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Properties of BK_Ca Channels in Oral Keratinocytes

¹ Institute of Oral Medicine, ² Institute of Molecular Medicine, ³ Institute of Basic Medical Sciences, and ⁴ Department of Physiology, National Cheng Kung University Medical College, No. 1, University Road, Tainan 701, Taiwan;

^* corresponding author, snwu{at}mail.ncku.edu.tw

	ABSTRACT

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Keratinocytes are important for epithelial antimicrobial barrier function. The activity of ion channels can affect the proliferation of keratinocytes. Little is known about Ca²⁺-activated K⁺ currents in these cells. Ion currents in normal human oral keratinocytes were characterized with a patch-clamp technique. In whole-cell configuration, depolarizing pulses evoked K⁺ outward currents (I_K) in oral keratinocytes. Iberiotoxin (200 nM) and paxilline (1 µM) suppressed I_K; however, neither apamin (200 nM) nor 5-hydroxydecanoate (30 µM) had any effects on it. Caffeic acid phenethyl ester, a compound of honeybee propolis, increased I_K with an EC₅₀ value of 12.8 ± 1.2 µM. In inside-out patches, a BK_Ca channel was observed in keratinocytes, but not in oral squamous carcinoma (OCE-M1) cells. Caffeic acid phenethyl ester or cinnamyl-3,4-dihydroxy--cyanocinnamate applied to the intracellular surface of a detached patch increased BK_Ca-channel activity. The results demonstrate that the properties of BK_Ca channels in normal human oral keratinocytes are similar to those described in other types of cells. Caffeic acid derivatives can also stimulate BK_Ca-channel activity directly.

KEY WORDS: K⁺ current • large-conductance Ca²⁺-activated K⁺ channel • caffeic acid esters • normal human oral keratinocyte

	INTRODUCTION

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Keratinocytes are critical to the epithelial antimicrobial barrier between an organism and the outside hostile environment (Koreck et al., 2003; Chung and Dale, 2004). Many ion currents have been identified in keratinocytes (Mauro et al., 1990; Wohlrab et al., 2000; Nguyen and Markwardt, 2002; Guitard et al., 2004). Previous reports demonstrated that the intermediate-conductance Ca²⁺-activated K⁺ channel was expressed in keratinocytes (Mauro et al., 1997; Koegel and Alzheimer, 2001; Koegel et al., 2003). The large-conductance K⁺ and Cl^– channels were also described in HaCaT cells (Wohlrab et al., 2000; Nguyen and Markwardt, 2002). More importantly, ion fluxes through ion channels influence the proliferation and apoptosis of many cell types, including keratinocytes (Dubois and Rouzaire-Dubois, 1993; Mauro et al., 1993; Liu et al., 1998; Huang et al., 2002; Liu et al., 2003). Ca²⁺-induced differentiation of keratinocytes was associated with the K⁺ channel activity (Mauro et al., 1997).

The large-conductance Ca²⁺-activated K⁺ (BK_Ca) channel is selective for K⁺ ions. These channels, which are products of a nearly ubiquitous, alternatively spliced gene (Slo) (Butler et al., 1993), are distinguished from other K⁺ channels in that their activation is under dual control, i.e., activated by membrane depolarization or by increased intracellular Ca²⁺. They are blocked by various indole diterpenes (e.g., paxilline) (Li et al., 2000; Liu et al., 2003; Wu, 2003). A recent study demonstrated that BK_Ca-channel activity was related to microbicidal function of neutrophils (Ahluwalia et al., 2004). However, it remains unclear whether these channels are present in keratinocytes.

Caffeic acid phenethyl ester, one of the major components of honeybee propolis, is an inhibitor of activation of nuclear transcript factor NF-B (Natarajan et al., 1996). It stimulates proliferation of wound epidermis keratinocytes (Brudzynski and Carlone, 2004). This compound inhibits the activity of cyclooxygenase-2 in oral epithelial cells (Michaluart et al., 1999). Caffeic acid phenethyl ester and its analogues might have preferential cytotoxicity on oral cancer cells (Lee et al., 2000). In addition, caffeic acid derivatives enhanced the activity of background K⁺ channels in adrenal fasciculate cells (Danthi et al., 2004). However, it remains largely unknown whether these compounds have any effects on ion currents in keratinocytes.

