TABLE 3.

SIGNAL TRANSDUCTION PATHWAYS FOR CATECHOLAMINE RECEPTORS

Receptor

G-Proteina

Effectorsb


Adrenergic

b1, b2

Gs

Adenylyl cyclase ( )

a1Ac

Gi/o

Ca2+ ( )

a1Bc

Gq

Inositol triphosphate ( )

a1Cc

Gq

Inositol triphosphate ( )

a1Dc

Gq

Inositol triphosphate ( )

a2A/Dd

Gi

Adenylyl cyclase ( ), K+ ( ), Ca2+ ( )

a2B

Gi2,3e

Adenylyl cyclase ( )

a2C

Goe

Adenylyl cyclase ( )


Dopaminergic

D1, D5

Gs

Adenylyl cyclase ( )

D2, D3, D4

Gi/o

Adenylyl cyclase ( ), K+ ( ), Ca2+ ( )

a

G-protein utilized by each receptor could vary depending on the brain region and effector systems present. Pertussis toxin has been useful in determining the type of G-protein utilized by different receptors: Gq and Gz are insensitive, while Gi and Go are inactivated by toxin treatment. Gz is not included in the Table: it is reported to mediate inhibition of adenylyl cyclase in cultured cells, but a role in mediating catecholamine receptor regulation of adenylyl cyclase has not been demonstrated.

b

The Table lists the primary action(s) mediated by G-protein a subunits. Different, and sometimes opposing, effects may be produced by G-protein bg subunits.

c

There are several cases of a-adrenergic stimulation of cGMP levels, presumably mediated via Ca2+ stimulation of nitric oxide synthase and subsequent nitric oxide stimulation of guanylyl cyclase.

d

a2A and a2D receptors appear to be human and rat homologues, respectively, with slightly different pharmacological profiles.

e

a2B and a2C prefer these G protein subtypes when expressed in cultured cells, but may utilize other G-protein subtypes in vivo.


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published 2000