Transmembrane Potential Of Cells Research Articles

The Effect of Hyperthermia on Transmembrane Potential in Chinese Hamster Ovary Cells in Vitro

The effect of elevated temperature on transmembrane potential was studied in Chinese hamster ovary cells in vitro using tetraphenylphosphonium cation (TPP+) and 3,3'-dipentyloxacarbocyanine [Di-O-C5(3)], two unrelated lipophilic cation probes that equilibrate across the plasma membrane according to the transmembrane potential. Uptake of TPP+ was measured using a tritium-labeled probe and the uptake of the fluorescent probe Di-O-C5(3) was measured by flow cytometry. The Nernst equation was used to calculate transmembrane potential. The absolute values obtained for transmembrane potential at 37 degrees C using the two probes were different, but qualitatively similar results were obtained using either probe in the hyperthermia studies. Transmembrane potential measured at 43 and 45 degrees C was at least 20% higher than that measured at 37 degrees C, and the difference was statistically significant (P = 0.025 and P less than 0.01, respectively). The hyperpolarization induced by exposure to 45 degrees C persisted temporarily after cells had been returned to 37 degrees C. The hyperpolarization at 37 degrees C associated with a previous exposure to hyperthermia was maximal after cells had been held at 45 degrees C for 2.0 min, and fell to normal levels after 15.0 min at 37 degrees C.

Effect of tetrodotoxin on the transmembrane potential of the pacemaker cell in the sinus venosus of toad

Transmembrane potentials of single pacemaker cells in the sinus venosus of toad have been recorded with floating microelectrode, and it was found that the action potential amplitudes were not identical in different pacemaker cells. In the recorded potential range of maximum diastolic potential (MDP) 40 – 75 mv, there was a linear correlation between MDP and maximum upstroke velocity (Vmax) (r = 0.80, n = 16), and cells with different MDP reacted differently to tetrodotoxin (TTX). When MDP was equal to or less than 56 mv, the transmembrane potential did not show any significant change after TTX; when the MDP was higher than 56 mv, the transmembrane potential exhibited significant changes, mainly in reduction of APA and Vmax after TTX. The experimental results indicate that, when MDP is below 56 mv, the fast sodium channels are totally inactivated, whereas with MDP higher than 56 mv some of the fast sodium channels are available and contribute to the rising phase of the action potential.

Effects of anisosmotic medium on cell volume, transmembrane potential and intracellular K+ activity in mouse hepatocytes.

Mouse hepatocytes in primary monolayer culture (4 hr) were exposed for 10 min at 37 degrees C to anisosmotic medium of altered NaCl concentration. Hepatocytes maintained constant relative cell volume (experimental volume/control volume) as a function of external medium relative osmolality (control mOsm/experimental mOsm) ranging from 0.8 to 1.5. In contrast, the relative cell volume fit a predicted Boyle-Van't Hoff plot when the experiment was done at 4 degrees C. Mouse liver slices were used for electrophysiologic studies, in which hepatocyte transmembrane potential (Vm) and intracellular K+ activity (aik) were recorded continuously by open-tip and liquid ion-exchanger ion-sensitive glass microelectrodes, respectively. Liver slices were superfused with control and then with anisosmotic medium of altered NaCl concentration. Vm increased (hyperpolarized) with hypoosmotic medium and decreased (depolarized) with hyperosmotic medium, and in [10(experimental Vm/control Vm)] was a linear function of relative osmolality (control mOsm/experimental mOsm) in the range 0.8-1.5. The aik did not change when medium osmolality was decreased 40-70 mOsm from control of 280 mOsm. Similar hypoosmotic stress in the presence of either 60 mM K+ or 1 mM quinine HCl or at 27 degrees C resulted in no change in Vm compared with a 20-mV increase in Vm without the added agents or at 37 degrees C. We conclude that mouse hepatocytes maintain their volume and aik in response to anisosmotic medium; however, Vm behaves as an osmometer under these conditions. Also, increases in Vm by hypoosmotic stress were abolished by conditions or agents that inhibit K+ conductance.

Delta-opioid receptors mediate inhibition of fast excitatory postsynaptic potentials in cat parasympathetic colonic ganglia.