Therefore, we sought to: (1) identify whether Ca²⁺-activated K⁺ currents are present in primary cultures of normal human oral keratinocytes; (2) characterize the properties of BK_Ca channels; and (3) investigate whether caffeic acid phenethyl ester and other related compounds interact with the BK_Ca channel.

	MATERIALS & METHODS

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Cell Preparations
Primary cultures of normal human oral keratinocytes were prepared from keratinizing oral epithelial tissue collected from gingival tissue during third molar extraction. Cells were cultured in keratinocyte serum-free medium (Life Technologies, Grand Island, NY, USA), with low Ca²⁺ (0.1 mM) on flasks coated with rat-tail collagen (Yang et al., 2003). Cells were grown in 50-mL plastic culture flasks in a humidified environment of 5% CO₂/95% air at 37°C. The OEC-M1 cell line, derived from the gingival squamous cell carcinoma of a Chinese patient (Meng et al., 1998), was maintained in 5-mL RPMI-1640 culture media (Life Technologies) supplemented with 10% FBS, 2 mM L-glutamine, and 25 mM HEPES. The patients provided informed consent for this study, and the study protocol was approved by a local ethical committee.

Electrophysiological Measurements
Cells were bathed at room temperature in normal Tyrode’s solution. Patch pipettes were made with the use of a PP-830 electrode puller (Narishige, Tokyo, Japan). Their resistance ranged between 3 and 5 M. Ion currents passing through the whole-cell (whole-cell configuration) or a detached patch (inside-out configuration) were measured by the patch-clamp technique, with the use of an RK-400 patch-clamp amplifier (Bio-Logic, Claix, France) (Wu et al., 2003). The signals were displayed on an HM-507 oscilloscope (Hameg, East Meadow, NY, USA). The data were stored in a personal computer (Lemel, Taipei, Taiwan), which was controlled by pCLAMP 9.0 (Axon, Union City, CA, USA). Whole-cell currents were recorded without leak compensation. Cell capacitance in normal human oral keratinocytes ranged between 21 and 34 pF (n = 12). The expression density of the BK_Ca channel was calculated to 823 ± 34 per cell (n = 13).

To calculate the percentage increase of caffeic acid phenethyl ester on I_K (K⁺ outward current), we depolarized each cell from –40 to +50 mV, and compared the current amplitudes during the exposure to caffeic acid phenethyl ester. The amplitude of I_K in the presence of 300 µM caffeic acid phenethyl ester was taken as 100%. The concentration required to stimulate 50% of current amplitude was determined by means of a Hill function. That is, percentage increase = (E_max [C]^nh)/(EC₅₀^nh+[C]^nh), where [C] is the concentration of caffeic acid phenethyl ester; EC₅₀ and n_h are the concentrations required for a 50% stimulation and the Hill coefficient, respectively; and E_max is the maximal increase in current amplitude caused by caffeic acid phenethyl ester.

The relationships between membrane potentials and the relative open probability of BK_Ca channels before and after application of caffeic acid phenethyl ester or cinnamyl-3,4-dihydroxy--cyanocinnamate were fitted with a Boltzmann function of the form: relative open probability = n_P/{1+exp[-(V-V_1/2)/k]}, where n_P = the maximal open probability, V = the membrane potential in mV, V_1/2 = the voltage at which there is half-maximal activation, and k = the slope factor of the activation curve. The averaged results are presented as the means ± SEM. The paired Student’s t test and one-way ANOVA were used for the statistical analyses. Differences between values were considered significant when P < 0.05 or P < 0.01.

Drugs and Solutions
Anandamide and caffeic acid phenethyl ester were obtained from Cayman (Ann Arbor, MI, USA), cinnamyl-3,4-dihydroxy--cyanocinnamate, caffeic acid, 5-hydroxydecanoate sodium, and paxilline from Biomol (Plymouth Meeting, PA, USA), and iberiotoxin and apamin were obtained from Alomone Labs (Jerusalem, Israel). Tetraethylammonium chloride was purchased from Sigma (St. Louis, MO, USA), ionomycin from Molecular Probes (Eugene, OR, USA), and nordihydroguaiaretic acid from Sigma/RBI (Natick, MA, USA). Squamocin was a gift from Dr. Yang-Chang Wu (Kaohsiung Medical University, Kaohsiung City, Taiwan).

