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S Breton

Publications and source records attributed to S Breton.

50 records · Page 3Linked to original sources
PubMed1995

Depletion of intercalated cells from collecting ducts of carbonic anhydrase II-deficient (CAR2 null) mice.

The kidneys of mice (CAR2-null mice) that are genetically devoid of carbonic anhydrase type II (CAII) were screened by immunocytochemistry with antibodies that distinguish intercalated and principal cells. Immunofluorescent localization of the anion exchanger AE1 and of the 56-kDa subunit of the vacuolar H(+)-adenosinetriphosphatase (H(+)-ATPase) was used to identify intercalated cells, while the AQP2 water channel was used as a specific marker for principal cells of the collecting duct. The CAII deficiency of the CAR2-null mice was first confirmed by the absence of immunofluorescent staining of kidney sections exposed to an anti-CAII antibody. Cells positive for AE1 and H(+)-ATPase were common in all collecting duct regions in normal mice but were virtually absent from the inner stripe of the outer medulla and the inner medulla of CAR2-null mice. The number of positive cells was also reduced threefold in the cortical collecting duct of CAR2-null animals compared with normal mice. In parallel, the percentage of AQP2-positive cells was correspondingly increased in the collecting tubules of CAII-deficient mice, whereas the total number of cells per tubule remained unchanged. These results suggest that intercalated cells are severely depleted and are replaced by principal cells in CAII-deficient mice. Quantitative analysis and double staining showed that, in the cortex, both type A and type B intercalated cells are equally affected. Elucidation of the mechanism(s) responsible for this phenotype will be of importance in understanding the origin and development of intercalated cells in the kidney.

Animals↗
PubMed1994

cAMP stimulates proximal convoluted tubule Na(+)-K(+)-ATPase activity.

The effect of adenosine 3',5'-cyclic monophosphate (cAMP) was examined on the electrophysiological properties of nonperfused proximal convoluted tubule in vitro. In 5 mM bath K+, the basolateral membrane potential (Vbl) was -66 +/- 1 mV (n = 26). Low bath K+ (0.1 mM) led to a transient hyperpolarization of Vbl followed by a sustained decrease to reach -48.6 +/- 5.0 mV. Return to 5 mM bath K+ produced a rapid and transient Vbl hyperpolarization of 24.6 +/- 1.4 mV (n = 5). This hyperpolarization was completely blocked by 100 microM strophanthidin (n = 4), demonstrating that the hyperpolarization was caused by reactivation of the Na(+)-K(+)-adenosinetriphosphatase (ATPase). Addition of 1 microM forskolin (forsk) + 100 microM 8-(4-chlorophenylthio)-cAMP (cp-cAMP) significantly increased this hyperpolarization to 30.8 +/- 10 mV (P < 0.005, n = 5). In a separate series of experiments, addition of 1 microM forsk + 100 microM 3-isobutyl-1-methylxanthine increased this hyperpolarization from 21.7 +/- 2.8 to 27.1 +/- 1.6 mV (P < 0.05, n = 5), which excludes any nonspecific effect of cp-cAMP. Forsk + cp-cAMP decreased the apparent partial conductance to Cl- (tCl) from 0.049 +/- 0.003 to 0.031 +/- 0.007 (P < 0.06, n = 6), decreased that to K+ (tK) from 0.56 +/- 0.05 to 0.43 +/- 0.03 (P < 0.05, n = 6), slightly decreased that mediated by the Na-HCO3 cotransporter (tNaHCO3) from 0.26 +/- 0.03 to 0.21 +/- 0.05, and had no effect on the absolute conductance mediated by the Na-HCO3 cotransporter. Forsk + cp-cAMP had no effect on tK when determined using bath K+ steps from 15 to 45 mM (tK = 0.84 +/- 0.02, n = 5) instead of K+ steps from 5 to 15 mM as previously done, and did not affect the value of tK measured in the presence of strophanthidin (tK = 0.41 +/- 0.03, n = 5). These results demonstrate that the decrease of tK by forsk + cp-cAMP observed using K+ steps from 5 to 15 mM is due to modulation by these agents of the stimulated hyperpolarizing Na(+)-K(+)-ATPase current produced by the bath K+ steps. Consequently, the increased Vbl initial recovery from low bath potassium observed when intracellular cAMP is increased could not be the result of modulation of passive basolateral membrane properties and represents a stimulation of the pump current. The present work thus demonstrates that the Na(+)-K(+)-ATPase is stimulated by cAMP.