1 The effects of opioids on synaptic transmission in cat sacral parasympathetic colonic ganglia were studied in vitro, using intracellular electrophysiological techniques. Electrical stimulation of the pelvic nerve evoked fast excitatory postsynaptic potentials (e.p.s.ps), which were blocked by hexamethonium and tetrodotoxin. 2 [D-Pen2, D-Pen5] enkephalin and [Met5]enkephalinamide, delta-opioid receptor agonists, caused concentration-dependent, reversible depression of fast e.p.s.ps, but had no effect on depolarizations evoked by pressure ejection of the nicotinic agonist 1,1-dimethyl-4-phenyl-piperazinium. Cell transmembrane potential and membrane input resistance were also unaffected. 3 U-50,488H, a kappa-opioid receptor agonist, had a very small depressant action while [D-Ala2, MePhe4, Gly-ol5] enkephalin, a mu-opioid receptor agonist, had no effect on fast e.p.s.p. amplitude. Neither compound affected cell transmembrane potential or membrane input resistance. 4 The inhibitory actions of [D-Pen2, D-Pen5] enkephalin were antagonized by both naloxone, an antagonist at each of the three opioid receptor types, and by ICI 174,864, an antagonist selective for delta-opioid receptors. 5 Naloxone and ICI 174,864 both also potentiated fast e.p.s.p. amplitude per se in 50% of cells tested. 6 It is concluded that exogenous opioids act at presynaptic delta-opioid receptors to inhibit sacral parasympathetic synaptic transmission in cat colonic ganglia in vitro. Furthermore, the effects of opioid antagonists alone, suggest that endogenous opioids may also be released by preganglionic nerve stimulation and so regulate the release of acetylcholine in these ganglia.

Effect of cold on transmembrane potentials in cardiac cells of the hedgehog

1. 1. Transmembrane potentials and their characteristics were studied in right ventricular cells of the hedgehog between 35 and 0°C 2. 2. When temperature decreased below 35°C, the maximal rate of depolarization declined and action potential duration prolonged markedly. The overshoot disappeared at about 5°C and the action potential became a slow responsive type at low temperature. There was no significant change in the amplitude of action potential (APA) and resting potential (RP) above 20°C; between 20 and 0°C both showed a steady decline to about 40–55 and 70–80% of their maxima at 35°C respectively. RP and ADA were significantly higher in summer active than in winter hibernating animals. However, no significant difference was seen between the hibernating and active animals in winter 3. 3. At 35°C, increasing extracellular Ca 2+ from 2.7 (normal) to 16.2 mM did not affect APA, and it was only slightly decreased in Ca 2+free solution 4. 4. At 5°C, APA increased to a plateau with rise of extra cellular Ca 2+ between 0.5 to 8.1 mM and it dropped to zero in Ca 2+free solution 5. 5. It is concluded that the cardiac cell membrane of the hedgehog maintains its excitability at 10°C and the slow Ca 2+ channel may play an important role in cardiac excitation at low temperature.

Effect of Some Anticancer Drugs on the Surface Membrane Electrical Properties of Differentiated Murine Neuroblastoma Cells<xref ref-type="fn" rid="FN2">2</xref>

The effect of some anticancer agents that produce toxic effects on electrically excitable cells in vivo was studied in vitro with the use of differentiated N1E-115 murine neuroblastoma cells and single microelectrode electrical recording. In the presence of 10(-7) g/ml tetrodotoxin, following the release of 500-millisecond conditioning hyperpolarization, the cells exhibited Ca2+-dependent action potentials. Local application to N1E-115 neuroblastoma cells of cisplatin (cis-PDD) for 30 seconds from a drug-containing effusion pipette produced a dose-dependent reversible inhibition of the Ca2+-dependent action potential, with a 61% inhibition at 1.7 microM and 67% inhibition at 17 microM cis-PDD. trans-Dichlorodiammineplatinum(II) and platinic(IV) chloride, both of which lacked the growth inhibitory properties of cis-PDD against N1E-115 neuroblastoma cells, at concentrations of 170 and 120 microM produced only an 11 and 19% inhibition of the Ca2+-dependent action potential, respectively. Vincristine at a concentration of 1 microM reversibly inhibited the Ca2+-dependent action potential by 48%. 3'-Deamino-3'-(3''-cyano-4''-morpholinyl)doxorubicin, a more potent experimental antitumor agent than doxorubicin, at 10(-8) M inhibited the Ca2+-dependent action potential by 22%, similar to the inhibition previously reported for doxorubicin. None of the agents affected the cell transmembrane potential, which suggests a lack of an effect on the mechanisms responsible for maintaining the resting cell membrane potential difference. The effects of the agents on the Ca2+-dependent action potential might reflect a direct effect on a plasma membrane Ca2+ channel or on the lipid domain around the channels, or they might be produced by changes in intracellular Ca2+ homeostasis, among other mechanisms. It is not known whether a change in the membrane Ca2+ current is related to the antitumor effects of the agents, but such a change may contribute to the neurotoxicity of cis-PDD and vincristine and the cardiac toxicity of the anthracycline.