The composition of normal Tyrode’s solution was 136.5 mM NaCl, 5.4 mM KCl, 1.8 mM CaCl₂, 0.53 mM MgCl₂, 5.5 mM glucose, and 5.5 mM HEPES-NaOH buffer, pH 7.4. To record K⁺ currents, we back-filled the recording pipette with a solution consisting of 140 mM KCl, 1 mM MgCl₂, 3 mM Na₂ ATP, 0.1 mM Na₂GTP, 0.1 mM EGTA, and 5 mM HEPES-KOH buffer, pH 7.2. For single-channel recordings, the high-K⁺ bathing solution contained 145 mM KCl, 0.53 MgCl₂, and 5 mM HEPES-KOH buffer, pH 7.4, and the pipette was back-filled with a solution containing 145 mM KCl, 2 mM MgCl₂, and 5 mM HEPES-KOH buffer, pH 7.2.

	RESULTS

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Properties of I_K in Normal Human Oral Keratinocytes
Initially, whole-cell experiments were used to investigate the properties of I_K in these cells. Cells were bathed in normal Tyrode’s solution containing 1.8 mM CaCl₂. When voltage pulses ranging from –30 to +70 mV in 20-mV increments were applied with a duration of 300 msec at a rate of 0.1 Hz, a family of outward currents was evoked (Fig. 1A). When extracellular Ca²⁺ was removed, I_K was reduced throughout all voltage steps. The current-voltage relationships of I_K in the absence and the presence of extracellular Ca²⁺ are illustrated in Fig. 1B. The increase of intracellular EGTA from 0.1 to 10 mM also abolished I_K. Unlike that in HaCaT keratinocytes (Nguyen and Markwardt, 2002), the amplitude of I_K depends on intracellular Ca²⁺.

View larger version (28K): [in this window] [in a new window]   Figure 1. Effects of removal of extracellular Ca2+ and various related compounds on IK in normal human oral keratinocytes. Cells were bathed in normal Tyrode’s solution containing 1.8 mM CaCl2. (A) Superimposed current tracings obtained in the absence and presence of external CaCl2. The cell was held at –40 mV, and the depolarizing pulses from –30 to +70 mV were delivered in 20-mV increments. The pipette solution contained 0.1 mM EGTA. The superimposed current traces shown in Aa are control, and those in Ab were obtained 2 min after cells were exposed to Ca2+-free solution containing 1 mM EGTA. (B) The current-voltage relations of outward currents in the presence and absence of extracellular Ca2+ concentration. • : 1.8 mM Ca2+; : Ca2+-free. Mean ± SEM (n = 6–8). (C) Bar graph showing the effects of various blockers of K+ channels on the relative amplitude of IK in normal human oral keratinocytes. In these experiments, cells were bathed in normal Tyrode’s solution containing 1.8 mM CaCl2, and the depolarizing pulses from –40 to +50 mV were applied. Current amplitude in the control was considered to be 1.0, and the relative amplitudes in the presence of each agent were compared. Pax, paxilline (1 µM); Iber, iberitoxin (200 nM); TEA, tetraethylammonium chloride (10 mM); Apa, apamin (200 nM); 5HD, 5-hydroxydecanoate sodium (10 µM); and Anan, anandamide (10 µM). The number of cells from which the data were taken is shown above the bars. Mean ± SEM. *Significantly different from the control group.

Stimulatory Effect of Caffeic Acid Phenethyl Ester on I_K
Caffeic acid phenethyl ester, a natural compound of honeybee propolis, could increase proliferation of wound epidermis keratinocytes (Brudzynski and Carlone, 2004). Caffeic acid phenethyl ester and cinnamyl-3,4-dihydroxy--cyanocinnamate were shown to enhance the activity of background K⁺ channels in adrenal fasciculate cells (Danthi et al., 2004). Cinnamyl-3,4-dihydroxy--cyanocinnamate is a structurally related compound of caffeic acid phenethyl ester. The effects of these compounds on I_K were thus investigated in normal human oral keratinocytes. Interestingly, they stimulated I_K. When the ramp pulses from –80 to +100 mV were applied, caffeic acid phenethyl ester triggered an increase in I_K (Fig. 2A). At +80 mV, caffeic acid phenethyl ester (10 µM) increased I_K from 512 ± 24 to 1785 ± 89 pA (n = 7). A subsequent application of paxilline (1 µM) reduced I_K to 784 ± 32 pA (n = 6). The relationship between the concentration of this compound and the percentage stimulation of I_K was constructed (Fig. 2B). The half-maximal concentration required for its stimulation of I_K was 12.8 ± 1.2 µM (n = 6).

