Ikuko Yokoyama

Publications (2)6.25 Total impact

• Article: T-588, a cognitive enhancer, stimulates in vivo phosphorylation of extracellular signal-regulated kinases in the hippocampus.

  Ikuko Yokoyama, Yoshiyuki Sakai, Yuki Hatayama, Shingo Tsuji, Yutaka Koyama, Akemichi Baba, Toshio Matsuda
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  ABSTRACT: Administration of (1R)-1-benzo[b]thiophen-5-yl-2-[2-(diethylamino)ethoxy]ethan-1-ol hydrochloride (T-588), a cognitive enhancer, like the acetylcholine esterase inhibitors physostigmine and tacrine, stimulated phosphorylation of extracellular signal-regulated kinases (ERK) in the mouse hippocampus. The effect of T-588 on ERK phosphorylation was persistent from 2 to 6 h after injection. Immunohistochemical study showed that T-588 stimulated neuronal ERK phosphorylation in rat hippocampal CA1 pyramidal subfield. These findings suggest that systemic T-588 stimulates the ERK kinase pathway in the hippocampal neurons.
  Cognitive Brain Research 08/2003; 17(2):522-5. · 3.77 Impact Factor
• Article: KB-R7943 Inhibits Store-Operated Ca2+ Entry in Cultured Neurons and Astrocytes

  Naohisa Arakawa, Masaki Sakaue, Ikuko Yokoyama, Hitoshi Hashimoto, Yutaka Koyama, Akemichi Baba, Toshio Matsuda
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  ABSTRACT: We have studied cyclopiazonic acid (CPA)-sensitive store-operated Ca2+ entry (SOCE) in cultured neurons and astrocytes and examined the effect of 2-[2-[4-(4-nitrobenzyloxy)phenyl]]isothiourea (KB-R7943), which is often used as a selective inhibitor of the Na+–Ca2+ exchanger (NCX), on the SOCE. CPA increased transiently intracellular Ca2+ concentration ([Ca2+]i) followed by a sustained increase in [Ca2+]i in neurons and astrocytes. The sustained increase in [Ca2+]i depended on the presence of extracellular Ca2+ and inhibited by SOCE inhibitors, but not by a Ca2+ channel inhibitor. CPA also caused quenching of fura-2 fluorescence when the cells were incubated in Mn2+-containing medium. KB-R7943 at 10 μM inhibited significantly CPA-induced sustained increase in [Ca2+]i in neurons and astrocytes. KB-R7943 also inhibited CPA-induced quenching of fura-2 fluorescence in the presence of extracellular Mn2+. These results indicate that cultured neurons and astrocytes possess SOCE and that KB-R7943 inhibits not only NCX but also SOCE.
  Biochemical and Biophysical Research Communications 279(2):354-357. · 2.48 Impact Factor