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PubMed1995

Changes in membrane potential during the progression of MCF-7 human mammary tumor cells through the cell cycle.

We previously reported that MCF-7 cells were arrested in the G0/G1 phase of the cell cycle by agents known to block the activity of ATP-sensitive potassium channels (Woodfork et al., 1995, J. Cell Physiol. 162:163-171). The goal of our current study was to determine if MCF-7 cells undergo changes in membrane potential during the cell cycle that might be linked to changes in K permeability. The resting membrane potentials of unsynchronized MCF-7 cells during exponential growth phase were measured using sharp glass microelectrodes, and they ranged from -58.6 mV to -2.7 mV. The distribution of membrane potentials was best fitted by the sum of four Gaussian distributions with means of -9.0 mV, -17.4 mV, -24.6 mV, and -40.4 mV. These membrane potential groups were designated D (depolarized), ID (intermediate depolarized), IH (intermediate hyperpolarized), and H (hyperpolarized), respectively. The membrane potential was sensitive to the substitution of external K and Na but not Cl. The K:Na permeability ratio increased in proportion to the negativity of the membrane potential. MCF-7 cells pharmacologically arrested in G0/G1 phase were depolarized compared to control, with cells shifted from the H and IH groups to the D group. Tamoxifen-arrested cells chased from G0/G1 into S phase by the addition of mitogenic concentrations of 17 beta-estradiol were not depolarized, and these cells were shifted from the D group back to the IH and H groups. We conclude that MCF-7 cells hyperpolarize during passage through G0/G1 and into S phase, and this hyperpolarization probably results from an increase in the relative permeability of the plasma membrane to K.

Breast Neoplasms↗
PubMed1979

Optical probes of membrane potential in heart muscle.

1. The fluorescent dye Merocyanine-540 and the two weakly fluoresecnet dyes Merocyanine-rhodanine and Merocyanine-oxazolone are shown to respond as optical probes of membrane potential in heart muscle. 2. In frog hearts stained with Merocyanine-540, the absorption at 540 nm decreases by 0.1-1.0% and increase at 570 nm excitation wave-length, the fluorescence increases by 1-2%. The time course of all three optical measurements follows the kinetics of the action potential. 3. Merocyanine-rhodanine exhibits potential-dependent optical responses through a 0.5% decrease in absorption at 750 nm, and Merocyanine-oxazolone has a 1.0% decrease in absorption at 720 nm. Their optical responses have a signal-to-noise ratio of 100/1 and 500/1, respectively. 4. The action spectrum of Merocyanine-rhodanine is triphasic in frog heart with an increase in transmittance from 780 to 700, a decrease from 700 to 600, and increase from 600 to 450 nm. Merocyanine-oxazolone shows only increases in transmittance during membrane depolarization. 5. The optical responses of these probes are linear with respect to changes in membrane potential. 6. Pharmacological agents or ionic interventions do not alter the membrane potential sensitivity of Merocyanine-540. 7. Rapid spectrophotometric measurements at various phases of the action potential indicate that the potential dependent optical signals of Merocyanine-540 are produced by changes in amplitude of fluorescence and absorption bands. The lack of wave-length displacement as a function of membrane potential, i.e. electrochromism, is not the mechanism governing the voltage sensitivity of Merocyanine-540. 8. The data suggest that these Merocyanine dyes bind to the plasma membrane and serve as linear optical probes of membrane potential in heart muscle.

Animals↗
PubMed2000

Subthreshold oscillation of the membrane potential in magnocellular neurones of the rat supraoptic nucleus.

