Figure 5.15 and 5.21

5.15  Transmitter actions at G-protein-coupled receptors.  The binding of neurotransmitter to the receptor leads to the activation of G-proteins.  Activated G-proteins activate effector proteins, which may be (a) ion channels or (b) enzymes that generate intracellular second messengers.

Figure 5.21  Modulation by the NE b receptor. (1) The binding of NE to the receptor activates a G-protein in the membrane.  (2) The G-protein activates the enzyme adenylyl cyclase.  (3) Adenylyl cyclase converts ATP into the second messenger cAMP.  (4)  cAMP activates a protein kinase.  (5) cAMP kinase causes a potassium channel to close by attaching a phosphate group to it.

NE = norepinephrine