Animals↗
PubMed1993

Basolateral K+, Cl-, and HCO3- conductances and cell volume regulation in rabbit PCT.

The relationship between changes in cellular volume, intracellular pH (pHi), basolateral membrane potential (VBL), and membrane partial basolateral conductances to K+ (tK) and Cl- (tCl) and mediated by the Na-HCO3 cotransporter (tNaHCO3) was determined in the collapsed proximal convoluted tubule (PCT) submitted to a 125-mosmol/kg hypotonic shock. The shock that produces a rapid swelling followed by partial volume regulation was accompanied by a rapid and transient VBL hyperpolarization of 10.0 +/- 1.5 mV and a second gradual hyperpolarization of 5.0 +/- 0.7 mV with respect to a control value of -44.0 +/- 4.6 mV.tK was 0.12 +/- 0.03 in control, increased transiently to 0.15 +/- 0.03, and then gradually increased to reach 0.32 +/- 0.06 at the end of hypotonic shock. In contrast, tCl was 0.03 +/- 0.01 in control, increased rapidly to a maximum of 0.16 +/- 0.01, and then decreased slowly to 0.08 +/- 0.02. During the same period, tNaHCO3 decreased rapidly from 0.41 +/- 0.04 to a minimum of 0.11 +/- 0.02 and slowly reincreased to reach 0.16 +/- 0.01.pHi increased transiently from 7.09 +/- 0.03 in control to 7.24 +/- 0.05 to come back gradually to 7.15 +/- 0.05 at the end of the hypotonic period. The membrane absolute conductance mediated by the Na-HCO3 cotransporter was found to increase only slightly in hypotonic conditions, whereas that to K+ and Cl-, GK and GCl, increased by at least factors of 8 and 17, respectively, with the increase of GCl being much faster than that of GK. In addition, the temporal variations in GCl followed closely those of the cellular water efflux. We conclude that the hypotonic swelling leads to important increases in the conductive pathways for K+ and Cl- and that the Cl- conductance pathway appears to be the rate limiting step in triggering and supporting regulatory volume decrease.

Animals↗
PubMed1992

pH-dependent heterogeneity of acidic amino acid transport in rabbit jejunal brush border membrane vesicles.

Initial rates of Na(+)-dependent L-glutamic and D-aspartic acid uptake were determined at various substrate concentrations using a fast sampling, rapid filtration apparatus, and the resulting data were analyzed by nonlinear computer fitting to various transport models. At pH 6.0, L-glutamic acid transport was best accounted for by the presence of both high (Km = 61 microM) and low (Km = 7.0 mM) affinity pathways, whereas D-aspartic acid transport was restricted to a single high affinity route (Km = 80 microM). Excess D-aspartic acid and L-phenylalanine served to isolate L-glutamic acid flux through the remaining low and high affinity systems, respectively. Inhibition studies of other amino acids and analogs allowed us to identify the high affinity pathway as the X-AG system and the low affinity one as the intestinal NBB system. The pH dependences of the high and low affinity pathways of L-glutamic acid transport also allowed us to establish some relationship between the NBB and the more classical ASC system. Finally, these studies also revealed a heterotropic activation of the intestinal X-AG transport system by all neutral amino acids but glycine through an apparent activation of Vmax.

Amino Acids↗
PubMed1992

Potassium conductance regulation by pH during volume regulation in rabbit proximal convoluted tubules.

