Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0043167 (pertussis)
 19,595 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Experimental evidence exists for the presence of parathyroid cell membrane calcium channels that respond to plasma calcium. In previous reports, the effects of various calcium channel agents on PTH secretion have revealed conflicting results. To resolve some of these inconsistencies, we have compared the pure calcium channel agonist, (+)202-791, and its antagonistic enantiomer (-)202-791 with other calcium channel agents--verapamil, nifedipine, and (+)Bay-K-8644. The agonist (+)202-791 enhanced 45Ca+2 uptake and decreased PTH secretion, while the antagonist (-)202-791 decreased 45Ca+2 uptake and increased PTH secretion. The calcium channel appears coupled to a G-protein as indicated by pertussis toxin treatment of the cells. The enantiomers (+/-)202-791 had little effect on intracellular cAMP production suggesting that the calcium channel may not be responsible for the previously observed calcium-mediated changes in cAMP. The antagonist (-)202-791 increased the phosphorylation of a 60-kd protein. The enantiomers (+/-)202-791 did not alter the effect of depolarizing concentrations of potassium on PTH secretion. Our results suggest that calcium channels provide a pathway for the movement of calcium across the plasma membrane and that this pool of calcium regulates, at least in part, PTH secretion.
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PMID:Role of calcium channels in parathyroid hormone secretion. 754 1

Dopamine is the primary inhibitory regulator of lactotroph proliferation and prolactin (PRL) secretion in vivo, acting via dopamine D2 receptors (short D2S and long D2L forms). In GH4C1 pituitary cells transfected with D2S or D2L receptor cDNA, dopamine inhibits PRL secretion and DNA synthesis. These actions were blocked by pertussis toxin, implicating G(i)/G(o) proteins. To address roles of specific G(i)/G(o)4 proteins in these actions a series of GH4C1 cell lines specifically depleted of individual Galpha subunits was examined. D2S-mediated inhibition of BayK8644-stimulated PRL secretion was primarily dependent on G(o) over G(i), as observed for BayK8644-induced calcium influx. By contrast, inhibitory coupling of the D2S receptor to TRH-induced PRL secretion was partially impaired by depletion of any single G protein, but especially G(i)3. Inhibitory coupling of D2L receptors to PRL secretion required G(o), but not G(i)2, muscarinic receptor coupling was resistant to depletion of any G(i)/G(o) protein, whereas the 5-HT1A and somatostatin receptors required G(i)2 or G(i)3 for coupling. The various receptors also demonstrated distinct G protein requirements for inhibition of DNA synthesis: depletion of any G(i)/G(o) subunit completely uncoupled the D2S receptor, the D2L receptor was uncoupled by depletion of G(i)2, and muscarinic and somatostatin receptors were resistant to depletion of G(i)2 only. These results demonstrate distinct receptor-G protein preferences for inhibition of TRH-induced PRL secretion and DNA synthesis.
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PMID:G protein preferences for dopamine D2 inhibition of prolactin secretion and DNA synthesis in GH4 pituitary cells. 1214 43

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.
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PMID:Dopamine-D2S receptor inhibition of calcium influx, adenylyl cyclase, and mitogen-activated protein kinase in pituitary cells: distinct Galpha and Gbetagamma requirements. 1235 3