The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
Lane A Baker - One of the best experts on this subject based on the ideXlab platform.
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effects of pipette modulatIon and imaging distances on Ion Currents measured with scanning Ion conductance microscopy sicm
Analyst, 2011Co-Authors: Chiaochen Chen, Lane A BakerAbstract:Local conductance variatIons can be estimated by measuring Ion current magnitudes with scanning Ion conductance microscopy (SICM). Factors which influence image quality and quantitatIon of Ion Currents measured with SICM have been evaluated. Specifically, effects of probe-sample separatIon and pipette modulatIon have been systematically studied for the case of imaging conductance variatIons at pores in a polymer membrane under transmembrane concentratIon gradients. The influence of probe-sample separatIon on Ion current images was evaluated using distance-modulated (ac) feedback. Approach curves obtained using non-modulated (dc) feedback were also recorded to determine the relative influence of pipette-generated convectIon by comparison of Ion Currents measured with both ac and dc feedback modes. To better interpret results obtained, comparison to a model based on a disk-shaped geometry for nanopores in the membrane, as well as relevant positIon-dependent parameters of the experiment is described. These results advance our current understanding of conductance measurements with SICM.
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measurement of Ion Currents through porous membranes with scanning Ion conductance microscopy
Analytical Chemistry, 2009Co-Authors: Chiaochen Chen, Maksymilian A Derylo, Lane A BakerAbstract:Scanning Ion conductance microscopy (SICM) was used to interrogate Ion Currents emanating from nanometer-scale pores of a polymer membrane. The transport activity of individual pores was measured by examining Ion current images and corresponding topographic images recorded simultaneously. Localized Ion Currents over individual nanopores were generated by introducing a concentratIon difference between the upper and lower chambers of a diffusIon cell. To better estimate these localized Ion Currents, Goldman−Hodgkin−Katz (GHK) theory was used to model Ion current through a permeable membrane under gradients of both concentratIon and applied potential. Experimental Ion current profiles over a single pore fit well with theoretical plots calculated from the GHK model. On the basis of this analysis, nanoscale transport properties can be measured with SICM.
Sunhye Choi - One of the best experts on this subject based on the ideXlab platform.
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differential effects of quercetin and quercetin glycosides on human α7 nicotinic acetylcholine receptor mediated Ion Currents
Biomolecules & Therapeutics, 2016Co-Authors: Sunhye Choi, Seokwon Jung, Sunghee Hwang, Hyewhon RhimAbstract:Quercetin is a flavonoid usually found in fruits and vegetables. Aside from its antioxidative effects, quercetin, like other flavonoids, has a various neuropharmacological actIons. Quercetin-3-O-rhamnoside (Rham1), quercetin-3-O-rutinoside (Rutin), and quercetin- 3-(2(G)-rhamnosylrutinoside (Rham2) are mono-, di-, and tri-glycosylated forms of quercetin, respectively. In a previous study, we showed that quercetin can enhance α7 nicotinic acetylcholine receptor (α7 nAChR)-mediated Ion Currents. However, the role of the carbohydrates attached to quercetin in the regulatIon of α7 nAChR channel activity has not been determined. In the present study, we investigated the effects of quercetin glycosides on the acetylcholine induced peak inward current (IACh) in Xenopus oocytes expressing the α7 nAChR. IACh was measured with a two-electrode voltage clamp technique. In oocytes injected with α7 nAChR copy RNA, quercetin enhanced IACh, whereas quercetin glycosides inhibited IACh. Quercetin glycosides mediated an inhibitIon of IACh, which increased when they were pre-applied and the inhibitory effects were concentratIon dependent. The order of IACh inhibitIon by quercetin glycosides was Rutin≥Rham1>Rham2. Quercetin glycosides-mediated IACh enhancement was not affected by ACh concentratIon and appeared voltage-independent. Furthermore, quercetin-mediated IACh inhibitIon can be attenuated when quercetin is co-applied with Rham1 and Rutin, indicating that quercetin glycosides could interfere with quercetin-mediated α7 nAChR regulatIon and that the number of carbohydrates in the quercetin glycoside plays a key role in the interruptIon of quercetin actIon. These results show that quercetin and quercetin glycosides regulate the α7 nAChR in a differential manner.