When rabbit proximal convoluted tubules were microperfused in the presence of bicarbonate, a 90 mosmol hypotonic shock hyperpolarized the basolateral membrane by 5.5 +/- 1.4 mV, increased basolateral potassium selectivity (tK) from 0.30 +/- 0.02 to 0.45 +/- 0.02, and reduced the basolateral membrane resistance from 4,887 +/- 821 to 2,836 +/- 602 omega.cm. These data show that the hypotonic shock increased absolute basolateral potassium conductance. The same hypotonic shock elevated intracellular pH from 7.18 +/- 0.04 to 7.31 +/- 0.04. When bath pH was increased by 0.2 pH units (by reduction of CO2), intracellular pH rose by 0.13 +/- 0.01. In separate experiments this maneuver hyperpolarized the basolateral membrane by 5.0 +/- 0.8 mV and augmented basolateral tK from 0.58 +/- 0.06 to 0.68 +/- 0.04, suggesting that the basolateral potassium conductance is sensitive to pH changes of a magnitude similar to that evoked by a hypotonic shock. In the nominal absence of bicarbonate or presence of 0.5 mM 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) in the bath, the hypotonic shock caused a transient intracellular acidification, suggesting involvement of basolateral bicarbonate transport in the hypotonic shock-induced alkalinization. In the absence of bicarbonate, the hypotonic shock did not increase basolateral tK or induce hyperpolarization of the basolateral membrane. We conclude that the increase in potassium conductance observed during hypotonic shock is at least partly mediated by a bicarbonate-dependent, SITS-sensitive intracellular alkalinization.

Alkalosis↗
PubMed1992

Involvement and source of calcium in volume regulatory decrease of collapsed proximal convoluted tubule.

We examined the role of Ca2+ in the volume regulatory decrease (VRD) of rabbit collapsed proximal tubules. Reduction of bath osmolality by 125 mosmol/kgH2O led to an initial cell swelling of 62.3 +/- 7.5% followed by a partial regulatory phase bringing cell volume to a value of 13.3 +/- 2.9% above control (n = 5). This swelling was accompanied by a transient intracellular Ca2+ ([Ca2+]i) increase from 174 +/- 33 to 306 +/- 67 nM (P < 0.05, n = 8). In the same condition, but in absence of extracellular Ca2+ ([Ca2+]e) [1 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA)], VRD following hypotonic shock was identical to that observed in presence of [Ca2+]e (n = 5), and [Ca2+]i increased transiently from 136 +/- 29 to 161 +/- 31 nM (P < 0.05, n = 5). Addition of 100 microM 8-(N,N-dimethylamino)octyl 3,4,5-trimethoxybenzoate hydrochloride (TMB-8), an agent known to inhibit Ca2+ release from intracellular stores, did not affect the initial cell swelling (63.4 +/- 4.2%), and VRD occurred to the same extent (25.0 +/- 7.1%, n = 4), although at a lower rate. In these conditions, [Ca2+]i, which was 113 +/- 30 nM in the isotonic solution, decreased progressively to 81 +/- 20 nM over the 5-min hypotonic period (n = 5). Mere preincubation with 100 microM TMB-8 before hypotonic shock led to a VRD identical to that observed in presence of Ca2+ and absence of TMB-8 while still blocking the Ca2+ release, with cell Ca2+ decreasing progressively from 179 +/- 32 to 87 +/- 21 nM (n = 7).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Fast sampling, rapid filtration apparatus: principal characteristics and validation from studies of D-glucose transport in human jejunal brush-border membrane vesicles.