View larger version (16K): [in this window] [in a new window]   Figure 2. Effect of caffeic acid phenethyl ester on IK in normal human oral keratinocytes. (A) Original current tracings obtained when the cell was held at –40 mV and the ramp pulses from –80 to +100 mV with a duration of 1 sec were applied. "a" is the control, "b" was recorded in the presence of caffeic acid phenethyl ester (10 µM), and "c" was obtained after the application of caffeic acid phenethyl ester plus paxilline (1 µM). (B) Concentration-dependent stimulation of caffeic acid phenethyl ester on IK in normal human oral keratinocytes. Each cell was depolarized from –40 to +50 mV. Current amplitude in the presence of 300 µM caffeic acid phenethyl ester was considered to be 100%. The smooth line is the fit of the data with a Hill function as described in MATERIALS & METHODS. The values for EC50, maximally stimulated percentage of IK, and the Hill coefficient were 12.8 ± 1.2 µM, 99 ± 1%, and 1.2 ± 0.1 (n = 5). (C) Bar graph showing the effects of caffeic acid phenethyl ester, cinnamyl-3,4-dihydroxy--cyanocinnamate, nordihydroguaiaretic acid, caffeic acid phenethyl ester plus paxilline, and caffeic acid phenethyl ester plus anandamide on the amplitude of IK. Each cell was depolarized from –40 to +50 mV. Current amplitudes were measured at the end of depolarizing pulses. The amplitude in the control was considered to be 1.0, and the relative amplitudes during exposure to each agent were compared. Mean ± SEM (n = 5–7). CAPE, caffeic acid phenethyl ester (10 µM); CDC, cinnamyl-3,4-dihydroxy--cyanocinnamate (10 µM); NDGA, nordihydroguaiaretic acid (10 µM); Pax, paxilline (1 µM); and Anan, anandamide (10 µM). *Significantly different from the control group. **Significantly different from the group with caffeic acid phenethyl ester alone.

Properties of BK_Ca Channels in Oral Keratinocytes
Single BK_Ca-channel currents were further characterized from cell-attached and inside-out patches. The K⁺ concentration in the bathing and pipette solutions was 145 mM. The increased channel activity was observed in cell-attached patches during the exposure to ionomycin (10 µM) or squamocin (10 µM) (Fig. 3), both of which are Ca²⁺ ionophores (Wu et al., 2003). A subsequent application of paxilline (1 µM) reduced squamocin-stimulated channel activity. Moreover, channel activity persisted when external Cl^– was replaced by aspartate. However, in an oral carcinoma cell line (OCE-M1), we did not observe BK_Ca-channel activity in cell-attached or inside-out patches from 15 different cells.

View larger version (20K): [in this window] [in a new window]   Figure 3. The activity of BKCa channels in cell-attached patches from normal human oral keratinocytes. Cells were bathed in 145 mM K+ solution containing 1.8 mM CaCl2, and the holding potential was set at +60 mV. (A) Original current tracings obtained in the absence and presence of ionomycin, squamocin, and squamocin plus paxilline. "a" is the control, "b" and "c" were obtained in the presence of either ionomycin (10 µM) or squamocin (10 µM), respectively, and "d" was recorded after application of squamocin (10 µM) plus paxilline (1 µM). (B) Bar graph showing the effects of ionomycin (10 µM), squamocin (10 µM), and squamocin (10 µM) plus paxilline (1 µM) on BKCa-channel activity. Mean ± SEM (n = 6–8). *Significantly different from control group. **Significantly different from squamocin-alone group.