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resveratrol inhibits gabac ρ receptor mediated Ion Currents expressed in xenopus oocytes
The Korean Journal of Physiology and Pharmacology, 2013Co-Authors: Sunhye Choi, Sunghee HwangAbstract:Resveratrol is a phytoalexin found in grapes, red wine, and berries. Resveratrol has been known to have many beneficial health effects, such as anti-cancer, neuroprotective, anti-inflammatory, and life-prolonging effects. However, relatively little is known about the effects of resveratrol on the regulatIon of ligand-gated Ion channels. We have previously reported that resveratrol regulates subsets of homomeric ligand-gated Ion channels such as those of 5-HT3A receptors. The γ-aminobutyric acidC (GABAC) receptor is mainly expressed in retinal bipolar cells and plays an important role in visual processing. In the present study, we examined the effects of resveratrol on the channel activity of homomeric GABAC receptor expressed in Xenopus oocytes injected with cRNA encoding human GABAC ρ subunits. Our data show that the applicatIon of GABA elicits an inward peak current (IGABA) in oocytes that express the GABAC receptor. Resveratrol treatment had no effect on oocytes injected with H2O or with GABAC receptor cRNA. Co-treatment with resveratrol and GABA inhibited IGABA in oocytes with GABAC receptors. The inhibitIon of IGABA by resveratrol was in a reversible and concentratIon-dependent manner. The IC50 of resveratrol was 28.9±2.8 µM in oocytes expressing GABAC receptor. The inhibitIon of IGABA by resveratrol was in voltage-independent and non-competitive manner. These results indicate that resveratrol might regulate GABAC receptor expressIon and that this regulatIon might be one of the pharmacological actIons of resveratrol on the nervous system.
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inhibitory effects of ginsenoside metabolites compound k and protopanaxatriol on gabac receptor mediated Ion Currents
The Korean Journal of Physiology and Pharmacology, 2013Co-Authors: Sunghee Hwang, Sunhye ChoiAbstract:Ginsenosides, one of the active ingredients of Panax ginseng, show various pharmacological and physiological effects, and they are converted into compound K (CK) or protopanaxatriol (M4) by intestinal microorganisms. CK is a metabolite derived from protopanaxadiol (PD) ginsenosides, whereas M4 is a metabolite derived from protopanaxatriol (PT) ginsenosides. The γ-aminobutyric acid receptorC (GABAC) is primarily expressed in retinal bipolar cells and several regIons of the brain. However, little is known of the effects of ginsenoside metabolites on GABAC receptor channel activity. In the present study, we examined the effects of CK and M4 on the activity of human recombinant GABAC receptor (ρ1) channels expressed in Xenopus oocytes by using a 2-electrode voltage clamp technique. In oocytes expressing GABAC receptor cRNA, we found that CK or M4 alone had no effect in oocytes. However, co-applicatIon of either CK or M4 with GABA inhibited the GABA-induced inward peak current (IGABA). Interestingly, pre-applicatIon of M4 inhibited IGABA more potently than CK in a dose-dependent and reversible manner. The half-inhibitory concentratIon (IC50) values of CK and M4 were 52.1±2.3 and 45.7±3.9 µM, respectively. InhibitIon of IGABA by CK and M4 was voltage-independent and non-competitive. This study implies that ginsenoside metabolites may regulate GABAC receptor channel activity in the brain, including in the eyes.
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effects of protopanaxatriol ginsenoside metabolites on rat n methyl d aspartic acid receptor mediated Ion Currents
The Korean Journal of Physiology and Pharmacology, 2012Co-Authors: Taejoon Shin, Sunhye Choi, Sunghee Hwang, Jiyeon Kang, Suzanne R Zukin, Hyewhon RhimAbstract:Ginsenosides are low molecular weight glycosides found in ginseng that exhibit neuroprotective effects through inhibitIon of N-methyl-D-aspartic acid (NMDA) receptor channel activity. Ginsenosides, like other natural compounds, are metabolized by gastric juices and intestinal microorganisms to produce ginsenoside metabolites. However, little is known about how ginsenoside metabolites regulate NMDA receptor channel activity. In the present study, we investigated the effects of ginsenoside metabolites, such as compound K (CK), protopanaxadiol (PPD), and protopanaxatriol (PPT), on oocytes that heterologously express the rat NMDA receptor. NMDA receptor-mediated Ion current (INMDA) was measured using the 2-electrode voltage clamp technique. In oocytes injected with cRNAs encoding NMDA receptor subunits, PPT, but not CK or PPD, reversibly inhibited INMDA in a concentratIon-dependent manner. The IC50 for PPT on INMDA was 48.1±4.6 µM, was non-competitive with NMDA, and was independent of the membrane holding potential. These results demonstrate the possibility that PPT interacts with the NMDA receptor, although not at the NMDA binding site, and that the inhibitory effects of PPT on INMDA could be related to ginseng-mediated neuroprotectIon.
