usmlegr
Forum Junior
Topics: 6
Posts: 56
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Heart: β1->Gs->AC-> raise in cAMP-> raise in Ca++ -> Chronotropic/Inotropic action (through the raise of Ca++)
Vessels: β2->Gs->AC-> raise in cAMP-> X -> Relaxation of smooth muscle.
What is X?
How can 2 signalling systems both bind to Gs, raise cAMP, raise Ca++ and the one causes Inotropic action and the other Muscle relaxation?
(Opie, in "Drugs for the Heart" 6th ed ,2005, states that in heart β2 bind equally to Gs and Gi)
Any insight?
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| cyra
Moderator
Topics: 29
Posts: 844
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X in case of B2 receptors would be activation of protein kinase A via increased cAMP...
Protein kinase A would phosphorylate myosin light chain kinase(MLCK) thereby inactivating it.(MLCK is responsible for phoshporylation of myosin light chain which can then associate with actin and cause contraction.Once this is inactivated...relaxation occurs).
Am not so clear as to how exactly the B1 rec cause an increase in Ca though.....some input here would be great help!
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| usmlegr
Forum Junior
Topics: 6
Posts: 56
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Thank you cyra!
Here is the sequency of b1:
b1 activate via Gs the adenyl cyclase which in turn leads to increased cAMP formation. The latter activates protein kinase A which phosphorylates the calcium channel protein thus increasing the opening probability of the Ca++ channel. More Ca++ enter through the sarcolemmal channel which releases more Ca++ from the sarcoplasmic reticulum.
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