May 05, 2015

Concerning Receptors and their Mechanisms of Action


Concerning receptors and their mechanisms of action. The main autonomic receptor types and postreceptor mechanism may vary from one tissue to another.

Select the correct match of receptor / tissue / postreceptor mechanism for the following tissues:

a) M2 / heart / opening of ligand-gated calcium channels
b) Nm / skeletal muscle endplate / increased IP3 and diacylglycerol
c) Alpha-2 / smooth muscle and glands / decrease of camp
d) Beta-2 / smooth muscle / increased cAMP
e) Dopamine-1 / smooth muscle / increased IP3 and diacylglycerol


The correct answer is D


M2 is found in the heart. But it does not work via ligand gated calcium channels. It works through the Gq protein leading to the pathway of IP3 and diacylglycerol.

Nm is found in skeletal muscle endplate. But it does not work via increased IP3 and diacylglycerol. It’s a ligand gated calcium channel.

Alpha-2 is not found in smooth muscles and glands. It works by inhibiting AMP cyclase via Gi protein.

Dopamine-1 is found in smooth muscles. But it works on Gs proteins, thus increasing cAMP instead of increasing IP3 and diacylglycerol. That leaves us with one answer, which is D.

Beta-2 is found in smooth muscles. It works on the Gs protein, increasing the cAMP levels

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