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J M Dubois

Publications and source records attributed to J M Dubois.

At least 19 recordsLinked to original sources
PubMed2006

Oxaliplatin, an anticancer agent that affects both Na+ and K+ channels in frog peripheral myelinated axons.

The use of oxaliplatin, a relatively new chemotherapeutic agent, is somewhat limited since it produces a specific peripheral neuropathy regarding other neurotoxic anticancer platinum analogues. In order to investigate the mechanism of such a peripheral neuropathy, the effects of 1-100 micromol/l oxaliplatin were assessed on the nodal ionic currents of single frog myelinated axons as a model of peripheral excitable membranes. Oxaliplatin decreased both Na(+) and K(+) currents in a dose-dependent manner and within 5-10 min, without producing any marked changes in the current kinetics. It was about three to eight times more effective in reducing the Na(+) than the K(+) current. In addition, it shifted the voltage-dependence of both Na(+) and K(+) conductances towards negative membrane potentials. A negative shift in the steady-state inactivation-voltage curve of the peak Na(+) current was also observed in the presence of oxaliplatin. These effects were not reversed by washing the myelinated axons with an oxaliplatin-free solution for at least 30 min. It is concluded that oxaliplatin modifies the voltage-dependent ionic channels mainly by altering the external surface membrane potential. The knowledge of such a mechanism may help to counteract the neurotoxic action of this anticancer agent.

Animals↗
PubMed2004

Calcium-dependent proliferation of NG108-15 neuroblastoma cells.

While there is increasing evidence that Ca2+ plays an important role in regulating cell proliferation, the precise mechanisms have not been clearly elucidated so far. In order to gain insight into how Ca2+ controls cell division, the rate of proliferation, cell volume, viability and attachment to the culture support were measured in NG108-15 neuroblastoma cells in the presence of various extracellular Ca2+ concentrations ([Ca2+]o). Culture medium [Ca2+]o was decreased from 1.8 mmol/l to various values down to 1 micromol/l with EGTA. The rate of cell proliferation was almost independent of [Ca2+]o between 1.8 mmol/l and 45 micromol/l. It was decreased by about 50% at 12 umol/l Ca2+ and was almost zero in the presence of 1 micromol/l Ca2+. As we hawe shown previously (Rouzaire-Dubois and Dubois 1998) long-term hypertonicity increased the cell volume and decreased the rate of proliferation. The effects of hypertonicity and decrease in [Ca2+]o on cell proliferation were synergistic and can be described by cell size-dependent and independent mechanisms, respectively. Relative to control conditions (1.8 mmol/l Ca2+), decreases in [Ca2+]o to 12 and 1 micromol/l decreased the cell viability to 76 and 52% and the cell adhesion to dishes to 16 and 3%, respectively. Altogether, these results indicate that the effects of alteration in [Ca2+]o and cell size on neuroblastoma cell proliferation are independent and act on different signalling pathways controlling cell division.

Animals↗
PubMed2001

Background osmolyte current involved in cell volume regulation of neuroblastoma x glioma hybrid NG108-15 cells.

Recently, we showed that at constant extracellular osmolarity, the volume of NG108-15 cells was dependent on the external NaCl concentration and we assumed that the responsible mechanism was mediated by background channels (Rouzaire-Dubois et al. 1999). In order to confirm this view, the mean cell volume and the background current of NG108-15 cells were measured under different experimental conditions, after blockade of specific volume regulating mechanisms and ion channels. When the external NaCl concentration was decreased, the reversal potential of the background current was shifted toward negative values and the membrane conductance decreased. Opposite effects were observed when the NaCl concentration was increased. Substitution of external Na+ with various monovalent cations altered the mean cell volume by: Rb+, +17%; Cs+, +15%; K+, +10%; Li+, -6%; choline, -9%; N-methylglucamine, -25% . The reversal potential of the background current and the membrane conductance were altered by these Na+ substitutes in such a way that the cell volume increased linearly with the background current at -60 mV. Substitution of external Cl- with various monovalent anions altered the mean cell volume by: I-, +4%; Br-, 0%; NO-, -3%; F-, -5%; isethionate, -30%; gluconate, -50%. Cl- substitutes did not significantly alter the background current at -60 mV, except F- which increased it by 39%. These results suggest that 1. the cell volume is dependent on ion fluxes through background channels; 2. electrogenic cation fluxes are larger than anionic ones and the background current is proportional to the difference between these fluxes; 3. whereas external cations do not interfere with anion fluxes, external anions alter cation fluxes.

Anions↗
PubMed2000

Control of cell proliferation by cell volume alterations in rat C6 glioma cells.