View larger version (18K): [in this window] [in a new window]   Figure 4. Ca2+- and voltage-dependence of the caffeic acid phenethyl ester-induced increase in BKCa-channel activity in inside-out patches of normal human oral keratinocytes. (A) Original current tracings showing the effect of internal Ca2+ on the probability of channel openings. The potential was held at +60 mV. "a", "b", and "c" were obtained after the application of 0.1, 1, and 10 µM Ca2+, respectively. (B) Bar graph showing the stimulation of BKCa channels by caffeic acid phenethyl ester at different concentrations of internal Ca2+. The different concentrations of Ca2+ in the bath before and during exposure to 10 µM caffeic acid phenethyl ester were applied. Each patch was held at +60 mV. Mean ± SEM (n = 4–6). (C) Voltage dependence of the caffeic acid phenethyl ester- and cinnamyl-3,4-dihydroxy--cyanocinnamate-induced increase in BKCa-channel activity of normal human oral keratinocytes. Inside-out patch recordings were performed, and bath medium contained 0.1 µM Ca2+. Caffeic acid phenethyl ester or cinnamyl-3,4-dihydroxy--cyanocinnamate was applied to the intracellular surface of the detached patch. The open probability at +100 mV in the control was taken as 1.0. The activation curves of BKCa channels in the absence (•) and presence of caffeic acid phenethyl ester (10 µM; ) or cinnamyl-3,4-dihydroxy--cyanocinnamate (10 µM; ) were obtained. Mean ± SEM (n = 4–7).

Effect of Caffeic Acid Phenethyl Ester or Cinnamyl-3,4-dihydroxy--cyanocinnamate on the Activation Curve of BK_Ca Channels

	DISCUSSION

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In this report, we described a BK_Ca channel in human oral keratinocytes. The single-channel conductance of BK_Ca channels was 152 ± 8 pS (n = 8), a value that is similar to that of BK_Ca channels in other cell types (Sheu and Wu, 2003; Wu et al., 2003), but is greater than that of small- or intermediate-conductance Ca²⁺-activated K⁺ channels (Mauro et al., 1997; Nguyen and Markwardt, 2002; Koegel et al., 2003), or of the tandem-pore K⁺ channel (Maingret et al., 2001). In addition, unlike that measured from HaKaT keratinocytes (Nguyen and Markwardt, 2002), the large-conductance K⁺ channel presented here is responsive to membrane depolarization and/or increased intracellular Ca²⁺. The increase in extracellular Ca²⁺ may promote Ca²⁺ influx, thus leading to the elevation of intracellular Ca²⁺. However, whether different patterns of Ca²⁺-activated K⁺ channels in keratinocytes affect cell growth and differentiation remains to be clarified. Indeed, no BK_Ca-channel activity was found in an oral carcinoma cell line (OEC-M1).

Keratinocytes are important for epithelial antimicrobial barrier function (Koreck et al., 2003; Chung and Dale, 2004). BK_Ca-channel activity contributes to K⁺ efflux across cell membranes because of large conductance. Previous studies have demonstrated the ability of keratinocytes to engulf large oligolamellar liposomes (Korting et al., 1993). The BK_Ca channel has an impact on the functional activity of keratinocytes.

Notably, caffeic acid phenethyl ester, cinnamyl-3,4-dihydroxy--cyanocinnamate, and nordihydroguaiaretic acid stimulate I_K in normal human oral keratinocytes, although caffeic acid phenethyl ester and nordihydroguaiaretic acid suppress the activity of cyclooxygenase or inhibit NF-B activation (Natarajan et al., 1996; Michaluart et al., 1999; Gonzales and Bowden, 2002). Chemical structures of these compounds share the juxtaposition of two aromatic rings that seem to be essential for their ability to activate BK_Ca channels (Wu, 2003). Caffeic acid phenethyl ester (10 µM) increased open probability; however, a subsequent application of cinnamyl-3,4-dihydroxy--cyanocinnamate (10 µM) did not increase channel activity further (data not shown). Caffeic acid phenethyl ester and cinnamyl-3,4-dihydroxy--cyanocinnamate were reported to stimulate background K⁺ channels (Danthi et al., 2004), whereas nordihydroguaiaretic acid activates BK_Ca channels (Wu, 2003). However, unlike caffeic acid, caffeic acid phenethyl ester or cinnamyl-3,4-dihydroxy--cyanocinnamate enhanced BK_Ca-channel activity in oral keratinocytes. These compounds interact with the internal leaflet of the channel. The stimulation of BK_Ca channels caused by these compounds also depended on intracellular Ca²⁺ and/or membrane polarization. Their effects on ion channels are unrelated to inhibition of NF-B or cyclooxygenase.

