Muscarinic regulation of Ca2+ oscillation frequency in GH(3) cells

The GH, anterior pituitary cell line has been used as a model to investigat e diverse aspects of pituitary cell physiology including Ca2+ homeostasis a nd secretion. These cells possess muscarinic receptors which, by activating K+ channels and inhibiting Ca2+ channels, should decrease electrical excit ability. We measured the effect of carbachol (10 mu M) on the frequency of Ca2+ oscillations caused by Ca2+ action potentials in the plasma membrane. Carbachol reduced oscillation frequency by approximate to 85% (p < 0.001). This inhibition was reversed by atropine (1 mu M), and was prevented by pre -incubation with pertussis toxin (200 ng/ml, 24 h). Since many anterior pit uitary cell types secrete acetylcholine, the presence of muscarinic recepto rs coupled to cell excitability in these cells suggest that ACh could exert a paracrine- or autocrine-like action in GH(3) cell cultures. In experimen ts designed to test this idea, perfusion with 1 mu M atropine caused a smal l but significant increase (p < 0.05) in oscillation frequency when the cel ls had previously been incubated for 30 min without perfusion. However, thi s effect was not blocked by either pre-treatment with pertussis toxin or by including atropine during the entire experiment (including the 30-min incu bation without perfusion). We conclude that these cells respond to muscarin ic agonists by decreasing oscillation frequency but find no evidence for fe edback control by endogenous ACh under these conditions. (C) 1999 Elsevier Science B.V. All rights reserved.