Muscarinic regulation of Ca2+ oscillation frequency in GH3 cells.
The GH3 anterior pituitary cell line has been used as a model to investigate diverse aspects of pituitary cell physiology including Ca2+ homeostasis and secretion. These cells possess muscarinic receptors which, by activating K+ channels and inhibiting Ca2+ channels, should decrease electrical excitability. We measured the effect of carbachol (10 microM) on the frequency of Ca2+ oscillations caused by Ca2+ action potentials in the plasma membrane. Carbachol reduced oscillation frequency by approximately 85% (p < 0.001). This inhibition was reversed by atropine (1 microM), and was prevented by pre-incubation with pertussis toxin (200 ng/ml, 24 h). Since many anterior pituitary cell types secrete acetylcholine, the presence of muscarinic receptors coupled to cell excitability in these cells suggest that ACh could exert a paracrine- or autocrine-like action in GH3 cell cultures. In experiments designed to test this idea, perfusion with 1 microM atropine caused a small but significant increase (p < 0.05) in oscillation frequency when the cells had previously been incubated for 30 min without perfusion. However, this effect was not blocked by either pre-treatment with pertussis toxin or by including atropine during the entire experiment (including the 30-min incubation without perfusion). We conclude that these cells respond to muscarinic agonists by decreasing oscillation frequency but find no evidence for feedback control by endogenous ACh under these conditions.
Kushmerick
C
C
Departamento de Farmacologia, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil. chris@mono.icb.ufmg.br
Romano-Silva
M A
MA
Gomez
M V
MV
Prado
M A
MA
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D001285:Atropine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002478:Cells, Cultured; D018679:Cholinergic Agonists / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000187:drug effects / Q000378:metabolism; D018727:Muscarinic Antagonists / Q000494:pharmacology; D037342:Pertussis Toxin; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000378:metabolism*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D018679:Cholinergic Agonists; D018727:Muscarinic Antagonists; D011976:Receptors, Muscarinic; D010566:Virulence Factors, Bordetella; D001285:Atropine; D002217:Carbachol; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D002118:Calcium