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effects of ginsenoside metabolites on gaba a receptor mediated Ion Currents
Journal of Ginseng Research, 2012Co-Authors: Sunhye Choi, Sunghee Hwang, Taejoon Shin, Jiyeon KangAbstract:In a previous report, we demonstrated that ginsenoside Rc, one of major ginsenosides from Panax ginseng, enhances γ-aminobutyric acid (GABA) receptorA (GABA A )-mediated Ion channel Currents. However, little is known about the effects of ginsenoside metabolites on GABA A receptor channel activity. The present study investigated the effects of ginsenoside metabolites on human recombinant GABA A receptor (α₁β₁γ 2s ) channel activity expressed in Xenopus oocytes using a two-electrode voltage clamp technique. M4, a metabolite of protopanaxatriol ginsenosides, more potently inhibited the GABA-induced inward peak current (I GABA ) than protopanaxadiol (PPD), a metabolite of PPD ginsenosides. The effect of M4 and PPD on I GABA was both concentratIon-dependent and reversible. The half-inhibitory concentratIon (IC??) values of M4 and PPD were 17.1±2.2 and 23.1±8.6 μM, respectively. The inhibitIon of I GABA by M4 and PPD was voltage-independent and non-competitive. This study implies that the regulatIon of GABA A receptor channel activity by ginsenoside metabolites differs from that of ginsenosides.
Chiaochen Chen - One of the best experts on this subject based on the ideXlab platform.
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effects of pipette modulatIon and imaging distances on Ion Currents measured with scanning Ion conductance microscopy sicm
Analyst, 2011Co-Authors: Chiaochen Chen, Lane A BakerAbstract:Local conductance variatIons can be estimated by measuring Ion current magnitudes with scanning Ion conductance microscopy (SICM). Factors which influence image quality and quantitatIon of Ion Currents measured with SICM have been evaluated. Specifically, effects of probe-sample separatIon and pipette modulatIon have been systematically studied for the case of imaging conductance variatIons at pores in a polymer membrane under transmembrane concentratIon gradients. The influence of probe-sample separatIon on Ion current images was evaluated using distance-modulated (ac) feedback. Approach curves obtained using non-modulated (dc) feedback were also recorded to determine the relative influence of pipette-generated convectIon by comparison of Ion Currents measured with both ac and dc feedback modes. To better interpret results obtained, comparison to a model based on a disk-shaped geometry for nanopores in the membrane, as well as relevant positIon-dependent parameters of the experiment is described. These results advance our current understanding of conductance measurements with SICM.
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measurement of Ion Currents through porous membranes with scanning Ion conductance microscopy
Analytical Chemistry, 2009Co-Authors: Chiaochen Chen, Maksymilian A Derylo, Lane A BakerAbstract:Scanning Ion conductance microscopy (SICM) was used to interrogate Ion Currents emanating from nanometer-scale pores of a polymer membrane. The transport activity of individual pores was measured by examining Ion current images and corresponding topographic images recorded simultaneously. Localized Ion Currents over individual nanopores were generated by introducing a concentratIon difference between the upper and lower chambers of a diffusIon cell. To better estimate these localized Ion Currents, Goldman−Hodgkin−Katz (GHK) theory was used to model Ion current through a permeable membrane under gradients of both concentratIon and applied potential. Experimental Ion current profiles over a single pore fit well with theoretical plots calculated from the GHK model. On the basis of this analysis, nanoscale transport properties can be measured with SICM.
Sunghee Hwang - One of the best experts on this subject based on the ideXlab platform.
