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

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

doi:10.1074/jbc.m400356200

Ming-Wei Lin, Su-Rong Yang + Show 2 more

Open Access

https://doi.org/10.1074/jbc.m400356200

Copy DOI

Abstract

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-kappaB. Its effects on ion currents have been investigated in pituitary GH(3) cells. This compound increased Ca(2+)-activated K(+) current (I(K(Ca))) in a concentration-dependent manner with an EC(50) value of 14 +/- 2 microm. However, the magnitude of CAPE-induced stimulation of I(K(Ca)) was attenuated in GH(3) cells preincubated with 2,2'-azo-bis-(2-amidinopropane) hydrochloride (100 microm) or t-butyl hydroperoxide (1 mm). CAPE (50 microm) slightly suppressed voltage-dependent L-type Ca(2+) current. In inside-out configuration, CAPE (20 microm) applied to the intracellular face of the detached patch enhanced the activity of large conductance Ca(2+)-activated K(+) (BK(Ca)) channels with no modification in single-channel conductance. After BK(Ca) channel activity was increased by CAPE (20 microm), subsequent application of nordihydroguaiaretic acid (20 microm) did not further increase the channel activity. CAPE-stimulated channel activity was dependent on membrane potential. CAPE could also increase Ca(2+) 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-kappaB.

Highlights

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
Effect of CAPE on Ca2ϩ-activated Kϩ Current (IK(Ca)) in GH3 Cells—In the first series of experiments, the whole cell configuration of the patch-clamp technique was used to investigate the effect of CAPE on ion currents in these cells
This study shows that CAPE (a) increases the amplitude of IK(Ca) in a concentration-dependent manner in pituitary GH3 cells, (b) enhances the activity of BKCa channel in a voltagedependent manner, and (c) reduces the repetitive firing of action potentials

Summary

Introduction

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. Large conductance Ca2ϩ-activated Kϩ (BKCa) channels play important roles in controlling the excitability of nerve, muscle, and other cells by stabilizing cell membrane at negative potentials [11]. Pituitary GH3 cells have been demonstrated to exhibit the activity of these channels [13] Riluzole and ciglitazone, both of which were reported to prevent neuronal injuries, could enhance the activity of BKCa channels functionally expressed in these cells [14, 15]. The objective of this study was to (a) address the question of whether CAPE could affect Ca2ϩ-activated Kϩ currents (IK(Ca)) in GH3 cells; (b) determine the effects of this compound on the activity of BKCa channels; and (c) examine whether it can influence the membrane potential. The CAPE-induced increase in BKCa channel activity may account, at least in part, for its effects on cellular functions in neurons or neuroendocrine cells

Objectives

Methods

Results

Conclusion