Question

As part of a pathophysiology lecture in a fourth year course, you are informed that two different types of G-protein coupled receptors are expressed on a human organ system. The activation of receptor-1 (R-1) causes an elevation in cyclic adenosine monophosphate (cAMP) levels in the cells. While the activation of receptor-2 (R-2) causes an inhibition in the rise of cAMP levels in the same cells.

Q1. Which G-protein alpha subunit is most likely associated with R-1 and R-2? 2 points R-1 = Q2.

You are further informed that activation of R-1 causes relaxation of smooth muscles in the organ expressing these receptors.

What do you think could be the possible effect of R-2 activation? 1 point

Q3. If the pathophysiology (clinical problem) in patients is excessive muscle contraction and constriction of the tissue, how can you target these two receptors to correct the underlying disorder? Note: Think in terms of agonist/antagonist for receptors R-1 and R-2. 2 points

Answer 1

Q.1ans:

Many membrane bound receptor produce response through the activation of G protein.

G protein have mainly three sub-unit i.e.alpha, beta,gamma

G protein is in active state whenGTP bounded to alpha sub-unit.

In above case two receptor are discuss. R1 and R2.

R1 elevate the cAMP level in cell, and cause relaxation of smooth muscle

R1- Gs receptor

R2- cAMP inhibition(only one receptor)

R2-Gi receptor

Q.2ans:

R1-alpha 1

R2-alpha2

Effect of R2 activation:

Decreases sympathetic flow,

increases insulin secretion,increases glucose uptake, decreases lipolysis in fat cell

Q.3ans:

GPCReceptor

Gs: beta adrenergic receptor,histamine,serotonin.

Gi: alpha2 adrenergic receptor,opioid, serotonin.

DRUG USED:

increase in cAMP inhibit contraction. there for drug should be Gs agonist. and gi antagonist:

Gs agonist; adenosine,prostacyclin

Gi antagonist:Yohimbine

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