Ca²⁺-activated K⁺ channels play a role in the control of cell growth (Huang et al., 2002; Liu et al., 2003). Increased extracellular Ca²⁺ serves as a trigger for keratinocyte differentiation (Guitard et al., 2004). Ca²⁺-induced differentiation in keratinocytes was associated with K⁺ channel activity (Mauro et al., 1997). Caffeic acid phenethyl ester enhances the proliferation of wound epidermis keratinocytes (Brudzynski and Carlone, 2004). The lost channel activity in cancer cells may prevent their further differentiation and enhance their proliferation activity.

	ACKNOWLEDGMENTS

 
This study has been funded by grants from the National Science Council (NSC-91-2320B-006-106, NSC-92-2320B-006-041, and NSC-92-2314-B006-088), Taiwan.

Received May 14, 2004; Last revision February 2, 2005; Accepted February 4, 2005

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS & METHODS RESULTS DISCUSSION REFERENCES

 
Ahluwalia J, Tinker A, Clapp LH, Duchen MR, Abramov AY, Pope S, et al. (2004), The large-conductance Ca²⁺-activated K⁺ channel is essential for innate immunity. Nature 427:853–858.[Medline]

Brudzynski K, Carlone R (2004). Stage-dependent modulation of limb regeneration by caffeic acid phenethyl ester (CAPE)-immunocytochemical evidence of a CAPE-evoked delay in mesenchyme formation and limb regeneration. J Exp Zoolog A Comp Exp Biol 301:389–400.

Butler A, Tsunoda S, McCobb DP, Wei A, Salkoff L (1993). mSlo, a complex mouse gene encoding ‘maxi’ calcium-activated potassium channels. Science 261:221–224.[Abstract/Free Full Text]

Chung WO, Dale BA (2004). Innate immune response of oral and foreskin keratinocytes: utilization of different signaling pathways by various bacterial species. Infect Immun 72:352–358.[Abstract/Free Full Text]

Danthi S, Enyeart JA, Enyeart JJ (2004). Caffeic acid esters activate TREK-1 potassium channels and inhibit depolarization-dependent secretion. Mol Pharmacol 65:599–610.[Abstract/Free Full Text]

Dubois JM, Rouzaire-Dubois B (1993). Role of potassium channels in mitogenesis. Prog Biophys Mol Biol 59:1–21.[ISI][Medline]

Gonzales M, Bowden GT (2002). Nordihydroguaiaretic acid-mediated inhibition of ultraviolet B-induced activator protein-1 activation in human keratinocytes. Mol Carcinogen 34:102–111.[ISI][Medline]

Guitard M, Leyvraz C, Hummler E (2004). A nonconventional look at ionic fluxes in the skin: lessons from genetically modified mice. New Physiol Sci 19:75–79.[Abstract/Free Full Text]

Huang MH, Wu SN, Chen CP, Shen AY (2002). Inhibition of Ca²⁺-activated and voltage-dependent K⁺ currents by 2-mercaptophenyl-1,4-naphthoquinone in pituitary GH₃ cells: contribution to its antiproliferative effect. Life Sci 70:1185–1203.[ISI][Medline]

Koegel H, Alzheimer C (2001). Expression and biological significance of Ca²⁺-activated ion channels in human keratinocytes. FASEB J 15:145–154.[Abstract/Free Full Text]

Koegel H, Kaesler S, Burgstahler R, Werner S, Alzheimer C (2003). Unexpected down-regulation of the hIK1 Ca²⁺-activated channel by its opener 1-ethyl-2-benzimidazolinone in HaCaT keratinocytes. Inverse effects on cell growth and proliferation. J Biol Chem 278:3323–3330.[Abstract/Free Full Text]

Koreck A, Pivarcsi A, Dobozy A, Kemeny L (2003). The role of innate immunity in the pathogenesis of acne. Dermatology 206:96–105.[ISI][Medline]

Korting HC, Schmid MH, Hartinger A, Maierhofer G, Stolz W, Braun-Falco O (1993). Evidence for the phagocytosis of intact oligolamellar liposomes by human keratinocytes in vitro and consecutive intracellular disintegration. J Microencapsul 10:223–228.[ISI][Medline]