K+ and Cl- channels are involved in regulating the proliferation of a number of cell types. Two main hypotheses have been proposed to explain the mechanism by which these channels influence cell proliferation: regulation of membrane potential and regulation of cell volume. In order to test these hypotheses, we measured, under different experimental conditions, the volume, membrane potential and rate of proliferation of C6 glioma cells. Cells cultured in control medium for 1-4 days were compared with cells cultured for the same period of time in the presence of broad spectrum channel blockers: tetraethylammonium, 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) and Cs+, in hypertonic media (29% increased osmolarity with NaCl, KCl or sucrose), in hypotonic medium (23% decreased osmolarity with H2O) or in the presence of the specific channel blockers, i.e. mast cell degranulating peptide, charybdotoxin or chlorotoxin. In all of these conditions, we observed a close correspondence between the rate of proliferation and the mean cell volume. The proliferation decreased when volume increased. Moreover, whereas control cells were flattened, spindle-shaped, bipolar or multipolar, cells cultured in media supplemented with NPPB, KCl or CsCl were round with few processes. Of the agents tested, only KCl and Cs+ depolarized the cells. These results show that alterations of the rate of proliferation by K+ and Cl- channel blockers or anisotonia are closely related with changes in cell volume or form but are not correlated with changes in membrane potential.

Animals↗
PubMed1999

Evidence for several mechanisms of volume regulation in neuroblastoma x glioma hybrid NG108-15 cells.

Volumes of neuroblastoma x glioma hybrid NG 108-15 cells were electronically measured in order to characterize the mechanisms involved in volume regulation in isosmotic and anisosmotic conditions. The cells behave as perfect osmometers when tonicity was changed at constant chloride concentration by adding sucrose or replacing NaCl with CaCl2 or MgCl2. In contrast, the cell volume was poorly dependent on tonicity when the Cl- concentration was changed by adding NaCl or H2O. Cell shrinkage was induced by cell stirring or after a hypotonicity-induced swelling. These volume decreases were abolished by caffeine but not by ryanodine or EGTA. Shrinkage was also induced by the Ca2+ ionophore ionomycin. The ionomycin-induced volume decrease was abolished by EGTA. Cell swelling induced an outwardly rectifying Cl- current which was blocked by 5-nitro-2-(3-phenylpropylamino)benzoic acid, 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid and dihydroindenyloxy-alkanoic acid. When the tonicity was reduced at constant Cl- concentration by replacing NaCl with CaCl2 or MgCl2, the volume increased and then slowly decreased towards its control value. This regulatory volume decrease was blocked by 5-nitro-2-(3-phenylpropylamino)benzoic acid, 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid and dihydroindenyl-oxy-alkanoic acid. Long-term (hours-days) cell shrinkage was induced by a reduction of the culture medium osmolarity. Long-term cell swelling was induced by an increase of the culture medium osmolarity. These volume changes were abolished by the protein translation inhibitor cycloheximide. The results suggest that NG 108-15 cell volume is regulated by at least four interacting mechanisms controlled, respectively, by intracellular Ca2+, extracellular NaCl, cell volume and intracellular ionic strength. The speculative nature of ionic systems responsible for these volume regulating mechanisms is discussed.

Animals↗
PubMed1998

K+ channel block-induced mammalian neuroblastoma cell swelling: a possible mechanism to influence proliferation.

1. A variety of studies have suggested that K+ channel activity is a key determinant for cell progression through the G1 phase of mitosis. We have previously proposed that K+ channels control the activity of cell cycle-regulating proteins via regulation of cell volume. In order to test this hypothesis, we measured, with a Coulter counter and under different experimental conditions, the volume and rate of proliferation of neuroblastoma x glioma hybrid NG108-15 cells. 2. The K+ channel blockers TEA (1-10 mM), 4-aminopyridine (0.2-2 mM) and Cs+ (2.5-10 mM) increased the cell volume and decreased the rate of cell proliferation. Proliferation was fully inhibited when cell volume was increased by 25 %. 3. A 40 % increase in the culture medium osmolarity with NaCl induced a 25 % increase in cell volume and an 82 % decrease in the rate of cell proliferation. A 40 % increase in the culture medium osmolarity with mannitol induced a 9 % increase in cell volume and a 60 % decrease in the rate of cell proliferation. 4. The Cl- channel blocker NPPB (5-nitro-2-(3-phenylpropylamino) benzoic acid; 50 microM) induced a 12 % increase in cell volume and a 77 % decrease in the rate of cell proliferation. 5. A 24 % reduction in the culture medium osmolarity with H2O induced a 21 % decrease in cell volume and a 32 % increase in the rate of cell proliferation. 6. Under whole-cell patch-clamp conditions, antibiotics (penicillin plus streptomycin) decreased the voltage-dependent K+ current. Omission of antibiotics from the culture medium induced a 10 % decrease in the cell volume and a 32 % increase in the rate of cell proliferation. 7. These results suggest that the mechanisms controlling cell proliferation are strongly influenced by the factors which determine cell volume. This could take into account the role in mitogenesis of K+ channels and of other ionic pathways involved in cell volume regulation.

