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Phloretin as an Antagonist of Prostaglandin F Receptor in Cultured Rat Astrocytes
Authors:Jun-ichi Kitanaka  Tadashi Ishibashi  Akemichi Baba
Affiliation:Department of Pharmacology, Faculty of Pharmaceutical Sciences, Osaka University, Suita, Japan
Abstract:Abstract: The effect of phloretin on prostaglandin (PG) F-induced phosphoinositide hydrolysis and elevation of intracellular Ca2+ concentration was examined in cultured rat astrocytes. Phloretin inhibited PGF (1 μ M )-induced phosphoinositide hydrolysis in a concentration-dependent manner with an IC50 value of 16 μ M . The inhibitory action of phloretin was specific for PGs. The addition of increasing concentrations of phloretin caused progressive shifts of the dose-response curves of PGF to the right. In digitoninpermeabilized astrocytes, phloretin (100 μ M ) inhibited the stimulation induced by PGF (1 μ M ) plus GTPγS (50 μ M ) without affecting that induced by GTPγS alone. PGF at 1 μ M transiently increased astrocytic intracellular Ca2+ concentration in 39% of the cells tested. The response was completely blocked by 100 μ M phloretin and the calcium response recovered again after washing out phloretin. These results suggest that phloretin is an antagonist of PGF receptor linked to phospholipase C in astrocytes.
Keywords:Prostaglandin F receptor    Phloretin    Phosphoinositide hydrolysis    Calcium mobilization    Astrocytes
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