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J R Chaillet

Publications and source records attributed to J R Chaillet.

25 records · Page 2Linked to original sources
PubMed1990

Drosophila homolog of the mammalian jun oncogene is expressed during embryonic development and activates transcription in mammalian cells.

By means of low-stringency cross-species hybridization to Southern DNA blots, human c-jun sequences were used to identify a unique Drosophila melanogaster locus (Djun). The predicted DJun protein is highly homologous to members of the mammalian Jun family in both the DNA binding and leucine zipper regions. Djun was mapped by in situ hybridization to position 46E of the second chromosome. It encodes a 1.7-kilobase transcript constitutively expressed at all developmental stages. Functionally, Djun in cooperation with mouse c-fos can trans-activate activator protein 1 DNA binding site when introduced into mammalian cells. Taken together, these data suggest that Djun, much like its mammalian homolog, may activate transcription of genes involved in regulation of cell growth, differentiation, and development. Furthermore, the identification of Djun allows one to exploit the genetics of Drosophila to identify genes in signal transduction pathways involving Djun and thus c-jun.

Amino Acid Sequence↗
PubMed1988

Intracellular pH regulation in the S3 segment of the rabbit proximal tubule in HCO3- -free solutions.

We used the absorbance spectrum of 4',5'-dimethyl-5-(and 6) carboxyfluorescein to measure intracellular pH (pHi) in the isolated, perfused S3 segment of the rabbit proximal tubule. Experiments were conducted in HCO3- -free solutions. pHi recovered from an acid load imposed by an NH4+ prepulse, indicating the presence of one or more active acid-extrusion mechanisms. Removal of Na+ from bath and lumen caused pHi to decrease by approximately 0.6, whereas Na+ readdition caused complete pHi recovery. Removal of Na+ from the bath caused only a slow pHi decrease that was enhanced about fourfold when Na+ was subsequently removed from the lumen also. Similarly, the pHi recovery produced by the readdition of Na+ to the bath and lumen was about ninefold faster than when Na+ was returned to the bath only. Amiloride (1-2 mM) inhibited the pHi recovery that was elicited by returning 15 or 29 mM Na+ to lumen by only approximately 30%. However, in the absence of external acetate (Ac-), 1 mM amiloride inhibited approximately 66% of the pHi recovery induced by the readdition of 29 mM Na+ to the lumen only. The removal of external Ac- reduced the pHi recovery rate from an NH4+-induced acid load by approximately 47%, and that elicited by Na+ readdition, by approximately 67%. Finally, when bilateral removal of Na+ was maintained for several minutes, pHi recovered from the initial acidification, slowly at first, and then more rapidly, eventually reaching a pHi approximately 0.1 higher than the initial one. This Na+-independent pHi recovery was not significantly affected by lowering [HEPES]o from 32 to 3 mM or by adding N'N'-dicyclohexylcarbodiimide (10(-4) M) to the lumen, but it was reduced approximately 57% by iodoacetate (0.5 mM) plus cyanide (1 mM). We conclude that in the nominal absence of HCO3-, three transport systems contribute to acid extrusion by S3 cells: (a) a Na+-independent mechanism, possibly an H+ pump; (b) a Na-H exchanger, confined primarily to the luminal membrane; and (c) an Ac- and luminal Na+-dependent mechanism. The contribution of these three mechanisms to total acid extrusion, assessed by the rapid readdition of Na+, was approximately 13, approximately 30, and approximately 57%, respectively.

Ammonia↗
PubMed1986

Optical measurements of intracellular pH in single LLC-PK1 cells: demonstration of Cl-HCO3 exchange.

