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PubMed1982

Granule fusion and fission (discharge) are biochemically dissociable events of exocytotic hormone release.

Granule fusion and the subsequent fission leading to hormone discharge are distinct and separable events in exocytosis. As an index of fusion, we followed the recruitment of granule-bound somatostatin receptors to the islet surface, an event which accompanies secretion vesicle migration and insulin secretion. Granule fission was monitored by measuring insulin release. Substitution of the impermeant salt sodium isethionate for NaCl led to a 90% decrease in glucose-stimulated insulin release with no inhibition of somatostatin receptor recruitment. The phenothiazine drugs, trifluoperazine and promethazine, believed to inhibit calcium-sensitive proteins involved with stimulus-secretion coupling blocked insulin release and somatostatin receptor recruitment in parallel. This suggests that these agents suppress intracellular events promoting fusion of the secretion granule with the plasma membrane. IBMX appears to stimulate specifically granule fission since IBMX-induced insulin release occurs acutely without an increase in somatostatin receptor recruitment. Sodium isethionate, which inhibits granule lysis, blocked IBMX-stimulated insulin release.

1-Methyl-3-isobutylxanthine↗
PubMed1981

[Tonic mechanisms of efferent inhibition in the frog labyrinth].

Activation of the efferent system of the isolated group labyrinth inhibits the afferent EPSP and spike discharge by releasing ACh, which opens the Cl- channel of the hair cells membrane. Experiments in which increasing amounts of Cl- in the bath are replaced by equivalent amounts of Br-, NO2-, NO3-, CH3 CO2-, SO4(2-), CH3CH2CO2-, CH3(CH2)2CO2-, CH3(CH2)3CO2- benzoate, indicate that all these anions are able to penetrate the postsynaptic membrane, since full inhibition was invariably elicited. On the other hand, when citrate or isethionate are substituted for Cl- inhibition disappeared. In the presence of anions which are known to chelate calcium, its bath concentration was adequately increased. The presence of inhibition of Ringer-benzoate (benzoate ion size 6.5 A) and its disappearance in Ringer-citrate (8 A) or in Ringer-isethionate (greater than 10 A), suggests that the Cl- channel is at least 7 A in diameter, a size significantly larger than at other inhibitory synapses. Since metabolic inhibitors (DNP 0.1 mM and NaN3 1 mM) or acetazolamide (5 mM) and ammonium acetate (10 mM), which are known to block active Cl- pumping in other systems, do not affect the efferent synapse it appears difficult to interfere with the mechanisms which maintain the Cl- concentration gradient across the hair cell membrane.

Animals↗
PubMed1993

Sulfonate-sulfur assimilation by yeasts resembles that of bacteria.

Three sulfonates were tested for their ability to serve as nutrients for Hansenula wingei, Rhodotorula glutinis, Trigonopsis variabilis and Saccharomyces cerevisiae. Cysteate, taurine and isethionate, under aerobic conditions, could be utilized as sources of sulfur, although in some instances final cell yields were less than those obtained with an equimolar amount of sulfate-sulfur. Sulfonate assimilation by S. cerevisiae resembled that of bacteria (reported earlier by us) in several aspects: first, sulfate-S was used in preference to that of sulfonate, when both were present; second, mutants unable to use sulfate as a source of sulfur because of deficiencies in ATP sulfurylase, adenylylsulfate kinase (APS kinase) or PAPS reductase were able to utilize sulfonates; and third, mutants deficient in sulfite reductase were unable to utilize sulfonates.

Aerobiosis↗
PubMed1976

Action of amino acids and convulsants on cerebellar spontaneous action potentials in vitro: effects of deprivation of C1-, K+ of Na+.