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differential effects of quercetin and quercetin glycosides on human α7 nicotinic acetylcholine receptor mediated Ion Currents
Biomolecules & Therapeutics, 2016Co-Authors: Sunhye Choi, Seokwon Jung, Sunghee Hwang, Hyewhon RhimAbstract:Quercetin is a flavonoid usually found in fruits and vegetables. Aside from its antioxidative effects, quercetin, like other flavonoids, has a various neuropharmacological actIons. Quercetin-3-O-rhamnoside (Rham1), quercetin-3-O-rutinoside (Rutin), and quercetin- 3-(2(G)-rhamnosylrutinoside (Rham2) are mono-, di-, and tri-glycosylated forms of quercetin, respectively. In a previous study, we showed that quercetin can enhance α7 nicotinic acetylcholine receptor (α7 nAChR)-mediated Ion Currents. However, the role of the carbohydrates attached to quercetin in the regulatIon of α7 nAChR channel activity has not been determined. In the present study, we investigated the effects of quercetin glycosides on the acetylcholine induced peak inward current (IACh) in Xenopus oocytes expressing the α7 nAChR. IACh was measured with a two-electrode voltage clamp technique. In oocytes injected with α7 nAChR copy RNA, quercetin enhanced IACh, whereas quercetin glycosides inhibited IACh. Quercetin glycosides mediated an inhibitIon of IACh, which increased when they were pre-applied and the inhibitory effects were concentratIon dependent. The order of IACh inhibitIon by quercetin glycosides was Rutin≥Rham1>Rham2. Quercetin glycosides-mediated IACh enhancement was not affected by ACh concentratIon and appeared voltage-independent. Furthermore, quercetin-mediated IACh inhibitIon can be attenuated when quercetin is co-applied with Rham1 and Rutin, indicating that quercetin glycosides could interfere with quercetin-mediated α7 nAChR regulatIon and that the number of carbohydrates in the quercetin glycoside plays a key role in the interruptIon of quercetin actIon. These results show that quercetin and quercetin glycosides regulate the α7 nAChR in a differential manner.
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resveratrol inhibits gabac ρ receptor mediated Ion Currents expressed in xenopus oocytes
The Korean Journal of Physiology and Pharmacology, 2013Co-Authors: Sunhye Choi, Sunghee HwangAbstract:Resveratrol is a phytoalexin found in grapes, red wine, and berries. Resveratrol has been known to have many beneficial health effects, such as anti-cancer, neuroprotective, anti-inflammatory, and life-prolonging effects. However, relatively little is known about the effects of resveratrol on the regulatIon of ligand-gated Ion channels. We have previously reported that resveratrol regulates subsets of homomeric ligand-gated Ion channels such as those of 5-HT3A receptors. The γ-aminobutyric acidC (GABAC) receptor is mainly expressed in retinal bipolar cells and plays an important role in visual processing. In the present study, we examined the effects of resveratrol on the channel activity of homomeric GABAC receptor expressed in Xenopus oocytes injected with cRNA encoding human GABAC ρ subunits. Our data show that the applicatIon of GABA elicits an inward peak current (IGABA) in oocytes that express the GABAC receptor. Resveratrol treatment had no effect on oocytes injected with H2O or with GABAC receptor cRNA. Co-treatment with resveratrol and GABA inhibited IGABA in oocytes with GABAC receptors. The inhibitIon of IGABA by resveratrol was in a reversible and concentratIon-dependent manner. The IC50 of resveratrol was 28.9±2.8 µM in oocytes expressing GABAC receptor. The inhibitIon of IGABA by resveratrol was in voltage-independent and non-competitive manner. These results indicate that resveratrol might regulate GABAC receptor expressIon and that this regulatIon might be one of the pharmacological actIons of resveratrol on the nervous system.
