AJP - Endocrinology and Metabolism, Vol 258, Issue 3 E445-E450, Copyright © 1990 by American Physiological Society
Stimulation of porcine thyroid cell alkalinization and growth by EGF, phorbol ester, and diacylglycerol
N. Takasu, I. Komiya, Y. Nagasawa, T. Asawa, T. Shinoda, T. Yamada and Y. Shimizu
Department of Gerontology, Endocrinology, and Metabolism, School of Medicine, Shinshu University, Nagano-ken, Japan.
We studied the effects of epidermal growth factor (EGF),
12-O-tetradecanoylphorbol-13-acetate (TPA), and 1-oleoyl-2-acetyl-glycerol
(OAG) on cytoplasmic pH (pHi) and cell growth in cultured porcine thyroid
cells. pHi was measured using
2',7'-bis(2-carboxyethyl-5,6-carboxyfluorescein (BCECF), an internalized
fluorescent pH indicator. EGF, TPA, and OAG alkalinized the thyroid cells
and stimulated their growth. These EGF-, TPA-, and OAG-stimulated cell
alkalinization and growth depended on extracellular Na concentrations and
were inhibited by amiloride, an inhibitor of Na(+)-H+ exchanger, indicating
that EGF-, TPA-, and OAG-stimulated cell alkalinization and growth may
occur through activation of Na(+)-H+ exchange. Alkalinization seems to be
involved in thyroid cell growth. TPA (a tumor-promoting phorbol ester) and
OAG (synthetic diacylglycerol), both potent activators of protein kinase C,
imitate the action of EGF in rapidly elevating pHi and stimulating cell
growth in thyroid cells. Trifluoperazine, an inhibitor of protein kinase C,
inhibited EGF-, TPA-, and OAG-stimulated cell alkalinization and growth.
The data suggest that activation of protein kinase C may be involved in the
mechanism of EGF-stimulated cell alkalinization and growth of the thyroid
cells.