An optical method was used to continuously monitor intracellular pH (pHi) in single cultured LLC-PK1 cells. Rapidly growing or quiescent cells, attached to coverslips, were loaded with the pH-sensitive dye 4',5'-dimethyl-5(and -6)-carboxyfluorescein by exposing them to the dye's permeant precursor. pHi was calculated from the intracellular absorbance spectrum of the dye in a single cell. For cells incubated in HCO3(-)-free Ringer's solution, pHi recovered exponentially from acid loads applied by NH+4 prepulsing. Because the recovery was Na+-dependent and amiloride-sensitive, it was probably caused by Na-H exchange at the plasma membrane. In HCO3- Ringer's solution, external Cl- removal caused pHi to reversibly increase by approximately equal to 0.3. This pHi increase was substantially reduced by 50 microM 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS) or by conducting the Cl- removal in the nominal absence of HCO3-. Reducing [HCO3-]o from 25 to 5 mM at constant pCO2 (lowering pHo from 7.4 to 6.7) caused pHi to reversibly fall by approximately equal to 0.2. This pHi change was greatly diminished by DIDS, by removal of extracellular Cl-, or by performing the same pHo shift in the nominal absence of HCO3-. The pHi changes induced by altering [Cl-]o or pHo were not inhibited by Na+ removal. Our data indicate that LLC-PK1 cells possess a Na-independent Cl-HCO3 exchanger and that this transporter may be as important as the Na-H exchanger in determining pHi.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1985

Intracellular calibration of a pH-sensitive dye in isolated, perfused salamander proximal tubules.

We evaluated the dye 4',5'-dimethyl-5-(and -6-) carboxyfluorescein (Me2CF) for determining the intracellular pH(pHi) of isolated, perfused proximal tubules of the salamander. The intracellular absorbance spectrum, corrected for the intrinsic absorbance of the tubule, was obtained once per second. The dye was incorporated into tubule cells by exposing them to the membrane-permeable precursor 4',5'-dimethyl-5- (and -6-) carboxyfluorescein diacetate. The introduction of the dye had no significant effect on either pHi or cell voltage transients. Compared with dye contained in a cuvette, intracellular dye had a peak absorbance that was red-shifted by approximately 5 nm, and an apparent pK that was increased by approximately 0.3. These differences precluded an accurate calculation of pHi by the comparison of intracellular spectra with in vitro calibration spectra. However, when Me2CF was calibrated intracellularly, using the K-H exchanger nigericin to equalize external pH and pHi, the dye-derived, steady state pHi was within approximately 0.1 of the value obtained with pH-sensitive microelectrodes. Furthermore, when pHi was simultaneously measured with dye and microelectrodes during rapid pHi transients, the pHi time courses measured by the two methods were very similar. We conclude that the intracellular absorbance spectrum of Me2CF can be used to measure steady state pHi and rapid pHi transients reliably, provided the dye is calibrated intracellularly.

Ambystoma↗
PubMed1985

Basolateral Na-H exchange in the rabbit cortical collecting tubule.

We used the intracellular absorbance spectrum of the dye 4',5'-dimethyl-5- (and -6-) carboxyfluorescein (Me2CF) to measure intracellular pH (pHi) in the isolated, perfused cortical collecting tubule (CCT) of the rabbit nephron. The incident spot of light was generally 10 micron in diameter, large enough to illuminate from two to six cells. No attempt was made to distinguish principal from intercalated cells. All experiments were carried out in HCO3- -free Ringer to minimize HCO3- transport. When cells were acid-loaded by briefly exposing them to Ringer containing NH+4 and then withdrawing the NH+4, pHi spontaneously recovered from the acid load. The pHi recovery was best fit by the sum of two exponentials. When the acid loading was performed in the absence of Na+, the more rapid of the two phases of pHi recovery was absent. The remaining slow phase never returned pHi to normal and was sometimes absent. Returning Na+ to the lumen had only a slight effect on the pHi recovery. However, when Na+ was returned to the basolateral (i.e., blood-side) solution, pHi recovered rapidly and completely. The apparent Km for basolateral Na+ was 27.3 +/- 4.5 mM. The basolateral Na-dependent pHi recovery was reversibly inhibited by amiloride. We conclude that the mechanism responsible for the rapid phase of pHi recovery is an Na-H exchanger confined primarily, if not exclusively, to the basolateral membrane of the CCT.

Amiloride↗