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At least 19 recordsLinked to original sources
PubMed1990

Bumetanide-induced natriuresis and antinatriuresis in the proximal and distal parts of the human nephron. Investigations in acute and chronic bumetanide treatment.

In the present study we used the Li clearance technique to evaluate the effects of submaximal bumetanide infusion on proximal and distal Na reabsorption in healthy volunteers with and without volume and Na replacement. These effects were studied both in chronic bumetanide-treated and in previous nontreated subjects. Li was given as Li carbonate p.o. Glomerular filtration was evaluated by creatinine clearance. Infusion of bumetanide increased fractional Na excretion and fractional Li excretion in the volume-replaced subject. Without volume-replacement bumetanide infusion increased these excretion rates to a significantly lower level. These results suggest that in humans acute submaximal doses of bumetanide cause inhibition of both proximal and distal tubular reabsorption of Na. Along with diuretic-induced volume contraction the natriuretic response is diminished perhaps due to a secondary increase in fractional Na reabsorption which occurs only in the proximal tubular portions of the nephron. In chronic bumetanide-pretreated subjects, however, the fractional Na and Li excretion increased significantly more than in the previous nontreated subjects. Compared to these ion excretions in diuretic-induced Na and volume-depleted subjects the results suggest that a secondary increase in fractional Na reabsorption is developed rapidly during submaximal bumetanide infusion in chronic bumetanide-treated subjects. In the distal part of the nephron, however, the bumetanide-induced increase in Na excretion is much less in the chronic bumetanide-treated subjects than in previous nontreated. Because of these results it is suggested that simple dose-effect relationship for loop-diuretics will be difficult to describe.

Adult↗
PubMedDate not supplied

Interaction studies with bumetanide and furosemide. Effects of probenecid and of indomethacin on response to bumetanide in man.

Bumetanide was administered intravenously in doses of 0.5 and 1.0 mg to eight normal subjects with and without pretreatment with probenecid or indomethacin. Probenecid did not affect either the cumulative response or the time course of response to bumetanide. This may mean that probenecid and potentially other exogenous or endogenous organic acids do not affect the renal handling of bumetanide in normal man. Indomethacin pretreatment decreased the cumulative 4-hour excretion of sodium caused by 1.0 mg bumetanide from 276 +/- 22.9 to 202 +/- 20.9 mEq (P less than 0.003). Effects on volume and chloride paralleled those of sodium, while potassium excretion was not affected. When the response was analyzed as increment in fractional excretion over basal solute excretion, determined from separate control studies, indomethacin still decreased the response, possibly indicating that endogenous prostaglandins may play a role in determining the overall response to bumetanide.

Adult↗
PubMed1975

The supra-additive natriuretic effect addition of bendroflumethiazide and bumetanide in congestive heart failure. Permutation trial tests in patients in long-term treatment with bumetanide.

The additive natriuretic effect of a single dose of bendroflumethiazide, 5 mg., has been studied in patients with advanced congestive heart failure in long-term treatment with bumetanide, 4 mg., daily. Three permutation trial tests were performed including six patients each. In the first trial, the response to supplementary bendroflumethiazide, 5 mg., was definitely superior to that of additional bumetanide, 4 mg., in terms of renal output of sodium, chloride, potassium, water, and osmolar clearance. In the second trial, a similar pattern was found in patients receiving a combination of bumetanide, 4 mg., and spironolactone, 100 mg., daily. The third trial compared the effects of bendroflumethiazide, 5 mg., plus bumetanide, 4 mg.; of bendroflumethiazide, 5 mg.; and of bumetanide, 4 mg. In terms of natriuresis and chloruresis, the response to the combination of two drugs was significantly larger than the sum of the effects of other treatments. It is concluded that the combined effects of the drugs represent a supra-additive effect addition for sodium and chloride. A tentative explanation of the mechanism of interaction in terms of inhibition of renal tubular supplementary spironolactone, involve a tendency to development of hypokalemia, hypochloremia, and alkalosis, it is recommended that supplementary use of bendroflumethiazide in this setting is combined with the administration of potassium chloride or potassium-saving diuretics.

Adult↗
PubMed1991

Measurement of bumetanide in plasma and urine by high-performance liquid chromatography and application to bumetanide disposition.