Electrophysiological properties and ionic basis of subthreshold oscillation of the membrane potential were examined in 104 magnocellular neurones of the rat supraoptic nucleus using intracellular recording techniques in a brain slice preparation. Subthreshold oscillation of the membrane potential occurring in all neurones examined was voltage dependent. Oscillation was initiated 7-12 mV negative to the threshold of fast action potentials. Oscillation was the result of neither excitatory nor inhibitory synaptic activity nor of electric coupling. Frequency analyses revealed a broad band frequency distribution of subthreshold oscillation waves (range 10-70 Hz). The frequency band of 15-33 Hz was observed in neurones depolarized close to the threshold of discharge. Subthreshold oscillation was blocked by TTX (1.25-2.5 microM) as well as by TEA (15 mM). Subthreshold oscillation was not blocked by low Ca(2+)-high Mg(2+) superfusate, CdCl(2), TEA (1-4.5 mM), 4-aminopyridine, apamin, charybdotoxin, iberiotoxin, BaCl(2), carbachol and CsCl. During application of TTX, stronger depolarization induced high-threshold oscillation of the membrane potential at a threshold of about -32 mV. These oscillation waves occurred at a mean frequency of about 35 Hz and were blocked by CdCl(2). Effects of ion channel antagonists suggest that subthreshold oscillation is generated by the interaction of a subthreshold sodium current and a subthreshold potassium current. The generation of high-threshold oscillation during TTX involves a high-threshold calcium current. Subthreshold oscillation of the membrane potential may be important for the inter-neuronal synchronization of discharge and for the amplification of synaptic events.

Anesthetics, Local↗
PubMed1987

Insulin-induced changes in membrane potential and 3-O-methylglucose uptake at various external K concentrations in frog skeletal muscle.

Insulin induced a hyperpolarization of the membrane and stimulated the 3-O-methylglucose (3-O-MG) uptake in frog skeletal muscle. In the present study, the relationship between the insulin-induced changes in the membrane potential and the 3-O-MG uptake was investigated. The stimulatory action of insulin on the 3-O-MG uptake was mediated by two different mechanisms. One of them was dependent on the change in the membrane potential and the other was independent of the change in the membrane potential. Both values of the insulin-induced changes in the membrane potential and the 3-O-MG uptake were diminished by increasing the external K concentration. One of the causes for the diminution of the 3-O-MG uptake with a rise of the external K concentration would be the decrease in the magnitude of the insulin-induced hyperpolarization.

3-O-Methylglucose↗
PubMed1992

Airway epithelial cells regulate membrane potential, neurotransmission and muscle tone of the dog airway smooth muscle.

1. The effects of epithelial cells were investigated on resting membrane potential and neuro-effector transmission in smooth muscle cells of the dog tracheal and bronchiolar tissues. 2. The mean value of the resting membrane potential of the epithelium-intact bronchiolar smooth muscle cells of the dog was--70.0 +/- 1.1 mV (+/- S.D., n = 40) and mechanical denudation of the epithelial layer depolarized the membrane to -57.0 +/- 2.5 mV (+/- S.D., n = 40). Application of isolated and dispersed epithelial cells (greater than 2 x 10(5) cells/ml) to the perfusing solution repolarized the membrane of epithelium-denuded bronchiolar smooth muscle cells to -67.0 +/- 2.7 mV (+/- S.D., n = 20). The mean resting membrane potential of the mucosa-free tracheal smooth muscle cells was -59.1 +/- 1.4 mV (+/- S.D., n = 50), and application of isolated and dispersed cells (greater than 2 x 10(5) cells/ml) hyperpolarized the membrane to -67.2 +/- 1.8 mV (+/- S.D., n = 50). These repolarizing actions were not modified by indomethacin (10(-5) M). 3. In the epithelium-denuded bronchioles, ACh (greater than 10(-9) M) dose-dependently depolarized the smooth muscle cells, while in the epithelium-intact bronchioles, ACh (10(-11) - 10(-8) M) did not affect the resting membrane potential. At a concentration of 10(-7) M, ACh significantly depolarized the membrane. 4. Electrical field stimulation (EFS; 50 microseconds in duration and about 10-20 V in strength) applied to ring preparations of the bronchioles evoked twitch-like contractions (hereafter referred as twitch contraction), and size of the twitch contractions gradually and continuously decreased in the presence or absence of indomethacin (10(-5) M) and guanethidine (10(-6) M). When similar experiments were performed using epithelium-denuded bronchiolar ring preparations, in no case was there a prominent reduction in the amplitude of the twitch contractions in the presence of indomethacin and guanethidine. 5. The decremental response of the twitch contraction observed in the epithelium-intact bronchioles was overcome by application of the leukotriene synthesis inhibitor AA861 (10(-6) M) and the leukotriene antagonist ONO1078 (10(-5) M). 6. Leukotrienes C4 and D4 (LTC4 and LTD4, greater than 10(-8) M) evoked muscle contraction with a steady increase in muscle tone, up to a certain level. However, at 10(-9) M, LTC4 increased and LTD4 decreased the amplitude of the twitch contractions evoked by EFS in the epithelium-intact bronchioles.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2000

Absence of cardiolipin in the crd1 null mutant results in decreased mitochondrial membrane potential and reduced mitochondrial function.