4-Aminopyridine↗
PubMed1998

Alterations of ionic membrane permeabilities in multidrug-resistant neuroblastoma x glioma hybrid cells.

A population of NG108-15 neuroblastoma cells resistant to doxorubicin (NG/DOXR) was established. The cells exhibited a multidrug resistance phenotype with cross-resistance to vinblastin and colchicine, overexpression of a 170 kDa membrane protein identified as P-glycoprotein and reversal of resistance by verapamil and quinine. Compared with NG108-15 cells, NG/DOXR cells showed an increase in Na+ current density and a decrease in cyclic-AMP-activated Cl- current density with no change in K+- and volume-sensitive Cl- current densities. As previously observed in NG108-15 cells, the vacuolar-type H+-ATPase inhibitors bafilomycin A1 and nitrate induced membrane depolarizations in NG/DOXR cells. The resting potentials of sensitive and resistant cells were not significantly different, but the depolarizations evoked by these agents were significantly larger in NG/DOXR than in NG108-15 cells. The resting membrane potential of NG/DOXR cells, but not that of NG108-15 cells, was depolarized by verapamil, and this effect was abolished by bafilomycin. The volume-sensitive Cl- currents of drug-sensitive and drug-resistant cells were inhibited by a decrease in intracellular pH from 7.3 to 6.8. Whereas bafilomycin prevents activation of Cl- currents in both drug-sensitive and drug-resistant cells, verapamil inhibited the Cl- current only in NG/DOXR cells. The results are discussed in terms of the roles of cytoplasmic pH and membrane potential in multidrug resistance.

Animals↗
PubMed1997

A proton pump contributes to neuroblastoma x glioma cell membrane potentials.

The contribution of an electrogenic proton pump to the membrane potential of neuroblastoma x glioma hybrid NG 108-15 cells was determined with whole-cell voltage and current recordings and cell volume measurements with the preparation bathed in symmetrical 140 mM KCl solutions. The effects of the K+ channel blockers tetraethylammonium and 4-aminopyridine and of the H+-ATPase inhibitor bafilomycin A1 on the membrane potential and input resistance revealed that the membrane potential is generated by an outward H+ pump current of 5-15 pA in equilibrium with an inward passive current. This conclusion is supported by both current- and voltage-clamp results obtained when the preparation was bathed in a Na+-containing external solution after K+ channel blockade with Cs+ in the pipette. Additional support was obtained by measurement of the volume of cells incubated in solutions containing 140 mM KCl. Tetraethylammonium induced a bafilomycin-sensitive increase in inward K+ current and an increase in cell volume of 76% which we believe to be a consequence of the K+ influx. Finally, comparison of membrane potentials obtained in experiments using Na+-containing external, and K+-containing pipette solutions and after K+ channel blockade with Cs+ in the pipette also showed that, under normal physiological conditions, the resting membrane potential is essentially determined by an electrogenic H+ pump.

Cell Membrane↗
PubMed1997

Prone position in mechanically ventilated patients with severe acute respiratory failure.

The purpose of this study was to characterize changes in oxygenation, expressed as PaO2/F(I)O2, when patients with severe acute respiratory failure (PaO2/F(I)O2 < 150), unrelated to left ventricular failure to atelectasis, were turned to and from a supine to prone position at 1- and 4-h intervals. Ventilator settings were unchanged. Thirty-two consecutive patients were studied 1 h before, 1 and 4 h during and 1 h after placing in a prone position with PaO2/F(I)O2 of 103 +/- 28, 158 +/- 62, 159 +/- 59, and 128 +/- 52, respectively (ANOVA, p < 0.001). After 1 h in a prone position, improvement of PaO2/F(I)O2 by 20 mm Hg or more was considered a positive response. Seven patients studied had no response (22%), hereafter referred to as nonresponders, and 25 had a positive response (78%), hereafter referred to as responders. Among the seven nonresponders, two did not tolerate the prone position and were returned supine before the end of the 4-h trial. With the remaining five, PaO2/F(I)O2 evolution was 83 +/- 29, 77 +/- 19, 83 +/- 33, and 81 +/- 47, respectively. For two of the 25 responders, measurements are missing after returning to the supine position. In 10 of the 23 responders (43%) who completed the 4 h prone trial, the PaO2/F(I)O2 returned to its starting value when patients were repositioned supine: 117 +/- 24, 164 +/- 44, 156 +/- 55, and 110 +/- 34, respectively (ANOVA, p < 0.01). In 13 of the 23 (57%) improvement persisted: 105 +/- 27, 187 +/- 58, 189 +/- 49, and 157 +/- 49, respectively (ANOVA, p < 0.001). Repeated improvements after turning to a prone position were frequently observed. Side effects in the 32 patients after a total of 294 periods in a prone position included minor skin injury and edema, two instances of apical atelectasis, one catheter removal, one catheter compression, one extubation, and one transient supraventricular tachycardia.

