Spontaneous Intracellular Calcium Oscillations and G^sα Subunit Expression are Inversely Correlated with Secretory Granule Content in Pituitary Cells

Cells of the pituitary tumour cell line GH₄C₁ were exposed to epidermal growth factor, estradiol and insulin for 5 days, a treatment which resulted in 1) increased prolactin storage in secretory granules, 2) the loss of spontaneous [Ca²⁺]₁ oscillations, and 3) a selective reduction of the protein G_sα, seen in immunoblots, cholera toxin labelling, and vasoactive intestinal peptide stimulation of adenylyl cyclase. In contrast, the glucocorticoid dexamethasone, which increases the expression of G_sα, partially restored spontaneous [Ca²⁺]₁ oscillations and decreased prolactin storage. It is concluded that G_sα levels in tumoral cells result in spontaneous electrical activity which may empty prolactin stores by the continuous activation of exocytosis.