Cardiolipin (CL) is a unique phospholipid which is present throughout the eukaryotic kingdom and is localized in mitochondrial membranes. Saccharomyces cerevisiae cells containing a disruption of CRD1, the structural gene encoding CL synthase, have no CL in mitochondrial membranes. To elucidate the physiological role of CL, we compared mitochondrial functions in the crd1Delta mutant and isogenic wild type. The crd1Delta mutant loses viability at elevated temperature, and prolonged culture at 37 degrees C leads to loss of the mitochondrial genome. Mutant membranes have increased phosphatidylglycerol (PG) when grown in a nonfermentable carbon source but have almost no detectable PG in medium containing glucose. In glucose-grown cells, maximum respiratory rate, ATPase and cytochrome oxidase activities, and protein import are deficient in the mutant. The ADP/ATP carrier is defective even during growth in a nonfermentable carbon source. The mitochondrial membrane potential is decreased in mutant cells. The decrease is more pronounced in glucose-grown cells, which lack PG, but is also apparent in membranes containing PG (i.e. in nonfermentable carbon sources). We propose that CL is required for maintaining the mitochondrial membrane potential and that reduced membrane potential in the absence of CL leads to defects in protein import and other mitochondrial functions.

Cardiolipins↗
PubMed1995

Subthreshold membrane-potential oscillations in immature rat CA3 hippocampal neurones.

Subthreshold membrane potential oscillations (MPOs) were recorded intracellularly in 31 of 43 (>70%) immature CA3 hippocampal neurones (from 3-17 days postnatally). MPOs (3-5 mV, 3-15 Hz) occurred at resting membrane potential (RMP) in 20 of 31 neurones, or following depolarization (11 of 31 neurones); with sufficient depolarization spontaneous action potentials (APs) were generated from the positive-going phase of MPOs. In all cells, MPOs were blocked by steady membrane hyperpolarization. Tetrodotoxin abolished MPOs (n = 4); Co(2+) markedly reduced them (n = 3), and tetraethylammonium, added in the presence of TTX, revealed lower frequency oscillatory activity (n = 2). We conclude that subthreshold MPOs in immature hippocampus, possibly linked to theta rhythm generation and memory acquisition, depend on voltage-dependent Na+ electrogenesis and they might be additionally controlled by Ca(2+) and K+ conductances.

Animals↗
PubMed1998

Membrane potential responses of paramecium caudatum to bitter substances: existence of multiple pathways for bitter responses

The membrane potential responses of Paramecium caudatum to the external application of bitter substances were examined by employing conventional electrophysiological techniques. Mutant cells defective in voltage-gated Ca2+ channels were used to record the potential responses in the absence of contamination by Ca2+ action potentials. The cells produced a transient depolarization followed by a transient hyperpolarization in response to a rapid whole-cell application of chloroquine, strychnine nitrate or brucine. Of these chemicals, chloroquine was the most potent. Cells produced a simple depolarization in response to a localized application of test chemicals to the anterior region, whereas they produced a transient hyperpolarization in response to an application to the posterior region. Membrane potential responses to an application of chloroquine declined with repeated application. The presence of chloroquine in the external bathing solution strongly inhibited the membrane potential responses to an application of brucine or strychnine. However, the presence of chloroquine did not affect the membrane potential responses to an application of quinine. It is suggested that chloroquine, strychnine and brucine share a common component of their transduction pathways, but that the transduction pathway for quinine is different.

Journal Article↗
PubMed2001

Hamster oocyte membrane potential and ion permeability vary with preantral cumulus cell attachment and developmental stage.