The effects of prolonged superfusions with acidic amino acids and their agonists on field potentials and horizontal cell photoresponses in the turtle retina

The effects of prolonged superfusions with acidic amino acids and their agonists, kainic acid (KA) and N-methyl-D-aspartate (NMDA), on horizontal cells, and extracellular field potentials were studied in the turtle everted eyecup preparation using simultaneous intracellular and extracellular recordings. In a fresh preparation initial superfusions with each of the above agents usually induced a large (up to 60 mV) transient negative extracellular field potential recorded adjacent to horizontal cells, followed by a sustained negative potential of lesser amplitude (up to 10 mV). The amplitude of the sustained potential did not vary with subsequent superfusions, whereas that of the transient phase was reduced. KA and NMDA were much more potent (at least 300 times) in evoking these field potentials than either acidic amino acid. The horizontal cell transmembrane potential was monitored as the difference between the intra- and extracellular potentials. Superfusion with KA and NMDA produced a triphasic time course of the drug effect consisting of an initial depolarization with reduced photoresponses, a rehyperpolarization of the membrane accompanied by a growth of the light responses followed by a gradual depolarization and loss of photoresponses. Superfusion with the acidic amino acids usually produced a biphasic response that resembled qualitatively the first two phases of the response to KA and NMDA. This biphasic response was occasionally followed by a gradual depolarization and loss of the light response. The kinetics of the transient component of the field potential and the rapid reduction and regrowth of the photoresponses recorded during superfusion with these agents suggests an initial action of these drugs, which is of a nonsynaptic origin and which may be an expression of a drug-induced spreading depression. The kinetics of the photoresponses recorded during superfusion with KA, L-aspartate, and L-glutamate were similar but differed from those recorded during superfusion with NMDA. The difference in the effects of NMDA and KA on photoresponse kinetics suggests that two types of acidic amino acid receptors may be present in the outer plexiform layer of the turtle retina.

Transmembrane potential of renal papillary epithelial cells: effect of urea and DDAVP.

To define how renal papillary epithelial cells respond to wide changes in the ionic and osmotic composition of their environment, measurements were made of the transmembrane potential differences (PD) of rat renal papillary epithelial cells in vitro in media containing 100 mM NaCl, 100 mM KCl, 1.5 mM CaCl2, and 1 mM MgSO4 plus varying amounts of urea and/or sucrose up to 1,400 mM. Glass microelectrodes (resistance 25-75 M Omega) were used. With added sucrose, no change in PD from the initial value of -9.3 +/- 1.3 (SD) mV (n = 29) (cell interior negative) was found. With added urea, alone or while osmolality was maintained nearly constant with sucrose, the PD changed in a triphasic manner, depolarizing to -5.3 mV at 50 mM urea, hyperpolarizing to -20.0 mV at 150 mM urea, and then depolarizing again to -5.5 mV at 1,400 mM urea. When bath potassium was decreased to 10 meQ/liter (choline replacement) the PD hyperpolarized to -46.9 +/- 5.0 (SD) mV (n = 32). DDAVP, a nonpressor vasopressin analogue, and 8-bromo-cAMP depolarized the membrane to -5 mV in the presence of urea but did not change PD when urea was absent. These observations suggest an interaction between urea and ionic movement or conductance in rat renal papillary epithelial cells.

Arterial plasma potassium measured continuously during exercise in man.