(1) The inhibition of spontaneous action potentials in guinea pig cerebellar cortex slices by GABA, glycine, taurine and beta-alanine is maintained when C1- in the superfusion medium is almost completely replaced by NO3- or I-('permeant' anion), but the inhibition decreases in magnitude with repeated application of the amino acid. Replacement of C1- by sulfate or isethionate ('impermeant' anion) causes a conversion of inhibition by these amino acids to excitation. The initial excitation which is sometimes seen with these inhibitory amino acids in high C1- media is abolished when C1- is replaced by either permeant or impermeant anions. (2) Reduction of K+ in the medium causes an increase of inhibition by the inhibitory amino acids in the presence of high C1- and reduction of excitation when C1- is replaced by impermeant anion. (3) Excitation by GABA in impermeant anion (low C1-) media is unaffected by reduction of Na+ in the media by 50% but excitations by glycine, taurine, beta-alanine and L-glutamate are greatly reduced. (4). Excitation by GABA in impermeant anion (low C1-) media is abolished by picrotoxin and bicuculline which both suppress inhibition by GABA in a high C1- medium. Strychnine suppresses the effects of glycine, taurine and beta-alanine in either a low or high C1- medium. Bicuculline blocks the inhibitory effect of these three amino acids in a high C1- medium but does not affect their excitatory effects in a low C1- medium. (5) These results are consistent with the hypothesis that the inhibitory amino acids, GABA, glycine, taurine and beta-alanine, cause inhibition via increase of C1- (and perhaps K+) permeability and that glycine, taurine and beta-alanine also interact with strychnine-sensitive receptors mediating (perhaps indirectly) increased permeability to Na+ and, therefore, excitation in low C1- media.

Action Potentials↗
PubMed1993

Cl- replacement alters the ventilatory response to central chemoreceptor stimulation.

To determine whether cerebrospinal fluid (CSF) Cl- has a role in determining the stimulus to the central respiratory chemoreceptors under conditions of constant CSF pH, CO2, and HCO3- concentrations, the ventral medullary surface of the anesthetized rat was perfused with mock CSF of various ion composition and pH. Four mock CSF perfusates were used: two normal pH control perfusions and two acidic solutions. One acidic perfusate was formulated in the traditional manner by substituting Cl- for HCO3-. The second acidic perfusate, and one of the normal pH control perfusates, had approximately 15% of the Cl- replaced with isethionate, an impermeant strong anion. When the two acidic solutions were perfused over the ventral medulla, consistently larger increases in both tidal volume and minute ventilation were observed with the isethionate-containing acidic solution, despite conditions of identical pH and PCO2. The unequal ventilatory effects of the two acidic perfusions suggest that Cl- transport may be a factor determining the stimulus to the central respiratory chemoreceptors.

Animals↗
PubMed1994

Anti-tumor necrosis factor properties of non-peptide drugs in acute-phase responses.

Dexamethasone (sodium phosphate), pentoxifylline, fusidic acid (sodium salt), pentamidine (isethionate) and R-phenylisopropyladenosine (R-PIA) were tested for their anti-tumor necrosis factor (TNF) activities in an endotoxin-induced shock rat model. All the drugs reduced serum TNF concentrations in a dose-dependent manner, whereas their effects on serum interleukin-6 levels differed. Doses that reduced TNF levels by 50% were 0.012 mg/kg for dexamethasone, 0.06 mg/kg for R-PIA, 0.24 mg/kg for pentamidine, 6.5 mg/kg for fusidic acid and 15 mg/kg for pentoxifylline. Administration of the drugs to rats before intraplantar injection of carrageenan reduced paw edema by 50-70%. Injection of a monoclonal anti-TNF antibody reproduced the inhibitory effect. Moreover, the time course of tissue-associated TNF following carrageenan injection was compatible with mediation of edema by TNF. Results obtained for this acute, non-immunological inflammatory reaction strongly suggest that the model is TNF-dependent. Our results reinforce the idea that TNF is a crucial target in the therapeutics of inflammatory reactions. These drugs, which are able to cross cell barriers, might have clinical applications in localized and/or chronic diseases in which TNF is involved.

Acute-Phase Reaction↗
PubMed1985

Influence of phosphate, sulfonic, and sulfamic acids on sulfoconjugate release in the vascularly perfused mouse small intestine.

An in vitro vascularly and luminally perfused preparation of the murine small intestine was used to investigate the interference of isethionate, cyclamate and HEPES (N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid) with the luminal transport of the isoprenaline-sulfoconjugate as well as with the basolateral transport of naphthol-sulfoconjugate. The sulfonates and sulfamates when administered from the luminal as well as from the contraluminal side of the epithelium inhibited the transport of isoprenaline-sulfoconjugate. Inhibition of the naphthol-sulfoconjugate transport across the contraluminal epithelial membrane was less pronounced, but a countertransport phenomenon could be induced with cyclamate in the vascular medium. The presence of phosphate at the luminal side is essential for the transport of the isoprenaline-sulfoconjugate across the luminal membrane. This is not the case for bicarbonate. The conclusion is drawn that different transport systems for sulfoconjugates exist in the luminal and in the contraluminal membranes of the intestinal mucosa, which can be inhibited by structurally related compounds. The luminal transport system can be activated from the luminal side by phosphate.