BACKGROUND: In vitro maturation of mammalian oocytes is an area of great interest due to its potential application in the treatment of infertility. The morphological and physiological changes that occur during oocyte development are poorly understood, and further studies are needed investigating the physiological changes associated with oocyte maturation. In this study we evaluated the membrane potential and the sodium/potassium permeability ratio of oocytes acutely isolated, and cumulus-oocyte complexes in metaphase II and preantral follicle stages. RESULTS: Intracellular electrical recordings revealed that cumulus-enclosed oocytes have a membrane potential significantly more negative at the preantral follicle stage than at metaphase II stage (-38.4 versus -19.7 mV, p < 0.0005). The membrane potential of the cumulus-free oocytes was not different between the preantral and metaphase II stages. The membrane potential of the cumulus cells forming preantral stage follicles was shown to be significantly different from that of the oocyte within the follicle (-28.6 versus -38.4 mV, p < 0.05). The sodium/potassium permeability measured in cumulus-enclosed oocytes at the preantral stage equaled a mean value of 0.33. The ratio was significantly lower when measured in oocytes denuded of cumulus cells or cumulus-enclosed metaphase II oocytes, 0.76, 0.79, 0.77 respectively (p < 0.001). CONCLUSIONS: These data show a change in the membrane potential and Na+/K+ permeability ratio during ooycte development from the preantral stage oocyte to the metaphase II stage. We have also demonstrated a change in the preantral oocyte membrane potential when surrounding cumulus cells are removed; either due to membrane changes or loss of cumulus cells.

Animals↗
PubMed1993

A new method for the cytofluorimetric analysis of mitochondrial membrane potential using the J-aggregate forming lipophilic cation 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolcarbocyanine iodide (JC-1).

A new method for the cytofluorimetric analysis of mitochondrial membrane potential in intact cells has been developed by using the lipophilic cationic probe 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolcarbocyanine iodide (JC-1), whose monomer emits at 527 nm after excitation at 490 nm. Depending on the membrane potential, JC-1 is able of forming J-aggregates that are associated with a large shift in emission (590 nm). The color of the dye changes reversibly from green to greenish orange as the mitochondrial membrane becomes more polarized. In two human cell lines (K562 and U937), we have studied by flow cytometry the changes in membrane potential provoked by the K+ ionophor valinomycin, a drug known to affect mitochondrial membrane potential, while the K+/H+ ionophor nigericin, known to affect intracellular pH but not mitochondrial membrane potential, was used as control. The incubation with valinomycin for 10 min. at 37 degrees C in a low K+ medium provoked a marked and dose-dependent reduction in JC-1 greenish orange fluorescence, while nigericin had no effect.

Benzimidazoles↗
PubMed1983

Membrane potentials of urinary bladder epithelium in F344 rats treated with N-butyl-N-(4-hydroxybutyl)nitrosamine or sodium saccharin.

Membrane potentials of the urinary bladder epithelium in F344 male rats treated with N-butyl-N-(4-hydroxybutyl)-nitrosamine (BBN) or sodium saccharin were measured. In experiment 1, membrane potentials were measured sequentially in the early stage of their change on treatment with 0.05% BBN in the drinking water or with basal diet containing 5% sodium saccharin. Membrane potentials were measured with microelectrodes in weeks 1, 2, 4 and 8 of the experiment. The potential of the group treated with BBN was significantly higher than that of the controls from as early as week 1 until the end of the experiment. In experiment 2, the dose-dependence of the effects of BBN and sodium saccharin on the membrane potential was examined. F344 male rats were treated with 0.05, 0.01, 0.005 or 0.001% BBN in the drinking water, or 5, 1, 0.2 or 0.04% sodium saccharin in basal diet. Clear dose-dependence was observed in the effect of BBN on the potential, but of the doses of sodium saccharin used, only 5% saccharin caused a significantly higher potential than in the control group. These findings suggested that in the early stage of urinary bladder carcinogenesis induced by BBN, the Na+ channel located in the apical membrane may be inactivated.

Animals↗
PubMed2006

The adenosine 5'-triphosphate-sensitive potassium channel in endocrine cells of the human ovary: role in membrane potential generation and steroidogenesis.