Five continuous records of arterial plasma potassium were obtained from three normal subjects during brief periods (5-7 min) of exercise (100 W). In two of these subjects hepatic venous blood samples were withdrawn at 0.5-1.0 min intervals and analysed in vitro for plasma potassium. Arterial plasma potassium rose rapidly at the start of exercise from 3.8 +/- 0.3 mmol/l (mean +/- SD) to plateau levels of 5.4 +/- 0.1 mmol/l. One of the above subjects and a further subject were studied after beta-blockade with propranolol. This resulted in an exaggerated rise in arterial plasma potassium during exercise. Hepatic venous potassium measurements indicated that the liver probably had little effect on potassium changes during exercise. The changes in arterial plasma potassium during exercise are rapid and substantial. If transmitted to the extracellular fluid these changes would alter cell transmembrane potential and might as a result alter receptor sensitivity.

Relationship of muscle growth in vitro to sodium pump activity and transmembrane potential.

Serum stimulates embryonic avian skeletal muscle growth in vitro and the growth-related processes of amino acid transport and protein synthesis. Serum also stimulates myotube Na pump activity (measured as ouabain-sensitive rubidium-86 uptake) for at least 2 h after serum addition. Serum-stimulated growth depends on this Na pump activity since ouabain added at the same time as serum totally inhibits the growth responses. The relationship of myotube growth, Na pump activity, and transmembrane potential was studied to determine whether serum-stimulated Na pump activation and growth are coupled by long-term membrane hyperpolarization. When myotube amino acid transport and protein synthesis are prestimulated by serum, ouabain was found to have little inhibitory effect, indicating that the already stimulated growth-related processes are not tightly coupled to continued Na pump activity. Serum-stimulated protein synthesis is tightly coupled to Na pump activity, but only during the first 5-10 min after serum addition. When myotube transmembrane potentials were measured using the lipophilic cation tetraphenylphosphonium, serum at concentrations that stimulate myotube growth and Na pump activity was found to have little effect on the cell's transmembrane potential. Furthermore, partial depolarization of the myotubes with 12- to 55-mM extracellular potassium does not prevent serum stimulation of myotube growth. Monensin was found to hyperpolarize the myotubes, but causes myotube atrophy. These results indicate that although Na pump activity is associated with initiation of serum-stimulated myotube growth, continued Na pump activity is not essential, and there is little relationship between myotube growth and the myotube's transmembrane potential.

Changes in red blood cell transmembrane potential, electrolytes, and energy content in septic shock.

Septic shock was induced in adult baboons by the infusion of live Escherichia coli. A progressive derangement in skeletal muscle cell function was documented by the direct measurement of declining transmembrane potential difference (PD). A concurrent depolarization of the red blood cell (RBC) was characterized by cellular uptake of chloride, sodium, and water, and loss of potassium. The decrease in RBC PD was significantly greater than the change predicted to occur from acidosis alone. These findings are compatible with changes in membrane permeability and decreased active transport. The continuous accumulation of RBC adenosine triphosphate during shock suggests decreased energy utilization rather than decreased energy production as a factor leading to diminished active ion transport.

Vascular Smooth Muscle Membrane Potential and a Ouabain-Like Humoral Factor in One-Kidney, One-Clip Hypertension in Rats

1. Transmembrane potentials (Em) of vascular muscle cells in caudal arteries in vitro from one-kidney, one-clip hypertensive and one-kidney, sham-clipped normotensive rats were measured. 2. The Em recorded in hypertensive rats was significantly lower (depolarized) than that recorded in normotensive control rats. 3. Boiled plasma supernatants from hypertensive rats depolarized the muscle cells in normotensive caudal artery but had no effect on muscle cells in arteries from hypertensive rats. 4. Boiled plasma supernatants from normotensive control rats had no effect on the Em of either animal. 5. Ouabain depolarized muscle cells of the normotensive artery only and the magnitude of depolarization induced was nearly the same as that produced by the supernatant from the hypertensive animals. 6. These data suggest that a ouabain-like humoral substance may play a role in the pathophysiology of one-kidney, one-clip hypertension through a voltage-dependent mechanism.

Effects of potassium and chloride on the membrane potentials of P815 mastocytoma tumor cells.

