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J. Biol. Chem., Vol. 279, Issue 26, 26885-26892, June 25, 2004

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Stimulatory Actions of Caffeic Acid Phenethyl Ester, a Known Inhibitor of NF-B Activation, on Ca²+-activated K⁺ Current in Pituitary GH₃ Cells^*

Ming-Wei Lin, Su-Rong Yang, Mei-Han Huang, and Sheng-Nan Wu

From the Institute of Basic Medical Sciences, National Cheng-Kung University Medical College, Tainan 701, Taiwan

Caffeic acid phenethyl ester (CAPE), a phenolic antioxidant derived from the propolis of honeybee hives, is known to be an inhibitor of activation of nuclear transcript factor NF-B. Its effects on ion currents have been investigated in pituitary GH₃ cells. This compound increased Ca²⁺-activated K⁺ current (I_K(Ca)) in a concentration-dependent manner with an EC₅₀ value of 14 ± 2 µM. However, the magnitude of CAPE-induced stimulation of I_K(Ca) was attenuated in GH₃ cells preincubated with 2,2'-azo-bis-(2-amidinopropane) hydrochloride (100 µM) or t-butyl hydroperoxide (1 mM). CAPE (50 µM) slightly suppressed voltage-dependent L-type Ca²⁺ current. In inside-out configuration, CAPE (20 µM) applied to the intracellular face of the detached patch enhanced the activity of large conductance Ca²⁺-activated K⁺ (BK_Ca) channels with no modification in single-channel conductance. After BK_Ca channel activity was increased by CAPE (20 µM), subsequent application of nordihydroguaiaretic acid (20 µM) did not further increase the channel activity. CAPE-stimulated channel activity was dependent on membrane potential. CAPE could also increase Ca²⁺ sensitivity of BK_Ca channels in these cells. Its increase in the open probability could primarily involve a decrease in the mean closed time. In current-clamp conditions, CAPE hyperpolarized the membrane potential and reduced the firing of action potentials. The stimulatory effects on these channels may partly contribute to the underlying mechanisms through which this compound influences the functional activities of neurons or neuroendocrine cells. Caution has to be used in attributing its response in the activation of NF-B.

Received for publication, January 13, 2004 , and in revised form, March 22, 2004.

^* This work was supported by National Science Council Grants NSC-91-2320B-006-106 and NSC-92-2320B-006-041. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

To whom correspondence should be addressed: Institute of Basic Medical Sciences, National Cheng-Kung University Medical College, No. 1, University Road, Tainan 701, Taiwan. Tel.: 886-6-2353535-5334; Fax: 886-6-2353660; e-mail: snwu{at}mail.ncku.edu.tw.

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