CONTEXT: ATP-sensitive potassium (K(ATP)) channels couple the metabolic state with the membrane potential in several cell types, and recently evidence for K(ATP) channels was given in rat corpus luteum, a fast-growing and metabolically highly active tissue. OBJECTIVE: We studied whether K(ATP) channels are present in the human ovary and luteinized granulosa cells (GCs). Human GCs were examined regarding functionality and physiological role of the channel. PATIENTS AND INTERVENTION: Human GCs were obtained from in vitro fertilization patients. RESULTS: K(ATP) channels are involved in membrane potential generation in human GCs because application of the K(ATP) blocker glibenclamide resulted in depolarization as monitored by fluorescence microscopy. Furthermore, glibenclamide significantly attenuated human chorionic gonadotropin-induced progesterone production. The channel pore is composed of K(ir)6.1, but not K(ir)6.2, as indicated by RT-PCR. K(ir)6.1 subunit protein was detected in human follicular and luteal cells by immunohistochemistry and localized to the plasma membrane of human GCs by immunogold staining. RT-PCR experiments revealed the sulfonylurea receptor subunit SUR2B as part of the K(ATP) channel. In addition, mRNAs encoding SUR1 and SUR2A were detected in some preparations. There is no evidence for mitochondrial K(ATP) channels in human GCs because we detected neither K(ir)6.1 protein in mitochondrial membranes nor alterations of mitochondrial membrane potential by glibenclamide or the K(ATP) opener diazoxide. CONCLUSIONS: Endocrine cells of the human ovary possess functional K(ATP) channels, which are linked to both plasma membrane potential generation and progesterone production. Our results may provide new insights into human ovarian physiology and raise the possibility of pharmacological targeting.

ATP-Binding Cassette Transporters↗
PubMed1990

Effect of mitochondrial and plasma membrane potentials on accumulation of hexakis (2-methoxyisobutylisonitrile) technetium(I) in cultured mouse fibroblasts.

Hexakis(2-methoxyisobutylisonitrile) technetium(I) (Tc-MIBI) is representative of a class of 99mTc-based lipophilic cationic myocardial perfusion imaging agents. To test the hypothesis that the mechanism of cellular uptake may involve distribution across biologic membranes in response to membrane potential, Tc-MIBI net uptake and retention were determined in cultured mouse BALB/c 3T3, NIH 3T3, and v-src transformed NIH 3T3 fibroblasts as well as in cultured chick embryo heart cells. Isovolumic depolarization of plasma membrane potentials with 130 mM K 20 mM Cl buffer decreased Tc-MIBI net cell uptake in all preparations. In BALB/c 3T3 cells, depolarizing mitochondrial membrane potential with valinomycin in high K buffer or with the protonophore CCCP inhibited net uptake and retention of Tc-MIBI while hyperpolarizing mitochondrial and plasma membrane potentials with the K+/H+ exchanger nigericin increased Tc-MIBI net uptake. These results indicated that net cellular uptake and retention of Tc-MIBI in fibroblasts were determined by both mitochondrial and plasma membrane potentials; the gamma-emitting properties of Tc-MIBI may therefore raise the possibility of monitoring membrane potential in vivo.

Animals↗
PubMed1988

Steady-state and transient membrane potentials in human red cells determined by protonophore-mediated pH changes.

Protonophores have been used frequently to determine changes in membrane potential in suspensions of red cells, since such changes are reflected by changes in extracellular pH, due to proton and consequently protonophore reequilibration. In a previous paper (Bennekou, P. 1988, J. Membrane Biol. 102:225-234) a kinetic model for the translocation of a protonophore, CCCP, across the human red cell membrane was established. This model accounts for the protonophore reequilibration following abrupt changes in membrane potential. In this paper the limitations of the method with regard to the estimation of transient membrane potentials are examined, using the transport model to simulate changes in extracellular pH in response to noninstantaneous changes in membrane potential. The temperature and time resolution calculated from the model are reported. Furthermore, it is shown that the transport model established for CCCP is valid for another protonophore, TCS, thus indicating the general validity of the transport scheme for the entire class of protonophores.

Carbonyl Cyanide m-Chlorophenyl Hydrazone↗
PubMed1992

The effects of ethanol on intracellular potassium and the membrane potential of an identified crab motor axon.

1. Observations were made on the fast bender excitor axon in autotomized crab walking limbs bathed in normal crab saline, and in salines made up with 0.2 M sucrose or 0.2 M ethanol. Microelectrode techniques were used to measure the resting membrane potential and the intracellular level of potassium. 2. Sucrose-saline had little effect on the membrane potential or the intracellular level of potassium. Ethanol-saline hyperpolarized the membrane potential by about 3 mV and increased the level of intracellular potassium. 3. The ethanol-induced changes in intracellular potassium levels and membrane potential took place with the same time course. Further, the changes in membrane potential could be accounted for by changes in the equilibrium potential for potassium, Ek as predicted by the Nernst equation.