A high-performance liquid chromatographic method for the measurement of bumetanide in plasma and urine is described. Following precipitation of proteins with acetonitrile, bumetanide was extracted from plasma or urine on a 1-ml bonded-phase C18 column and eluted with acetonitrile. Piretanide dissolved in methanol was used as the internal standard. A C18 Radial Pak column and fluorescence detection (excitation wavelength 228 nm; emission wavelength 418 nm) were used. The mobile phase consisted of methanol-water-glacial acetic acid (66:34:1, v/v) delivered isocratically at a flow-rate of 1.2 ml/min. The lower limit of detection for this method was 5 ng/ml using 0.2 ml of plasma or urine. Nafcillin, but not other semi-synthetic penicillins, was the only commonly used drug that interfered with this assay. No interference from endogenous compounds was detected. For plasma, the inter-assay coefficients of variation of the method were 7.6 and 4.4% for samples containing 10 and 250 ng/ml bumetanide, respectively. The inter-assay coefficients of variation for urine samples containing 10 and 2000 ng/ml were 8.1 and 5.7%, respectively. The calibration curve was linear over the range 5-2000 ng/ml.

Bumetanide↗
PubMed1996

Pharmacokinetics of bumetanide in critically ill infants.

OBJECTIVE: Define the pharmacokinetics of bumetanide after single intravenous doses in volume-overloaded critically ill infants. METHODS: A prospective, open-label study was carried out in a group of 58 infants aged 0 to 6 months who required diuretic therapy. Each patient received a single dose of intravenous bumetanide. Doses selected in sequential order ranged from 0.005 to 0.10 mg/kg. Hematologic and serum chemistry studies were performed before and at 6 and 24 hours after bumetanide administration. Determinations of urine volume and chemistries were performed before (collected from -2 to -4 hours to time 0) and at 1, 2, 3, 4, 6, and 12 hours after bumetanide dosing. Serum samples collected at time 0 and at 5, 15, 30, 60, 120, 180, 240, 360, and 480 minutes and urine collected at time 0 and at 0 to 1, 1 to 2, 2 to 3, 3 to 4, 4 to 6, and 6 to 12 hours were analyzed for bumetanide concentration. Data were evaluated by standard noncompartmental pharmacokinetic techniques. RESULTS: Peak serum bumetanide concentrations occurred at 5 minutes after bumetanide administration. Area under the curve and peak serum bumetanide concentrations showed linear increases over the twentyfold dose range; whereas beta volume of distribution, volume of distribution at steady state, clearance, renal clearance, half-life, and mean residence time values were independent of dose. Peak urinary excretion rates of bumetanide increased linearly with increasing doses. The mean percent of bumetanide recovered in the urine from 0 to 12 hours was 40% +/- 15% of the administered dose. CONCLUSIONS: Distribution and elimination kinetics of bumetanide were similar in all patients. Elimination kinetics were first order over the dose range of 0.005 to 0.10 mg/kg. Pharmacokinetic parameter estimates (beta volume of distribution, volume of distribution at steady state, clearance, renal clearance, half-life, and mean residence time) were independent of the dose of bumetanide administered. Single doses of bumetanide up to 0.10 mg/kg appear to be well tolerated in acutely ill volume-overloaded infants aged 0 to 6 months.

Area Under Curve↗
PubMed1996

Dose-ranging evaluation of bumetanide pharmacodynamics in critically ill infants.

OBJECTIVES: Determine the diuretic effects of single intravenous doses of bumetanide in volume-overloaded critically ill infants. METHODS: A prospective, open-label study was carried out in 56 infants aged 0 to 6 months who required diuretic therapy. Each patient received a single intravenous dose of bumetanide. Doses selected in sequential order ranged from 0.005 to 0.10 mg/kg. Determinations of urine volume, electrolytes, creatinine levels, and osmolality were performed before (collected from -2 to -4 hours to time 0) and at 1, 2, 3, 4, 6, and 12 hours after bumetanide dosing. Serum samples collected at time 0 and at 5, 15, 30, 60, 120, 180, 240, 360, and 480 minutes and urine aliquots collected at time 0, 0 to 1, 1 to 2, 2 to 3, 3 to 4, 4 to 6, and 6 to 12 hours were analyzed for bumetanide concentration. Individual changes in urine flow rate and electrolyte excretion were plotted against corresponding bumetanide excretion rates, taken as the effective dose of the drug. RESULTS: Peak bumetanide excretion rates increased linearly with increasing doses of drug. Time course patterns for urine flow rate and electrolyte excretion were similar for all dosage groups. Urine flow rate and electrolyte excretion increased linearly up to a bumetanide excretion rate of approximately 7 micrograms/kg/hr and either plateaued (urine flow rate) or declined at a bumetanide excretion rate of > 10 micrograms/kg/hr. Diuretic efficiency of bumetanide was maximal at doses of 0.005 to 0.010 mg/kg but decreased at higher doses. CONCLUSIONS: Maximal diuretic responses occurred at a bumetanide excretion rate of about 7 micrograms/kg/hr, corresponding to doses of 0.035 to 0.040 mg/kg. Higher doses produced a proportionately higher bumetanide excretion rate but no increased diuretic effect. Lower doses of bumetanide had the greatest diuretic efficiency, suggesting that continuous infusion of low doses of bumetanide or intermittent low-dose boluses may produce optimal diuretic responses in critically ill infants.

