Prostaglandin F(2α) stimulates phosphatidylinositol 4,5-bisphosphate hydrolysis and mobilizes intracellular Ca²⁺ in bovine luteal cells

The present studies were conducted to determine whether prostaglandin F(2α) (PGF(2α)) stimulates the production of 'second messengers' derived from inositol phospholipid hydrolysis and increases intracellular free Ca²⁺ ([Ca²⁺](i)) in isolated bovine luteal cells. PGF(2α) provoked rapid (10 sec) and sustained (up to 60 min) increases in the levels of inositol mono-, bis-, and trisphosphates (InsP, InsP₂, and InsP₃, respectively). InsP₃ was formed more rapidly than InsP₂ or InsP after PGF(2α) treatment. In addition, PGF(2α) increased inositol phosphpholipid turnover, as evidenced by increased ³²PO₄ incorporation into phosphatidic acid and phosphatidyl-inositol. LiCl (1-20 mM) enhanced inositol phosphate accumulation in response to PGF(2α). Maximal increases in InsP₃ occurred at 1 μM PGF(2α), with half-maximal stimulation occurring at 36 nM. The acute effects of PGF(2α) on InsP₃ levels were independent of reductions in extracellular calcium. Prostaglandins E₁ and E₂ also stimulated increases in inositol phosphate levels, albeit to a lesser extent. PGF(2α) also induced rapid and concentration-dependent increases in [Ca²⁺](i) as measured by quin-2 fluorescence. The PGF(2α)-induced increases in [Ca²⁺](i) were maximal within 30 sec (approximately 2- to 3-fold), and [Ca²⁺](i) remained elevated for 8-10 min. The PGF(2α)-induced increases in [Ca²⁺](i) were also independent of extracellular calcium. These findings demonstrate that the action of PGF(2α) is coupled to the phospholipase C-InsP₃ and diacylglycerol second messenger system in the corpus luteum.