The steady-state transmembrane potentials of P815 mastocytoma cells were recorded when the cells were bathed in salines of different compositions. In the normal growth medium (RPMI 1640 with added fetal calf serum) the mean membrane potential was -8.7 mV (SEM +/- 0.4, n = 22). A family of Tris-buffered salines (TBS), modeled from Dulbecco's modified PBS (289 mosmol, 169 milliionic strength units, pH 7.5), having different K+ and different C1- concentrations, were designed and used to bathe the tumor cells. All of the TBS solutions had constant, but reduced levels of ionized Ca2+. In the absence of external C1-, an increase of external K+ from 2 to 20 mM results in a 5.7 mV depolarization. In the presence of external C1- the same increase in external K+ results in a 2.1 mV depolarization. The presence of 145 mM C1- resulted in a steady-state depolarization (for either level of K) of about 50%. One explanation for these results would be the presence of an inward-going active C1- transport.

Membrane potentials and contractile events of hypertrophied rat cardia muscle.

AbstractPrevious studies indicate that cardiac hypertrophy is associated with altered mechanical properties including prolonged contraction times and mechanical refractory periods and exaggerated aftercontractions in isolated rat papillary muscle preparations. The present study was designed to ascertain whether changes in transmembrane potentials accompany the altered mechanical properties. Responses of papillary muscles from hypertrophied hearts of deoxycorticosterone acetate-treated Wistar Kyoto (WKY) rats were compared to those of nonhypertrophied, sham-treated WKYs. Muscles connected to a force transducer in a bathing chamber containing a 27° oxygenated physiological salt solution were subjected to field stimulation and isometric tension measured. Intracellular microelectrodes were used to measure transmembrane potentials of single impaled cells. When compared to nonhypertrophied controls, the hypertrophied preparations had (1) longer action potentials and contraction times, (2) longer electrical and ...

Molecular mechanism of acetylcholine receptor-controlled ion translocation across cell membranes.

Two molecular processes, the binding of acetylcholine to the membrane-bound acetylcholine receptor protein and the receptor-controlled flux rates of specific inorganic ions, are essential in determining the electrical membrane potential of nerve and muscle cells. The measurements reported establish the relationship between the two processes: the acetylcholine receptor-controlled transmembrane ion flux of (86)Rb(+) and the concentration of carbamoylcholine, a stable analog of acetylcholine. A 200-fold concentration range of carbamoylcholine was used. The flux was measured in the millisecond-to-minute time region by using a quench flow technique with membrane vesicles prepared from the electric organ of Electrophorus electricus in eel Ringer's solution at pH 7.0 and 1 degrees C. The technique makes possible the study of the transmembrane transport of specific ions, with variable known internal and external ion concentrations, in a system in which a determinable number of receptors is exposed to a known concentration of ligand. The response curve of ion flux to ligand was sigmoidal with an average maximum rate of 84 sec(-1). Carbamoylcholine induced inactivation of the receptor with a maximum rate of 2.7 sec(-1) and a different ligand dependence so that it was fast relative to ion flux at low ligand concentration but slow relative to ion flux at high ligand concentration. The simplest model that fits the data consists of receptor in the active and inactive states in ligand-controlled equilibria. Receptor inactivation occurs with one or two ligand molecules bound. For channel opening, two ligand molecules bound to the active state are required, and cooperativity results from the channel opening process itself. With carbamoylcholine, apparently, the equilibrium position for the channel opening step is only one-fourth open. The integrated rate equation, based on the model, predicts the time dependence of receptor-controlled ion flux over the concentration range of carbamoylcholine investigated. The values of the constants in the rate equation form the basis for predicting receptor-controlled changes in the transmembrane potential of cells and the conditions leading to transmission of signals between cells.

Alterations in the liver cell transmembrane potential following CCl 4 and bile salt treatment of rats

The liver cell transmembrane potential was measured in anesthetized, artificially ventilated rats. A 24 hour pretreatment of rats with CCl 4 produced a dose dependent depolarization from the control potential of −47.5 ± 1.2 mV (mean ± S.E.M.). A depolarization of a smaller magnitude was also observed several minutes following a treatment with taurocholate. In contrast to these alterations, taurolithocholate treatment produced a hyperpolarization in the liver cell transmembrane potential. These results suggets the liver cell membrane potential may reflect the functional integrity of the hepatocyte. The specific mechanism(s) responsible for these drug induced changes remains unknown although altered membrane permeability or altered Na +-K + pump action could play some role.