Bumetanide↗
PubMed1991

Effects of phenobarbital and 3-methylcholanthrene pretreatment on the pharmacokinetics and the pharmacodynamics of bumetanide in rats.

The effects of pretreatment with the enzyme inducers, phenobarbital (PB) and 3-methylcholanthrene (3-MC), on the pharmacokinetic and pharmacodynamic parameters of bumetanide were examined in rats. The nonrenal clearance (19.3 vs 29.6 ml min-1 per kg) of bumetanide increased significantly in PB treated rats. This suggested that the nonrenal metabolism of bumetanide is increased by pretreatment with PB, which was supported by significantly increased amounts of bumetanide glucuronide and desbutyl bumetanide excreted in 8-h urine, and reduced amounts of bumetanide remaining per gram of tissue after 30-min incubation of 100 micrograms of bumetanide with the 9000 xg supernatant fraction of liver, stomach, and kidney tissue homogenates in PB treated rats. The contents of hepatic cytochrome P-450 (1.29 vs 2.15 nmol mg-1 protein) and the weights of liver and stomach increased significantly in PB treated rats, suggesting that the metabolizing enzymes for bumetanide are induced by pretreatment with PB. The 8-h urine output per 100 g body weight was not significantly different by pretreatment with PB although the amounts of bumetanide excreted in 8-h urine increased significantly in PB treated rats. It could be explained by the fact that the dose of bumetanide used results in urinary concentrations at the plateau of the concentration-effect relationship. Therefore, the alteration in the urinary excretion rate of bumetanide by pretreatment with PB would not alter the diuretic effect. In 3-MC treated rats, pharmacokinetic and pharmacodynamic parameters were not significantly different and it suggested that the metabolizing enzymes for bumetanide are not induced by pretreatment with 3-MC although the contents of hepatic cytochrome P-450 and the weights of liver and stomach increased significantly by pretreatment with 3-MC.

Animals↗
PubMed1996

Analysis of the variability in the pharmacokinetics and pharmacodynamics of bumetanide in critically ill infants.

OBJECTIVES: Account for the interindividual variability in the pharmacokinetics and pharmacodynamics of bumetanide after intravenous administration of single doses to critically ill infants. METHODS: This prospective open-label study was carried out in the pediatric intensive care unit of a university-based children's hospital. Fifty-three volume-overloaded critically ill infants (age range, 4 days to 6 months) were divided into two groups: those with heart disease (31 infants) and those with lung disease (22 infants). Each patient received a single intravenous bolus dose of bumetanide. Doses, selected in sequential order, ranged from 0.005 to 0.100 mg/kg. Age was used as a continuous variable to determine its effects on the variability in the pharmacokinetics and pharmacodynamics of bumetanide. Hierarchical multiple regression analyses were used to assess the effects of age, disease, and other drugs on the variability in the effects of bumetanide. RESULTS: Total clearance, renal clearance, and nonrenal clearance of bumetanide all increased with age (p < 0.05), but the ratio of renal clearance to total clearance remained constant at about 0.4. Half-life and mean residence time decreased markedly in the first month of life (p < 0.05). Bumetanide excretion rate normalized for dose also increased with increasing age. Patients with lung disease exhibited a significantly greater clearance and shorter half-life (p < 0.05) than those with heart disease, whereas volume of distribution was similar in both groups. The primary determinant of bumetanide excretion rate was the administered dose (73%). Dose-response curves for urine flow rate and electrolyte excretion were similar between disease groups. The time course of the effect of bumetanide excretion rate on pharmacodynamics responses was similar between disease groups, as was the duration of the diuretic effect. CONCLUSIONS: The pharmacokinetics of bumetanide were influenced significantly by age and disease. Differences in pharmacokinetics between patients with lung and heart disease were primarily due to differences in total clearance. The administered dose of bumetanide and age were positive determinants of bumetanide excretion rate and pharmacodynamic responses. Pharmacodynamic responses as a function of bumetanide excretion rate were not significantly different between disease groups.