Kinetic data in (brush-border) membrane vesicles which rely on the validity of the initial rate assumption for their interpretation and depend on tracer flux studies using the rapid filtration technique for their experimental measurement have been limited to some extent by the absence of techniques that would allow for real-time data analysis. In this paper, we report on our successful design of a fast sampling, rapid filtration apparatus (FSRFA) which seems to fill up this technical gap since showing the following characteristics: (i) rapid injection (5 msec) and mixing (less than 100 msec) of small amounts of vesicles (10-40 microliters) with an incubation medium (0.2-1.0 ml); (ii) fast (20 to 80 msec depending on the sample volume) and multiple (up to 18 samples at a maximal rate of 4 sec) sampling of the uptake mixture followed by rapid quenching in the stop solution (approximately 5 msec) according to a predetermined time schedule (any time combination from 0.25 to 9999 sec); and (iii) fast, automated, and sampling-synchronized filtration and washings of the quenched uptake medium (only 15-20 sec are necessary for the first filtration followed by two washings and extra filtrations). As demonstrated using adult human jejunal brush-border membrane vesicles and Na(+)-D-glucose cotransport as models, the FSRFA accurately reproduces the manual aspects of the rapid filtration technique while allowing for very precise initial rate determinations. Moreover, the FSRFA has also been designed to provide as much versatility as possible and, in its present version, allows for a very precise control of the incubation temperature and also permits a few efflux protocols to be performed. Finally, its modular design, which separates the fast sampling unit from the rapid filtration device, should help in extending its use to fields other than transport measurement.

Biological Transport↗
PubMed1991

Intracellular potassium activity in mammalian proximal tubule: effect of perturbations in transepithelial sodium transport.

Intracellular potassium activity (alpha Ki) was measured in control conditions in mid-cortical rabbit proximal convoluted tubule using two methods: (i) by determination of the K+ equilibrium potential (EK) using Ba(2+)-induced variations in the basolateral membrane potential (VBL) during transepithelial current injections and (ii) with double-barrel K-selective microelectrodes. Using the first method, the mean VBL was -48.5 +/- 3.2 mV (n = 16) and the mean EK was -78.4 +/- 4.1 mV corresponding to alpha Ki of 68.7 mM. With K-selective microelectrodes, VBL was -36.6 +/- 1.1 mV (n = 19), EK was -64.0 +/- 1.1 mV and alpha Ki averaged 40.6 +/- 1.7 mM. While these last EK and VBL values are significantly lower than the corresponding values obtained with the first method (P less than 0.001 and P less than 0.01, respectively), the electrochemical driving force for K transport across the basolateral membrane (microK = VBL-EK) is not significantly different for both techniques (30.1 +/- 3.3 mV for the first technique and 27.6 +/- 1.8 mV for ion-selective electrodes). This suggests an adequate functioning of the selective barrel but an underestimation of VBL by the reference barrel of the double-barrel microelectrode. Such double-barrel microelectrodes were used to measure temporal changes in alpha Ki and microK in different experimental conditions where Na reabsorption rate (JNa) was reduced. alpha Ki was shown to increase by 12.2 +/- 2.7 (n = 5) and 14.1 +/- 4.4 mM (n = 5), respectively, when JNa was reduced by omitting in the luminal perfusate: (i) 5.5 mM glucose and 6 mM alanine and (ii) glucose, alanine, other Na-cotransported solutes and 110 mM Na. In terms of the electrochemical driving force for K exit across the basolateral membrane, microK, a decrease of 5.4 +/- 2.0 mV (P less than 0.05, n = 5) was measured when glucose and alanine were omitted in the luminal perfusate while microK remained unchanged when JNa was more severely reduced (mean change = -1.7 +/- 2.1 mV, NS, n = 5). In the latter case, this means that the electrochemical driving force for K efflux across the basolateral membrane has not changed while both the active influx through the Na-K pump and the passive efflux in steady state are certainly reduced. If the main pathway for K transport is through the basolateral K conductance, this implies that this conductance must have decreased in the same proportion as that of the reduction in the Na-K pump activity.

Alanine↗
PubMed1991

Volume regulation and intracellular calcium in the rabbit proximal convoluted tubule.