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inhibitory effects of ginsenoside metabolites compound k and protopanaxatriol on gabac receptor mediated Ion Currents
The Korean Journal of Physiology and Pharmacology, 2013Co-Authors: Sunghee Hwang, Sunhye ChoiAbstract:Ginsenosides, one of the active ingredients of Panax ginseng, show various pharmacological and physiological effects, and they are converted into compound K (CK) or protopanaxatriol (M4) by intestinal microorganisms. CK is a metabolite derived from protopanaxadiol (PD) ginsenosides, whereas M4 is a metabolite derived from protopanaxatriol (PT) ginsenosides. The γ-aminobutyric acid receptorC (GABAC) is primarily expressed in retinal bipolar cells and several regIons of the brain. However, little is known of the effects of ginsenoside metabolites on GABAC receptor channel activity. In the present study, we examined the effects of CK and M4 on the activity of human recombinant GABAC receptor (ρ1) channels expressed in Xenopus oocytes by using a 2-electrode voltage clamp technique. In oocytes expressing GABAC receptor cRNA, we found that CK or M4 alone had no effect in oocytes. However, co-applicatIon of either CK or M4 with GABA inhibited the GABA-induced inward peak current (IGABA). Interestingly, pre-applicatIon of M4 inhibited IGABA more potently than CK in a dose-dependent and reversible manner. The half-inhibitory concentratIon (IC50) values of CK and M4 were 52.1±2.3 and 45.7±3.9 µM, respectively. InhibitIon of IGABA by CK and M4 was voltage-independent and non-competitive. This study implies that ginsenoside metabolites may regulate GABAC receptor channel activity in the brain, including in the eyes.
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effects of protopanaxatriol ginsenoside metabolites on rat n methyl d aspartic acid receptor mediated Ion Currents
The Korean Journal of Physiology and Pharmacology, 2012Co-Authors: Taejoon Shin, Sunhye Choi, Sunghee Hwang, Jiyeon Kang, Suzanne R Zukin, Hyewhon RhimAbstract:Ginsenosides are low molecular weight glycosides found in ginseng that exhibit neuroprotective effects through inhibitIon of N-methyl-D-aspartic acid (NMDA) receptor channel activity. Ginsenosides, like other natural compounds, are metabolized by gastric juices and intestinal microorganisms to produce ginsenoside metabolites. However, little is known about how ginsenoside metabolites regulate NMDA receptor channel activity. In the present study, we investigated the effects of ginsenoside metabolites, such as compound K (CK), protopanaxadiol (PPD), and protopanaxatriol (PPT), on oocytes that heterologously express the rat NMDA receptor. NMDA receptor-mediated Ion current (INMDA) was measured using the 2-electrode voltage clamp technique. In oocytes injected with cRNAs encoding NMDA receptor subunits, PPT, but not CK or PPD, reversibly inhibited INMDA in a concentratIon-dependent manner. The IC50 for PPT on INMDA was 48.1±4.6 µM, was non-competitive with NMDA, and was independent of the membrane holding potential. These results demonstrate the possibility that PPT interacts with the NMDA receptor, although not at the NMDA binding site, and that the inhibitory effects of PPT on INMDA could be related to ginseng-mediated neuroprotectIon.
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effects of ginsenoside metabolites on gaba a receptor mediated Ion Currents
Journal of Ginseng Research, 2012Co-Authors: Sunhye Choi, Sunghee Hwang, Taejoon Shin, Jiyeon KangAbstract:In a previous report, we demonstrated that ginsenoside Rc, one of major ginsenosides from Panax ginseng, enhances γ-aminobutyric acid (GABA) receptorA (GABA A )-mediated Ion channel Currents. However, little is known about the effects of ginsenoside metabolites on GABA A receptor channel activity. The present study investigated the effects of ginsenoside metabolites on human recombinant GABA A receptor (α₁β₁γ 2s ) channel activity expressed in Xenopus oocytes using a two-electrode voltage clamp technique. M4, a metabolite of protopanaxatriol ginsenosides, more potently inhibited the GABA-induced inward peak current (I GABA ) than protopanaxadiol (PPD), a metabolite of PPD ginsenosides. The effect of M4 and PPD on I GABA was both concentratIon-dependent and reversible. The half-inhibitory concentratIon (IC??) values of M4 and PPD were 17.1±2.2 and 23.1±8.6 μM, respectively. The inhibitIon of I GABA by M4 and PPD was voltage-independent and non-competitive. This study implies that the regulatIon of GABA A receptor channel activity by ginsenoside metabolites differs from that of ginsenosides.
Karl Kunzelmann - One of the best experts on this subject based on the ideXlab platform.
