteristic effects.

Question 13

What are the 4 kinds of drug targets?

Answer 13

Enzymes, carrier molecules, ion channels and receptors.

Question 14

What is affinity?

Answer 14

If a molecule closely associates with a receptor it is described as having affinity for this receptor.

Question 15

How can the result of a drug-receptor interaction be measured?

Answer 15

Plotting the concentration of a drug vs. the response (such as smooth muscle contraction).

Question 16

What is the best way to plot the result of a drug-receptor interaction?

Answer 16

The % maximum response against the log of the drug concentration.

Question 17

What is the pEC50?

Answer 17

The negative log drug concentration to reach a 50% maximal response.

Question 18

What is intrinsic efficacy?

Answer 18

Different molecules having different capabilities to induce the physiological response.

Question 19

What are antagonists?

Answer 19

Drugs that bind to a receptor but elicit no response themselves and block the responses that are induced by agonists.

Question 20

What properties do antagonists have?

Answer 20

Affinity for the receptor, but no intrinsic efficacy.

Question 21

Why is it difficult to measure the potency of antagonists?

Answer 21

They have no efficacy themselves - need to measure their potency by relying on their ability to blocking agonists and measuring this.

Question 22

What is a competitive antagonist?

Answer 22

An antagonist that competes for the same binding site as the agonist.

Question 23

What are partial agonists?

Answer 23

Compounds that exhibit some agonist activity but do not elicit full responses, and block responses induced by full agonists.

Question 24

What is a strong partial agonist?

Answer 24

Strong agonist, weak antagonist.

Question 25

What is a weak partial agonist?

Answer 25

Weak agonist, strong antagonist.