Acetylcholine receptor-controlled ion fluxes in membrane vesicles investigated by fast reaction techniques.

The ability of a nerve cell to integrate its response to chemical signals (neurotransmitters) arriving from many other cells is central to the function of the nervous system. This integration process depends on the ability of the neurotransmitters to bind to specific receptors which modulate the flow of specific inorganic ions through the cell membrane, and on the ability of the cell to transmit a (chemical) signal to an adjacent cell1–3 only if the resulting change in transmembrane potential is of appropriate sign and magnitude. The controlling sign and magnitude of the cell transmembrane potential can be predicted from measurement of the rates of movement of specific inorganic ions across the membrane4–6 and their dependence on neurotransmitter concentration. However, there have been two main obstacles to the development of a suitable preparation for such measurements. First, Kasai and Changeux7 obtained a membrane vesicle preparation from the electric organ of Electrophorus electricus (electroplax vesicles) in which acetylcholine receptor-controlled fluxes of inorganic ions could be observed, but the flux rates seemed too slow to be of physiological significance8. We have shown that these slow flux rates were associated with a large fraction of the vesicle preparation which did not respond to acetylcholine and yet dominated the measurements9. We then accomplished the separation of the receptor-controlled fluxes from other processes9,10. Second, the receptor-controlled flux was found to be biphasic, with an initial phase too fast to be measured by available techniques11. We have now succeeded in applying a quench flow technique12 to the determination of the flux rate of specific inorganic ions across vesicle membranes in the millisecond time region, a time resolution sufficient for measuring the initial phase of receptor-controlled fluxes with these vesicles.

Hypoxia independence of organ of Corti cell transmembrane potentials.

Hypoxia independence of organ of Corti cell transmembrane potentials.

Transmembrane potential measurements as an indicator of heterogeneous distribution of nutritive blood flow in skeletal muscle during shock.

AbstractThe heterogeneity of nutritive skeletal muscle blood flow during shock was studied in terms of cellular transmembrane potential variations. Shock was induced in dogs by exteriorization of the small intestine for 3 h, whereafter the intestine was replaced and the dogs were studied for another 3–4 h. Transmembrane potentials of single skeletal muscle cells were recorded by the use of modified Ling‐Gerard microelectrodes. The mean resting transmembrane potential in control animals was ‐90.4 mV ± 0.7. The variation in transmembrane potential between adjacent fibers was small. During shock there was a significant decrease in the mean transmembrane potential and at the same time there was an increasing variation of up to 29 mV in the values between adjacent fibers. To exclude metabolic differences between red and white fibers as the main reason for this increasing heterogeneity of transmembrane potentials of adjacent fibers, complete tourniquet ischemia was also studied. The total tissue ischemia resulted in a marked reduction of the transmembrane potential in all cells with only small differences between adjacent fibers. After release of the tourniquet a marked spread of resting membrane potentials, with variations of 17–25 mV between adjacent fibers, occurred. This variation was similar to that observed during shock. It is concluded that repeated transmembrane potential registrations may reveal the variable state of adjacent cells subjected to a heterogeneous nutritive blood flow in shock.

Effect of the Shoot on the Transmembrane Potentials of Root Cortical Cells of Sunflower

Transmembrane potentials (PD) of root cortical cells were measured between the vacuole and the external solution while the roots remained attached to the plants. External solution con centration was varied by using a range of dilutions of a balanced nutrient solution. In all cases the PD was more negative than that due to diffusion alone indicating the presence of an elec trogenic or metabolically derived component. This component contributed an additional —80 mV to the PD and was relatively independent of the external solution concentration. The metabolic component was eliminated by metabolic inhibitors, placing the shoot in darkness, ringing the phloem, or severing the rootlet from the shoot ; it was restored again by removing the inhibitor, by light, or, in the case of severance, by adding 25 ml sucrose to the medium. The magnitude of the electrogenic component of the PD was dependent on the antecedent light intensity in a way reminiscent of translocation itself.