Aging↗
PubMed1989

Uptake of bumetanide into isolated rat hepatocytes and primary liver cell cultures.

Uptake of bumetanide into rat liver cells was investigated using isolated hepatocytes and primary cell cultures. The kinetics of [3H]-bumetanide uptake revealed two saturable components in addition to an unsaturable component. Saturable bumetanide uptake consists of a high-affinity, sodium-dependent uptake and a low-affinity transport system. Bumetanide uptake into isolated rat hepatocytes is energy dependent and temperature sensitive. At low temperatures, bumetanide uptake is due to diffusion with a permeability coefficient of 1.16 x 10(-6) cm/s. In primary liver cell cultures, uptake of bumetanide decreases rapidly over 3 days. AS-30D ascites hepatoma cells do not take up bumetanide but bind small amounts of the loop diuretic. Hepatocytes metabolized bumetanide extensively. The metabolites were secreted into the surrounding incubation buffer. Two hydroxylated and at least one conjugated biotransformation product could be separated by thin-layer chromatography. Isolated rat hepatocytes possess carrier proteins for uptake of bumetanide and very likely also for uptake of other loop diuretics like furosemide, piretanide, and torasemide. Several inhibitors of multispecific transport systems in the kidney and liver were tested as potential inhibitors of hepatocellular bumetanide or furosemide uptake. Probenecid, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, iodipamide, digitoxin, bile acids, and bromosulfophthalein inhibited uptake of loop diuretics. Inhibition by taurocholic acid was competitive with a Ki of 24 microM. Taurocholic acid inhibited [3H]bumetanide uptake in the presence but not in the absence of Na+. Deoxycholic acid and bromosulfophthalein were noncompetitive inhibitors of hepatocellular bumetanide uptake.(ABSTRACT TRUNCATED AT 250 WORDS)

Affinity Labels↗
PubMed1993

Characterization of bumetanide transport in isolated skate hepatocytes.

The uptake of [3H]bumetanide was studied in isolated skate hepatocytes in an albumin-free elasmobranch Ringer solution and compared with the uptake of bile acids in the presence of other cholephilic organic anions. [3H]bumetanide uptake was energy dependent, temperature sensitive, and exhibited saturation kinetics. In contrast to taurocholate and cholate, which are transported only by Na(+)-independent mechanisms, removal of Na+ reduced the maximal uptake rate (Vmax) for bumetanide from 404 +/- 80 to 230 +/- 47 pmol.mg-1 x min-1 without a change in the apparent Michaelis constant (Km). The apparent Km for the Na(+)-dependent portion of bumetanide uptake was 58 +/- 24 microM, and Vmax was 151 +/- 38 pmol.min-1 x mg-1. Taurocholate (100 and 200 microM) inhibited Na(+)-independent bumetanide transport competitively but was a noncompetitive inhibitor for Na(+)-dependent bumetanide uptake. Furosemide (100 microM) and two bumetanide analogues, PF-3034 (500 microM) and PF-2203 (500 microM), preferentially inhibited the Na(+)-dependent bumetanide uptake system, whereas cholate (100 microM) and probenecid (100 microM) preferentially inhibited Na(+)-independent bumetanide transport. The sulfhydryl (SH) reagents N-ethylmaleimide, 2,2'-dithio-bis(5-nitropyridine), and p-chloromercuribenzenesulfonic acid (PCMBS) inhibited both bile acid and bumetanide uptake. Dithiothreitol (500 microM) completely reversed the PCMBS-induced inhibition of bumetanide uptake. These results indicate that bumetanide is transported into hepatocytes of the small skate, Raja erinacea, by both Na(+)-dependent and Na(+)-independent mechanisms; the latter is shared by bile acids and probably sulfobromophthalein and other organic anions. Their uptake requires free SH groups.