Animals↗
PubMed1991

Genetic characterisation of resistance to metal ions in methicillin-resistant Staphylococcus aureus: elimination of resistance to cadmium, mercury and tetracycline with loss of methicillin resistance.

Susceptibility to six metal ions--cadmium (Cd), mercury (Hg), arsenate (Asa), arsenite (Asi), antimony (Sb) and zinc (Zn)--was tested in 23 independent isolates of methicillin-resistant Staphylococcus aureus (MRSA) obtained from Guy's Hospital (GH) during 1984-1986, which included 10 isolates of the UK epidemic EMRSA-1 strain. Strains were also tested for resistance to antibiotics and the nucleic-acid-binding compounds propamidine isethionate and ethidium bromide. A further 19 methicillin-resistant isolates, including 10 EMRSA-1 were obtained from other sources. Ten methicillin-sensitive, antibiotic sensitive isolates were from Guy's Hospital. Resistance to Hg was associated with methicillin resistance in 19 of the 20 EMRSA-1 isolates, all of which were resistant to Cd. Resistance to Cd and Hg was found in 13 out of 22 other MRSA isolates. Hg resistance was not present in the methicillin-sensitive isolates which were often (13 out of 19) moderately resistant to Cd. Multiple resistance to metal ions, including resistance to Hg, Asa, Asi and Sb, was uncommon. Resistance to Cd (MIC greater than 32 mg/L or 8-16 mg/L) was associated with increased resistance to Zn. In 11 of the consecutive MRSA isolates from Guy's Hospital seven distinct strains were recognised by phage type. Methicillin resistance in these strains varied from 16 to 1024 mg/L at 30 degrees C with a 2-8-fold lower minimum inhibitory concentration at 37 degrees C indicating some degree of heterogeneity. Representatives of the EMRSA-1 strain had the higher levels of resistance. Loss of methicillin resistance occurred in 0.2-5.0% of colonies tested after storage at room temperature in 10 of these isolates.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacteriophages↗
PubMed1997

Role of anions in the regulation of cell volume and intracellular pH in perfused rat mandibular salivary gland.

To investigate the role of Cl- in the regulation of the basolateral transporters of salivary acinar cells, we have measured cell volume and intracellular pH (pHi) in perfused rat mandibular glands using proton NMR spectroscopy and BCECF fluorometry respectively. When perfusate Cl- was replaced by glucuronate, isethionate, methylsulphate, nitrate or thiocyanate, cell volume decreased slowly by about 15% over a 10-min period. Replacement with bromide, which substitutes for Cl- on the Na+-K+-2Cl- cotransporter, caused only a small (4%) reduction in cell volume. Replacement of Cl- by glucuronate, isethionate or methylsulphate evoked a biphasic increase in pHi consisting of a rapid initial increase followed by a slower secondary rise whose time course was similar to that of cell shrinkage. As judged by the effects of HCO3- omission, 100 microM 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) and 1 mM amiloride, the initial rise in pHi was due to Cl-/HCO3- exchange while the secondary rise resulted from activation of Na+/H+ exchange. Although replacement of Cl- by nitrate or thiocyanate also caused cell shrinkage, these substituting anions were less effective in activating the exchanger. Therefore, while the upregulation of the exchanger following Cl- replacement may be due in part to cell shrinkage, there is also evidence for the involvement of an anion-sensitive regulatory mechanism. This would be consistent with the hypothesis that both changes in cell volume and in intracellular Cl- concentration contribute to the up-regulation of the exchanger following muscarinic stimulation.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1999

Chloride channel blockers attenuate the inhibition of renin secretion by angiotensin II.