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regulatIon of tmem16a ano1 and tmem16f ano6 Ion Currents and phospholipid scrambling by ca2 and plasma membrane lipid
The Journal of Physiology, 2018Co-Authors: Rainer Schreiber, Jiraporn Ousingsawat, Podchanart Wanitchakool, Lalida Sirianant, Roberta Benedetto, Karina Reiss, Karl KunzelmannAbstract:TMEM16/anoctamin proteins form Ca2+ activated Ion channels or phospholipid scramblases. We found that both TMEM16A/ANO1 and TMEM16F/ANO6 produced Cl− Currents when activated by intracellular Ca2+, but only TMEM16F was able to expose phosphatidylserine to the outer leaflet of the plasma membrane. MutatIons within TMEM16F or TMEM16A/F chimeras similarly changed Cl− Currents and phospholipid scrambling, suggesting the same intramolecular pathway for Cl− and phospholipids. When overexpressed, TMEM16A and TMEM16F produced spontaneous Cl− Currents at 37°C even at resting intracellular Ca2+ levels, which was abolished by inhibitIon of phospholipase A2 (PLA2). Inversely, activatIon of PLA2 or applicatIon of active PLA2, as well as lipid peroxidatIon induced by reactive oxygen species (ROS) using staurosporine or tert-butyl hydroperoxide, enhanced Ion Currents by TMEM16A/F and in additIon activated phospholipid scrambling by TMEM16F. Thus TMEM16 proteins are activated by an increase in intracellular Ca2+, or independent of intracellular Ca2+ by modificatIons occurring in plasma and intracellular membrane phospholipids. These results may help to understand, why regIons distant to the TMEM16 pore and the Ca2+ binding sites control Cl− Currents and phospholipid scrambling. RegulatIon of TMEM16 proteins through modificatIon of membrane phospholipids occurs during regulated cell death such as apoptosis and ferroptosis. It contributes to inflammatory and nerve-injury induced hypersensitivity and generatIon of pain and therefore provides a regulatory mechanism particularly relevant during disease. This article is protected by copyright. All rights reserved
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calcium activated and apoptotic phospholipid scrambling induced by ano6 can occur independently of ano6 Ion Currents
Cell Death and Disease, 2013Co-Authors: Arthur Kmit, Jiraporn Ousingsawat, R Van Kruchten, Nadine J A Mattheij, Birgit L M G Sendengijsbers, Johan W M Heemskerk, R Schreiber, Edouard M Bevers, Karl KunzelmannAbstract:Immune cells and platelets maintain plasma membrane phospholipid asymmetry. Upon activatIon, this asymmetry is disrupted by phospholipid scrambling (PS), which is a major step during activatIon of immune cells, hemostasis and apoptosis. Anoctamin 6 (Ano6; TMEM16F) causes chloride (Cl−) and catIon Currents and is required for Ca2+-dependent PS. It is defective in blood cells from patients with Scott syndrome, a rare bleeding disorder. We examined if Cl− Currents and PS are related, whether both processes are Ca2+ dependent, and whether Ca2+-independent scrambling during intrinsic and extrinsic apoptosis is controlled by Ano6. Ca2+ increase by Ionomycin activated Ano6 Cl− Currents and PS in normal lymphocytes, but not in B-lymphocytes from two different patients with Scott syndrome. Fas ligand (FasL) did not increase intracellular Ca2+, but activated Cl− Currents in normal but not in Scott lymphocytes. Whole-cell Currents were inhibited by Cl− channel blockers and by siRNA knockdown of Ano6. In contrast, intrinsic mitochondrial apoptosis by ABT-737 did not induce Cl− Currents in lymphocytes. PS was not inhibited by blockers of Ano6 or removal of Cl− Ions. Remarkably, Ca2+-independent scrambling due to extrinsic (FasL) or intrinsic (ABT-737) apoptosis was unchanged in Scott cells. We conclude that: (i) Ano6 Cl− Currents are activated by increase in cytosolic Ca2+, or Ca2+ independent by stimulatIon of Fas receptors; (ii) Ca2+-dependent PS induced by Ano6 does not require Cl− Currents; (iii) Ca2+-independent PS does not require Ano6; (iv) Ano6 is necessary for Ca2+-dependent PS, but not by increasing intracellular Ca2+.