Lee YJ, Liao PH, Chen WK, Yang CY (2000). Preferential cytotoxicity of caffeic acid phenethyl ester analogues on oral cancer cells. Cancer Lett 153:51–56.[ISI][Medline]

Li HF, Chen SA, Wu SN (2000). Evidence for the stimulatory effect of resveratrol on Ca²⁺-activated K⁺ current in vascular endothelial cells. Cardiovasc Res 45:1035–1045.[Abstract/Free Full Text]

Liu SI, Chi CW, Lui WY, Mok KT, Wu CW, Wu SN (1998). Correlation of hepatocyte growth factor-induced proliferation and calcium-activated potassium current in human gastric cancer cells. Biochim Biophys Acta 1368:256–266.[Medline]

Liu YC, Lo YC, Huang CW, Wu SN (2003). Inhibitory action of ICI-182,780, an estrogen receptor antagonist, on BK_Ca channel activity in cultured endothelial cells of human coronary artery. Biochem Pharmacol 66:2053–2063.[ISI][Medline]

Maingret F, Patel AJ, Lazdunski M, Honoré E (2001). The endocannabinoid anandamide is a direct and selective blocker of the background K⁺ channel TASK-1. EMBO J 20:47–54.[ISI][Medline]

Mauro TM, Pappone PA, Isseroff RR (1990). Extracellular calcium affects the membrane currents of cultured human keratinocytes. J Cell Physiol 143:13–20.[ISI][Medline]

Mauro TM, Isseroff RR, Lasarow R, Pappone PA (1993). Ion channels are linked to differentiation in keratinocytes. J Membr Biol 132:201–209; erratum, J Membr Biol 1993 134:168.[ISI][Medline]

Mauro T, Dixon DB, Komuves L, Hanley K, Pappone PA (1997). Keratinocyte K⁺ channels mediate Ca²⁺-induced differentiation. J Invest Dermatol 108:864–870.[ISI][Medline]

Meng CL, Yang CY, Shen KL, Wong PY, Lee HK (1998). Inhibition of the synthesis of eicosanoid-like substances in a human oral cancer cell line by interferon-gamma and eicosapentaenoic acid. Arch Oral Biol 43:979–986.[ISI][Medline]

Michaluart P, Masferrer JL, Carothers AM, Subbaramaiah K, Zweifel BS, Koboldt C, et al. (1999). Inhibitory effects of caffeic acid phenethyl ester on the activity and expression of cyclooxygenase-2 in human oral epithelial cells and in a rat model of inflammation. Cancer Res 59:2347–2352.[Abstract/Free Full Text]

Natarajan K, Singh S, Burke TR Jr, Grunberger D, Aggarwal BB (1996). Caffeic acid phenethyl ester is a potent and specific inhibitor of activation of nuclear transcription factor NF-B. Proc Natl Acad Sci USA 93:9090–9095.[Abstract/Free Full Text]

Nguyen VH, Markwardt F (2002). A large conductance [Ca(2+)](-)-independent K+ channel expressed in HaCaT keratinocytes. Exp Dermatol 1:319–326.

Sheu SJ, Wu SN (2003). Mechanism of inhibitory actions of oxidizing agents on calcium-activated potassium current in cultured pigment epithelial cells of the human retina. Invest Ophthalmol Vis Sci 44:1237–1244.[Abstract/Free Full Text]

Wohlrab D, Wohlrab J, Markwardt F (2000). Electrophysiological characterization of human keratinocytes using the patch-clamp technique. Exp Dermatol 9:219–223.[ISI][Medline]

Wu SN (2003). Large-conductance Ca²⁺-activated K⁺ channels: physiological role and pharmacology. Curr Med Chem 10:649–661.[ISI][Medline]

Wu SN, Chiang HT, Chang FR, Liaw CC, Wu YC (2003). Stimulatory effects of squamocin, an Annoaceous acetogenin, on Ca(2+)-activated K+ current in cultured smooth muscle cells of human coronary artery. Chem Res Toxicol 16:15–22.[ISI][Medline]

Yang SC, Lin SC, Chiang WF, Yen CY, Lin CH, Liu SY (2003). Areca nut extract treatment elicits the fibroblastoid morphological changes, actin re-organization and signaling activation in oral kertinocytes. J Oral Pathol Med 32:600–605.[ISI][Medline]

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