The aim of this study was to assess the relevance of chloride channels to the inhibitory effect of angiotensin II (ANGII) on renin secretion. We thus examined the effects of the chloride channels blockers IAA-94 and niflumic acid, the Na-K-Cl cotransport blocker bumetanide and substitution of isethionate for extracellular chloride on the action of ANGII on renin secretion from isolated perfused rat kidneys. Renin secretion prestimulated by isoproterenol (10 nmol/l) was almost completely blocked by ANGII with a concentration yielding a half-maximal response (EC50) of around 150 nmol/l. In the presence of IAA-94 and niflumic acid the EC50 for ANGII was shifted to about 400 nmol/l. In the presence of bumetanide and isethionate renin secretion responded more sensitively to ANGII and the EC50 for ANGII was below 100 nmol/l. On the assumption that the chloride equilibrium potential in renin-secreting cells is more positive than the membrane potential, our findings would suggest that the inhibitory effect of ANGII is enhanced when chloride entry is blocked and attenuated when chloride efflux is impaired. Activation of chloride channels therefore probably contributes to the inhibitory action of ANGII on renin secretion.

Angiotensin II↗
PubMed2004

Enzymes and genes of taurine and isethionate dissimilation in Paracoccus denitrificans.

Growth of the alpha-proteobacterium Paracoccus denitrificans NKNIS with taurine or isethionate as sole source of carbon involves sulfoacetaldehyde acetyltransferase (Xsc), which is presumably encoded by an xsc gene in subgroup 3, none of whose gene products has been characterized. The genome of the alpha-proteobacterium Rhodobacter sphaeroides 2.4.1 was interpreted to contain a nine-gene cluster encoding the inducible dissimilation of taurine, and this deduced pathway included a regulator, a tripartite ATP-independent transporter, taurine dehydrogenase (TDH; presumably TauXY) as well as Xsc (subgroup 3), a hypothetical protein and phosphate acetyltransferase (Pta). A similar cluster was found in P. denitrificans NKNIS, in contrast to an analogous cluster encoding an ATP-binding cassette transporter in Paracoccus pantotrophus. Inducible TDH, Xsc and Pta were found in extracts of taurine-grown cells of strain NKNIS. TDH oxidized taurine to sulfoacetaldehyde and ammonium ion with cytochrome c as electron acceptor. Whereas Xsc and Pta were soluble enzymes, TDH was located in the particulate fraction, where inducible proteins with the expected masses of TauXY (14 and 50 kDa, respectively) were detected by SDS-PAGE. Xsc and Pta were separated by anion-exchange chromatography. Xsc was effectively pure; the molecular mass of the subunit (64 kDa) and the N-terminal amino acid sequence confirmed the identification of the xsc gene. Inducible isethionate dehydrogenase (IDH), Xsc and Pta were assayed in extracts of isethionate-grown cells of strain NKNIS. IDH was located in the particulate fraction, oxidized isethionate to sulfoacetaldehyde with cytochrome c as electron acceptor and correlated with the expression of a 62 kDa protein. Strain NKNIS excreted sulfite and sulfate during growth with a sulfonate and no sulfite dehydrogenase was detected. There is considerable biochemical, genetic and regulatory complexity in the degradation of these simple molecules.

Acetaldehyde↗
PubMed1993

Sulphonate utilization by enteric bacteria.

A variety of sulphonates were tested for their ability to serve as nutrients for Escherichia coli, Enterobacter aerogenes and Serratia marcescens. Cysteate, taurine and isethionate could not serve as sole sources of carbon and energy but, under aerobic conditions, could be utilized as sources of sulphur. Both sulphate and sulphonate supported equivalent cell yields, but the generation times varied with the sulphonate being metabolized. The sulphonate-S of HEPES buffer, dodecane sulphonate and methane sulphonate was also utilized by some strains, whereas the sulphonate-S of taurocholate was not. None of the sulphonates tested served as a sulphur source for growth under anaerobic conditions. Sulphonate utilization appears to be a constitutive trait; surprisingly, however, cells of E. coli and Ent. aerogenes utilized sulphate-S in preference to that of sulphonate, when both were present. E. coli mutants unable to use sulphate as a source of sulphur because of deficiencies in sulphate permease, ATP sulphurylase, adenylylsulphate kinase (APS kinase) or glutaredoxin and thioredoxin were able to utilize sulphonates; hence sulphate is not an obligatory intermediate in sulphonate utilization. However, mutants deficient in sulphite reductase were unable to utilize sulphonates; therefore, this enzyme must be involved in sulphonate utilization, though it is not yet known whether it acts upon the sulphonates themselves or upon the inorganic sulphite derived from them.

