Effects of wortmannin upon the late stages of the secretory pathway of AtT-20 cells

Heterotrimeric GTP-binding (G) proteins, termed Ge. have a role in the late stages of the adrenocorticotrophin (ACTH) secretory pathway in the mouse A tT-20/D16-16 anterior pituitary tumour cell line. The wortmannin sensitivit y of Ge-controlled mechanisms in AtT-20 cells was investigated to provide i nformation on the possible mechanisms linking Ge with secretion. Permeabili sed cells exposed to calcium ions(10(-9) to 10(-3) M), guanosine 5'-O-(3-th iotriphosphate) (GTP-gamma -S)(10(-8) to 10(-4) M) and mastoparan(10(-8) to 10(-5) M) demonstrated a significant and concentration-dependent stimulati on of ACTH secretion from non-stimulated levels for all three agents. Coinc ubation with wortmannin (10(-5) M) significantly inhibited both calcium-ind ependent and -stimulated secretion. The effect of wortmannin was concentrat ion-dependent being maximal at 10(-6) M. The study shows that wortmannin in hibits both calcium-independent and -stimulated secretion from permeabilise d AtT-20 cells indicating a role for phosphatidylinositol-3 kinase in deter mining the size of the readily releasable pool of ACTH and/or in mediating calcium/Ge-evoked secretion from this pool. (C) 2001 Elsevier Science B.V. All rights reserved.