Adolescent↗
PubMed1995

Music improves patient comfort level during outpatient bronchoscopy.

STUDY OBJECTIVE: To determine the effect of music during bronchoscopy on patient perception of the procedure. DESIGN: Prospective randomized trial. SETTING: University-based bronchoscopy suite. PATIENTS: Twenty-one patients received music (M+), and 28 patients served as controls (M-). MEASUREMENTS AND RESULTS: Physiologic responses, subjective patient perceptions, and administered medications were monitored. After the procedure, the technician and the physician both rated their impression of the patients' comfort levels to see how accurately they correlated with actual patient reports. There was no difference in physiologic responses between the M+ and M- groups. The M+ patients reported significantly greater comfort (p = 0.02) and less cough (p = 0.03) than the M- group, while there was no difference in reported dyspnea P = 0.21). Both physicians and technicians were very inaccurate in their assessments of patient level of comfort. Medications given did not differ for the two groups. CONCLUSION: Music during bronchoscopy is a simple and inexpensive nonpharmacologic way to improve patient comfort.

Adult↗
PubMed1994

Contribution of a H+ pump in determining the resting potential of neuroblastoma cells.

The aim of this work was to examine the effects of changes in external K+ concentration (Ko) around its physiological value, of various K+ channels blockers, including internal Cs+, of vacuolar H(+)-ATPase inhibitors and of the protonophore CCCP on the resting potential and the voltage-dependent K+ current of differentiated neuroblastoma x glioma hybrid NG108-15 cells using the whole-cell patch-clamp technique. The results are as follows: (i) under standard conditions (Ko = 5 mM) the membrane potential was -60 +/- 1 mV. It was unchanged when Ko was decreased to 1 mM and was depolarized by 4 +/- 1 mV when Ko was increased to 10 mM. (ii) Internal Cs+ depolarized the membrane by 21 +/- 3 mV. (iii) The internal application of the vacuolar H(+)-ATPase inhibitors N-ethylmaleimide (NEM), NO3- and bafilomycin A1 (BFA) depolarized the membrane by 15 +/- 2, 18 +/- 2 and 16 +/- 2 mV, respectively. (iv) When NEM or BFA were added to the internal medium containing Cs+, the membrane was depolarized by 45 +/- 1 and 42 +/- 2 mV, respectively. (v) The external application of CCCP induced a transient depolarization followed by a prolonged hyperpolarization. This hyperpolarization was absent in BFA-treated cells. The voltage-dependent K+ current was increased at negative voltages and decreased at positive voltages by NEM, BFA and CCCP. Taken together, these results suggest that under physiological conditions, the resting potential of NG108-15 neuroblastoma cells is maintained at negative values by both voltage-dependent K+ channels and an electrogenic vacuolar type H(+)-ATPase.

Animals↗
PubMed1994

Respiratory care practitioners' attitudes toward patients with AIDS.

OBJECTIVE: To assess attitudes of respiratory care practitioners about AIDS and patients with AIDS. DESIGN: A questionnaire that explored attitudes about AIDS was disseminated throughout southern New Jersey. Identity of individual responders was protected carefully. RESULTS: One hundred fifty-nine responses were received. The majority of responders favored identification of patients with AIDS, segregation of those patients into AIDS wards, and then avoidance of the AIDS wards. There was some bias against patients with known high-risk behaviors (especially drug abuse), but once a patient had AIDS the fear of getting AIDS was the only factor that correlated (p = 0.001) with the desire to avoid AIDS patients. Thirty-nine percent of responders said that they used universal precautions less than 90 percent of the time, and no factor (including fear of AIDS and markers of education) predicted which therapists did not consistently use them. CONCLUSIONS: The desire to avoid AIDS represents a rational desire not to become infected with the HIV virus. This study documents an identify-and-avoid philosophy in lieu of careful use of universal precautions. Educational efforts need to emphasize that the use of precautions represents the only truly effective means of preventing infection with the AIDS virus and other communicable diseases.