Anaerobiosis↗
PubMed1981

Effects of chloride substitutes on PAH transport by isolated perfused renal tubules.

Effects of substituting isethionate, methyl sulfate, or thiocyanate for chloride on p-aminohippurate (PAH) transport by isolated perfused snake (Thamnophis spp.) distal-proximal renal tubules were studied. In the perfusate, isethionate or methyl sulfate substitution irreversibly depressed net PAH secretion and the apparent PAH permeability of the luminal membrane by about 60-80%, whereas thiocyanate substitution had no effect. In the bathing medium, isethionate substitution reversibly stimulated net PAH secretion by about 35% without changing the apparent permeability of the peritubular membrane to PAH (Pp); thiocyanate substitution reversibly inhibited net PAH secretion by about 45% without affecting Pp; and methyl sulfate substitution had no effect. With simultaneous substitutions in perfusate and bath, isethionate depressed net PAH secretion irreversibly, whereas thiocyanate had no effect. Effects on PAH transport were not simply the result of changes in transepithelial potential or of the changes in net transepithelial fluid movement. These data strengthen the concept that net PAH secretion involves different mediated steps at the peritubular and luminal membranes. Since these tubules are highly permeable to thiocyanate and poorly permeable to isethionate and methyl sulfate, the data suggest that the mediated step from cells to lumen does not require chloride in the lumen but does require a highly permeant anion.

Aminohippuric Acids↗
PubMed1997

Taurine reduction in anaerobic respiration of Bilophila wadsworthia RZATAU.

Organosulfonates are important natural and man-made compounds, but until recently (T. J. Lie, T. Pitta, E. R. Leadbetter, W. Godchaux III, and J. R. Leadbetter. Arch. Microbiol. 166:204-210, 1996), they were not believed to be dissimilated under anoxic conditions. We also chose to test whether alkane- and arenesulfonates could serve as electron sinks in respiratory metabolism. We generated 60 anoxic enrichment cultures in mineral salts medium which included several potential electron donors and a single organic sulfonate as an electron sink, and we used material from anaerobic digestors in communal sewage works as inocula. None of the four aromatic sulfonates, the three unsubstituted alkanesulfonates, or the N-sulfonate tested gave positive enrichment cultures requiring both the electron donor and electron sink for growth. Nine cultures utilizing the natural products taurine, cysteate, or isethionate were considered positive for growth, and all formed sulfide. Two clearly different pure cultures were examined. Putative Desulfovibrio sp. strain RZACYSA, with lactate as the electron donor, utilized sulfate, aminomethanesulfonate, taurine, isethionate, and cysteate, converting the latter to ammonia, acetate, and sulfide. Strain RZATAU was identified by 16S rDNA analysis as Bilophila wadsworthia. In the presence of, e.g., formate as the electron donor, it utilized, e.g., cysteate and isethionate and converted taurine quantitatively to cell material and products identified as ammonia, acetate, and sulfide. Sulfite and thiosulfate, but not sulfate, were utilized as electron sinks, as was nitrate, when lactate was provided as the electron donor and carbon source. A growth requirement for 1,4-naphthoquinone indicates a menaquinone electron carrier, and the presence of cytochrome c supports the presence of an electron transport chain. Pyruvate-dependent disappearance of taurine from cell extracts, as well as formation of alanine and release of ammonia and acetate, was detected. We suspected that sulfite is an intermediate, and we detected desulfoviridin (sulfite reductase). We thus believe that sulfonate reduction is one aspect of a respiratory system transferring electrons from, e.g., formate to sulfite reductase via an electron transport system which presumably generates a proton gradient across the cell membrane.

Acetates↗
PubMed1995

Role of membrane-permeable ions in renin secretion by renal juxtaglomerular cells.

