We attempted to characterize the general features of arachidonate metabolism in cultured mouse keratinocytes. The cells labeled with [3H]arachidonate were stimulated by 12-O-tetradecanoylphorbol-13-acetate (TPA), ionophore A23187, and fetal bovine serum (FBS). Common to the three substances, phosphatidylinositol, phosphatidylethanolamine, and phosphatidylcholine almost equally served as sources of arachidonate liberated by the action of phospholipase A2. The stimulation of phospholipase A2 action was observed in the order of A23187 greater than FBS greater than TPA. When stimulated by TPA or A23187, the radioactivity released into the extracellular medium was mostly found in prostaglandin (PG) E2. Formation of other PGs and hydroxyeicosatetraenoate (HETE) was extremely limited. In the case of stimulation by FBS, however, the released radioactivity was mainly associated with non-converted arachidonate. FBS also inhibited the TPA- and A23187-induced conversion of arachidonate to PGE2. Phospholipid degradation induced by the three stimulators was similarly dependent on extracellular Ca2+. The stimulation by FBS and A23187 was suppressed by calmodulin antagonists, though the effect of A23187 was much more sensitive to the antagonists when compared to that of FBS. We observed more than additive effects of the three stimulators when tested together.
Olfactory receptor cells are widely thought to regenerate after degeneration and also thought to show turnover in normal circumstances in animal olfactory epithelium. The identity of the factor that controls proliferation and differentiation of olfactory receptor cells is a very important problem that has yet to be resolved. In this study, the mitogenic effects of epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) on olfactory receptor cells in guinea pig olfactory epithelium was examined. The intraperitoneal injection of 1,000 ng bFGF/day for 14 days increased the cells in proliferation detected by immunostaining with proliferating cell nuclear antigen (PCNA), while neither EGF nor low-dose bFGF had any effect. These results support the idea that an adequate dose of bFGF plays an important role in the neurogenesis in the olfactory epithelium. Further study is needed to clarify the efficacy of bFGF in the damaged olfactory epithelium, but bFGF may provide a therapeutic option for olfactory disturbances caused by complete or partial loss of olfactory receptor cells.
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