Acquired Immunodeficiency Syndrome↗
PubMed1993

Involvement of K+ channels in the quercetin-induced inhibition of neuroblastoma cell growth.

The effects of the flavonoid quercetin on cell proliferation and voltage-dependent K+ current were studied on mouse neuroblastoma x glioma hybrid cells. In the presence of 1% fetal calf serum, quercetin inhibited both cell proliferation and K+ current with effective doses inducing half-maximum effects of 10 microM and 70 microM respectively. Valinomycin (1 nM) antagonized 80% of the growth-inhibitory effects of 10 microM quercetin. The results suggest that at least a part of the anti-proliferative effect of quercetin is mediated by a K+ channel blockade. They further confirm a role for K+ channels in mitogenesis and cell proliferation.

Adenosine Triphosphate↗
PubMed1991

Modification of K+ channel properties induced by fatty acids in neuroblastoma cells.

The effects of fatty acids on voltage-dependent potassium (K+) channels in neuroblastoma cells were studied using the whole-cell current recording technique. At a concentration of 5 microM, unsaturated and medium chain length (C10-C14) saturated fatty acids accelerated the apparent inactivation of the K+ current. This effect was reversed by albumin. In the absence of exogenous fatty acids, albumin slowed the inactivation of the K+ current. The acceleration of the K+ current inactivation induced by unsaturated fatty acids was associated with an increase in the sensitivity of K+ channels to 4-amino-pyridine. It is concluded that kinetic and pharmacological properties of K+ channels are, in part, controlled by membrane fatty acids which, in this way, should contribute to an apparent diversity of K+ channels and the modulation of cell excitability.

Albumins↗
PubMed1991

Interaction of 4-aminopyridine with normal and chloramine-T-modified K channels of neuroblastoma cells.

The steady-state effects and rate of action of 4-aminopyridine (4-AP) on normal and chloramine-T (CL-T)-modified voltage-dependent potassium (K) currents were studied in neuroblastoma cells with the whole-cell voltage-clamp current recording technique. 4-AP apparently slows both the activation and inactivation of the normal current but does not modify the time course of the CL-T-modified current. These differential effects of 4-AP are interpreted as resulting from the existence of two types of K channels with different 4-AP sensitivities under normal conditions and similar 4-AP sensitivities after CL-T, which furthermore slows their inactivation [8, 9]. While the onset of 4-AP action on the normal current is delayed and can be described by the difference of two exponentials, the onset of 4-AP action on CL-T-modified current starts immediately after the external application of the drug and can be described by the sum of two exponentials. The 4-AP-induced block of the normal current exhibits use-dependent features and is relieved by long conditioning depolarizations. In contrast, the block of the CL-T-modified current is not use-dependent. At high 4-AP concentrations (1-10 mM), the steady-state block of the normal current reaches a saturating value of 95%, while the steady-state block of the CL-T-modified current and the "unblocked" normal current only reaches a saturating value of 35%. The results suggest that CL-T inhibits a channel or membrane constituent which contributes to the inactivation of channels and increases their apparent affinity for 4-AP when they are in closed or open states.(ABSTRACT TRUNCATED AT 250 WORDS)

4-Aminopyridine↗
PubMed1991

A quantitative analysis of the role of K+ channels in mitogenesis of neuroblastoma cells.

The role of K+ channels in mitogenesis was studied on mouse neuroblastoma cells by analysing the effects of various chemical agents on the whole-cell K+ current and the cell proliferation. The outward current recorded during depolarizations on undifferentiated cells was made up of a small and slow inactivating K+ current. Foetal calf serum, which is mitogen for neuroblastoma cells, shifted in opposite directions by 7-10 mV peak activation and steady-state inactivation-voltage curves of the K+ current. The resulting effect was an increase in K+ conductance. The effect on the resting K+ flux of the classical K+ channel blockers tetraethylammonium, 4-aminopyridine and capsaicin, the anticancer agent tamoxifen, the heat inactivated serum and the increase in external K+ concentration were estimated from their effects on the K+ current. The cell proliferation was determined under the same conditions. The results indicate that cell proliferation is correlated to the resulting K+ flux. It is supposed that mitogenesis is controlled by the intracellular Na+ concentration which, via a cell volume regulation, is a function of the K+ flux. A quantitative model is developed on the basis of these hypotheses.

Cell Division↗