Action Potentials↗
PubMed1980

Effects of ionophores and metabolic inhibitors on the mitochondrial membrane potential within isolated hepatocytes as measured with the safranine method.

A difference spectrum with a peak of absorbance at 526nm appears slowly upon addition of valinomycin or KCN in combination with oligomycin to a hepatocyte suspension in the presence of safranine. When the cells are incubated at 37 degrees C in a medium containing safranine, a slow decrease in the absorbance occurs at the wavelength pair 524-484 nm. The change in absorbance is completed within 20-30 min after additions of cells to a medium containing safranine. At this time the safranine concentration of the outer medium is considerably decreased. The safranine signal is completely reversed by valinomycin, carbonyl cyanide p-trifluoromethoxyphenyl-hydrazone or KCN in combination with oligomycin. None of these treatments have any immediate effect on cellular ATP concentrations or the 36Cl- equilibrium potential across the plasma membrane. In the presence of iodoacetate a slow reversal of the trace can be induced upon addition of KCN, but not of oligomycin alone. Rotenone, in combination with oligomycin, does not reverse the safranine signal except when both KF and iodoacetate are present, in which case a slow reversal is seen. A subsequent addition of duroquinone brings back the signal to the same level as in the presence of rotenone alone. The results indicate that the spectral response of safranine in the presence of isolated hepatocytes is a result of a slow penetration of safranine into intracellular mitochondria, where aggregation of safranine molecules occurs as a response to the mitochondrial membrane potential.

Animals↗
PubMed2000

The membrane potential of Giardia intestinalis.

Giardia intestinalis is a primitive microaerophilic protozoan parasite which colonises the upper intestine of humans. Despite the evolutionary and medical significance of this organism, its physiology is very poorly understood. In this study we have used a novel flow cytometric technique to make quantitative measurements of the electrical potential across the plasma membrane of G. intestinalis trophozoites. In media lacking both K(+) and Na(+), G. intestinalis trophozoites maintained a high negative plasma membrane potential (Psi(m)) of -134+/-3 mV. The Psi(m) was unaffected by the addition of Na(+) to the extracellular medium, whereas the addition of K(+) resulted in a significant membrane depolarisation, consistent with the G. intestinalis trophozoite plasma membrane having a significant (electrophoretic) permeability to K(+). The membrane was also depolarised by the H(+) ionophore m-chlorophenylhydrazone and by the H(+) ATPase inhibitors dicyclohexylcarbodiimide and N-ethylmaleimide. These results are consistent with G. intestinalis trophozoites maintaining a high resting Psi(m), originating at least in part from an electrogenic H(+) pump acting in concert with a K(+) diffusion pathway.

Animals↗
PubMed1988

Liposomes as model for taste cells: receptor sites for bitter substances including N-C=S substances and mechanism of membrane potential changes.

Various bitter substances were found to depolarize liposomes. The results obtained are as follows: (1) Changes in the membrane potential of azolectin liposomes in response to various bitter substances were monitored by measuring changes in the fluorescence intensity of 3,3'-dipropylthiocarbocyanine iodide [diS-C3(5)]. All the bitter substances examined increased the fluorescence intensity of the liposome-dye suspension, which indicates that the substances depolarize the liposomes. There existed a good correlation between the minimum concentrations of the bitter substances to depolarize the liposomes and the taste thresholds in humans. (2) The effects of changed lipid composition of liposomes on the responses to various bitter substances vary greatly among bitter substances, suggesting that the receptor sites for bitter substances are multiple. The responses to N-C=S substances and sucrose octaacetate especially greatly depended on the lipid composition; these compounds depolarized only liposomes having certain lipid composition, while no or hyperpolarizing responses to these compounds were observed in other liposomes examined. This suggested that the difference in "taster" and "nontaster" for these substances can be explained in terms of difference in the lipid composition of taste receptor membranes. (3) It was confirmed that the membrane potential of the planar lipid bilayer is changed in response to bitter substances. The membrane potential changes in the planar lipid bilayer as well as in liposomes in response to the bitter substances occurred under the condition that there is no ion gradient across the membranes. These results suggested that the membrane potential changes in response to bitter substances stem from the phase boundary potential changes induced by adsorption of the substances on the hydrophobic region of the membranes.

Benzothiazoles↗