Dopamine-D2S receptor inhibition of calcium influx, adenylyl cyclase, and mitogen-activated protein kinase in pituitary cells: distinct Galpha and Gbetagamma requirements

Mol Endocrinol. 2002 Oct;16(10):2393-404. doi: 10.1210/me.2001-0220.


The G protein specificity of multiple signaling pathways of the dopamine-D2S (short form) receptor was investigated in GH4ZR7 lactotroph cells. Activation of the dopamine-D2S receptor inhibited forskolin-induced cAMP production, reduced BayK8644- activated calcium influx, and blocked TRH-mediated p42/p44 MAPK phosphorylation. These actions were blocked by pretreatment with pertussis toxin (PTX), indicating mediation by G(i/o) proteins. D2S stimulation also decreased TRH-induced MAPK/ERK kinase phosphorylation. TRH induced c-Raf but not B-Raf activation, and the D2S receptor inhibited both TRH-induced c-Raf and basal B-Raf kinase activity. After PTX treatment, D2S receptor signaling was rescued in cells stably transfected with individual PTX-insensitive Galpha mutants. Inhibition of adenylyl cyclase was partly rescued by Galpha(i)2 or Galpha(i)3, but Galpha(o) alone completely reconstituted D2S-mediated inhibition of BayK8644-induced L-type calcium channel activation. Galpha(o) and Galpha(i)3 were the main components involved in D2S-mediated p42/44 MAPK inhibition. In cells transfected with the carboxyl-terminal domain of G protein receptor kinase to inhibit Gbetagamma signaling, only D2S-mediated inhibition of calcium influx was blocked, but not inhibition of adenylyl cyclase or MAPK. These results indicate that the dopamine-D2S receptor couples to distinct G(i/o) proteins, depending on the pathway addressed, and suggest a novel Galpha(i)3/Galpha(o)-dependent inhibition of MAPK mediated by c-Raf and B-Raf-dependent inhibition of MAPK/ERK kinase.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenylyl Cyclases / genetics
  • Adenylyl Cyclases / metabolism*
  • Animals
  • Calcium / metabolism*
  • Calcium Channels / metabolism
  • Cells, Cultured
  • Colforsin / pharmacology
  • GTP-Binding Protein alpha Subunit, Gi2
  • GTP-Binding Protein alpha Subunits, Gi-Go / genetics
  • GTP-Binding Protein alpha Subunits, Gi-Go / metabolism*
  • Heterotrimeric GTP-Binding Proteins / genetics
  • Heterotrimeric GTP-Binding Proteins / metabolism
  • Mitogen-Activated Protein Kinases / genetics
  • Mitogen-Activated Protein Kinases / metabolism*
  • Mutation
  • Pertussis Toxin / pharmacology
  • Pituitary Gland / cytology
  • Pituitary Gland / drug effects
  • Pituitary Gland / metabolism*
  • Proto-Oncogene Proteins / genetics
  • Proto-Oncogene Proteins / metabolism*
  • Rats
  • Receptors, Dopamine D2 / genetics
  • Receptors, Dopamine D2 / metabolism*
  • Thyrotropin-Releasing Hormone / metabolism
  • Thyrotropin-Releasing Hormone / pharmacology


  • Calcium Channels
  • Proto-Oncogene Proteins
  • Receptors, Dopamine D2
  • dopamine D2L receptor
  • Colforsin
  • Thyrotropin-Releasing Hormone
  • Pertussis Toxin
  • Mitogen-Activated Protein Kinases
  • GTP-Binding Protein alpha Subunit, Gi2
  • GTP-Binding Protein alpha Subunits, Gi-Go
  • Gnai2 protein, rat
  • Heterotrimeric GTP-Binding Proteins
  • Adenylyl Cyclases
  • Calcium