In this study we examine the role of membrane-permeable ions in renin secretion from renal juxtaglomerular (JG) cells. To this end, extracellular Cl- (100 mmol/l) in the culture medium of isolated mouse renal JG cells was replaced by the permeable anion NO3- or by the membrane-impermeable anion isethionate. Alternatively, extracellular Na+ (100 mmol/l) was substituted by the membrane-impermeable cation choline. The effects of these ion substitutions on basal and stimulated renin secretion were then examined. Renin secretion was stimulated by the adenylate cyclase activator forskolin (10 microM), the NO donor sodium nitroprusside (SNP, 100 microM), the calmodulin antagonist calmidazolium (10 microM), by lowering extracellular Ca2+ concentration ([Ca2+]e) with ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) (2 mM), and by increasing [Ca2+]e from the normal value of 0.5 to 3 mM. Substitution of extracellular Cl- by isethionate, but not by NO3-, inhibited basal renin release over 20 h of incubation. NO3- also did not change renin secretion stimulated by forskolin, SNP, calmidazolium, EGTA, or by increased [Ca2+]e. Isethionate, on the other hand, markedly attenuated the effects of EGTA and of increased [Ca2+]e, but not the stimulatory effect of forskolin, calmidazolium, or SNP. Substitution of Na+ by choline also attenuated basal renin secretion and renin secretion stimulated by lowering or raising [Ca2+]e. These findings suggest that, with respect to the dependency on permeable ions, at least two different pathways of regulated renin secretion from JG cells exist: a cation- and anion-dependent Ca(2+)-related pathway and a less ion-sensitive pathway for renin secretion activated by adenosine 3',5'-cyclic monophosphate and NO.

Animals↗
PubMed1980

Osmotic lysis of bovine chromaffin granules in isotonic solutions of salts of weak organic acids. Release of catecholamines, ATP, dopamine beta-hydroxylase, and enkephalin-like material.

Chromaffin granules in isotonic solutions of K+ CH3COO- (acetate), K+ CH3CHOHCOO- (lactate), and K+2-OOCCH2CH2COO- (succinate) are stable at pH 7 but release 40 to 80% of their soluble contents of catecholamines, ATP, and dopamine beta-hydroxylase when the medium pH is less than 6. Enkephalin-like material which has recently been shown to co-sediment with chromaffin granules in sucrose density gradients is also released at low pH. The release of ATP and enkephalin-like material is proportional to the release of catecholamine. The release of soluble constituents of chromaffin granules is inhibited by increasing the osmolality of the solution with sucrose. Granules in isotonic solutions of salts of strong acids such as K+CH3SO4- (methylsulfate), K+ CH2OHCH2SO3- (isethionate), and K2SO4 are stable between pH7.0 and 5.4. The granules behave as predicted for organelles with an acid interior and the data provide further evidence that the intragranular pH is acidic. In addition, the results strongly suggest that enkephalin-like material is stored together with catecholamine and ATP in an acid compartment.

Acetates↗
PubMed1988

Prolactin synthesis in cultured pituitary cells is chloride-dependent.

Release of prolactin from both normal pituitary cells and rat pituitary tumor (GH) cells is an osmotic process that is dependent upon chloride. The long term growth rate of GH-cells in medium in which chloride was exchanged with isethionate was completely normal, but, by 48 h, isethionate substitution resulted in a 70% decrease in the concentration of internal and secreted prolactin. Isethionate caused a much smaller reduction in growth hormone production (less than 20%). These results suggest that exchange of chloride with isethionate is inhibiting the synthesis of prolactin. Reduction of intracellular levels of prolactin in cells grown in isethionate-containing medium was evident by 30 h, and the level of prolactin was reduced 92% at 96 h. This reduction in the internal concentrations of prolactin was reversed when the cells were returned to normal medium containing chloride with a t1/2 of 48 h. Addition of epidermal growth factor and the calcium channel agonist BAY K 8644 to cells in medium containing chloride increased internal prolactin by 400%, and isethionate exchange reduced the response by 85%. To confirm that isethionate exchange was inhibiting the synthesis of prolactin, mRNA concentrations for prolactin and actin were determined. Both basal and hormone-stimulated levels of prolactin mRNA were reduced 70 to 90% by isethionate exchange, while actin mRNA levels did not change. To determine whether the effect of isethionate was at the level of gene transcription, GH-cells were transfected with a prolactin-chloramphenicol acetyltransferase fusion gene and chloramphenicol acetyltransferase expression was assessed using cells in chloride and isethionate-containing media. Both basal and hormone-stimulated synthesis of chloramphenicol acetyltransferase driven by the prolactin promoter was inhibited by isethionate exchange. These studies demonstrate that exchange of medium chloride with isethionate inhibits the synthesis of prolactin at the level of transcription.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