The hypothesis that an increase of calcium leads to activation of calcium-activated ionic conductances during cell swelling was examined in the isolated perfused proximal convoluted tubule of the rabbit. Reduction of bath and luminal osmolality by 90 mosmol/kgH2O caused the cells to swell by 23.6 +/- 1.5% (n = 5) and intracellular calcium to rise from 227 +/- 35 to 347 +/- 60 nM (n = 6). Both these increases were transient, with volume decreasing to 5.5 +/- 1.2% above control and intracellular calcium concentration decreasing to 272 +/- 46 nM after 5-9 min. The addition of glucose and alanine to the tubule lumen to increase transcellular sodium transport caused a sustained increase in cell volume of 15.6 +/- 3.4% (n = 4). In parallel experiments, no significant increase in intracellular calcium concentration was observed. Addition of 1 microM of the calcium ionophore, ionomycin, reversibly increased intracellular calcium by 224 +/- 60 nM from a control value of 301 +/- 29 nM (n = 7) and reversibly depolarized the basolateral membrane by 3.6 +/- 0.9 mV (n = 5). However, there was no initial increase in the apparent transference number for potassium or chloride and no significant change in cell volume. We conclude from these observations that the sustained increase in basolateral potassium conductance observed when cells are swollen by hypotonicity or increased sodium transport (J. S. Beck and D. J. Potts. J. Physiol. Lond. 425: 369-378, 1990) is not due to a calcium-activated potassium conductance.

Alanine↗
PubMed1991

Relationship between sodium transport and intracellular ATP in isolated perfused rabbit proximal convoluted tubule.

The effect of alterations in sodium transport on cell ATP content and pH in the isolated perfused proximal convoluted tubule (PCT) of the rabbit was examined. Stimulating sodium transport by the addition of luminal glucose and alanine decreased cell ATP from 4.44 +/- 0.93 to 2.69 +/- 0.62 mM (n = 4), increased intracellular pH by 0.13 +/- 0.02 (n = 7), and increased cell volume by 0.10 +/- 0.02 nl/mm (n = 4). Blocking the sodium pump with 10(-4) M strophanthidin in tubules in which sodium transport had been stimulated increased cell ATP from 2.04 +/- 0.24 to 2.42 +/- 0.32 mM (n = 6). In parallel experiments the same dose of strophanthidin depolarized the basolateral membrane from -52.6 +/- 1.9 to -6.4 +/- 1.6 mV, depolarized the transepithelial potential from -3.2 +/- 0.3 to -0.1 +/- 0.1 mV, and reduced the basolateral membrane potassium transference number from 0.47 to 0.26 indicating a reduction in basolateral potassium conductance. Since strophanthidin caused a cell alkalinization of 0.15 +/- 0.03, this latter effect cannot be due to changes of intracellular pH. Strophanthidin caused no change in cell volume over the period studied, suggesting that stretch-activated potassium channels are not involved either. Instead, potassium conductance inhibition may be the result of the closure of ATP-sensitive potassium channels. These same channels might thus be partly responsible for the increase in potassium conductance commonly observed during stimulation of sodium transport.

Adenosine Triphosphate↗
PubMed1975

Hospital management of patients and personnel exposed to communicable diseases.

Patients and personnel who are exposed to certain communicable diseases in a hospital setting often require therapeutic or epidemic control measures which may differ from measures employed following community exposure. This paper offers guidelines for reducing the hospital spread of communicable diseases by preventive measures (admission screening procedures, immunizations for personnel), and post-exposure management of patients and personnel. It is intended as a companion to the "Hospital Isolation and Precaution Guidelines" for patients with clinically manifest infections which appeared previously.

Child↗
PubMedDate not supplied

Dibutyryl cyclic adenosine monophosphate stimulates the sodium pump in rabbit renal cortical tubules.

The elevation in oxygen consumption (QO2) observed following addition of the sodium ionophore nystatin in suspensions of rabbit renal proximal tubules was significantly increased by 1 mM dibutyryl cyclic adenosine monophosphate (db-cAMP). The QO2 after subsequent addition of strophanthidin to block the sodium pump was unaffected by db-cAMP. However, 10 microM forskolin in the presence of 100 microM IBMX had no significant effect on the QO2 observed following addition of either nystatin or strophanthidin. Nevertheless, we can conclude that db-cAMP does stimulate the sodium pump activity independently of sodium transport mechanisms in the rabbit renal proximal tubule.

1-Methyl-3-isobutylxanthine↗