Animals↗
PubMed1984

Bumetanide. A review of its pharmacodynamic and pharmacokinetic properties and therapeutic use.

Bumetanide is a potent 'loop' diuretic for the treatment of oedema associated with congestive heart failure, hepatic and renal diseases, acute pulmonary congestion and premenstrual syndrome and in forced diuresis during and after surgery. Bumetanide may be given orally, intravenously or intramuscularly and produces a rapid and marked diuresis, and increased urinary excretion of sodium, chloride and other electrolytes (within 30 minutes) which persists for 3 to 6 hours. Its principal site of action is on the ascending limb of the loop of Henle, with a secondary action on the proximal tubule. Pharmacologically, bumetanide is about 40-fold more potent than frusemide (furosemide), with the exception of its effects on urinary potassium excretion where its potency is lower. Studies in patients with oedema due to congestive heart failure, pulmonary oedema or hepatic disease show that oral or intravenous bumetanide 0.5 to 2 mg/day produces results comparable to those with frusemide 20 to 80 mg/day. In acute pulmonary oedema, intravenous bumetanide produces a very rapid diuresis. Higher doses of bumetanide may be required (up to 15 mg/day) in patients with chronic renal failure or nephrotic syndrome. In these patients muscle cramps are not uncommon with bumetanide, but glomerular filtration rates are unaffected. In most studies, diuretic effects were accompanied by decreased bodyweight, abdominal girth and improvements in a variety of haemodynamic parameters. Comparison of bumetanide with frusemide at a dose ratio of 1 : 40 reveals no significant differences in clinical response with the exception of renal disease, where patients with oedema appear to respond better to bumetanide. Combination with thiazide diuretics enhances the clinical response to bumetanide. Potassium supplements and spironolactone may be beneficial additions to bumetanide where patients at risk of hypokalaemia can be identified. Clinically important side effects are infrequent, with audiological impairment occurring to a lesser extent than with frusemide. Bumetanide thus offers an important alternative to frusemide when a 'loop' diuretic is indicated.

Animals↗
PubMedDate not supplied

Metabolism of bumetanide.

The metabolism of bumetanide is reviewed, with emphasis on the relationship between metabolism and diuretic activity. Substantial evidence has been obtained for the thesis that diuretic activity is dependent on the amount of bumetanide which reaches the renal tubule. Therefore, bumetanide is a potent diuretic in those species, e.g., human and dog, in which a substantial fraction of the administered dose is excreted as unchanged drug in the urine. In contrast, relatively weak diuretic activity is seen in the rat, a species which very effectively biotransforms bumetanide to inactive metabolites. The metabolites which have been identified in human and rat urine are presented, and the point is made that in both species metabolism of bumetanide appears to be limited to oxidation of the N-butyl side chain. Different (and unidentified) metabolites are excreted by the dog. A prominent metabolite formed in the dog, however, is the acylglucuronide of bumetanide, which was detected in plasma and bile but was not seen in urine or feces. Tissue distribution of bumetanide in the dog is presented so as to show the ability of the kidney to concentrate bumetanide. In the human, bumetanide disposition is also characterized by 95 per cent plasma protein binding and a plasma half-life of 1 to 2 hours. Attention is given to the possibility that the clinical response to bumetanide can be altered by factors which affect drug oxidation by the mixed-function oxygenase system; e.g., induction of the drug-metabolizing enzymes may lead to increased biotransformation of bumetanide and concomitant decreased diuretic activity.

Animals↗
PubMed1985

Stimulation of bumetanide-sensitive K+ transport in Swiss 3T3 fibroblasts by serum and mitogenic hormones.

Rapidly growing Swiss 3T3 fibroblasts possess a bumetanide-sensitive K+ transport system that is dependent on both Na+ and Cl- ions; a smaller bumetanide-insensitive component of K+ transport is also present. In cells brought to the quiescent state by 8-11 days of incubation without a medium change, the bumetanide-sensitive rate of transport was reduced by 63%; the bumetanide-insensitive rate did not change. Removal of dialyzed fetal calf serum from the uptake medium resulted in a substantial reduction in bumetanide-sensitive uptake in both rapidly growing cells (33% reduction) and quiescent cells (68% reduction) but had no effect on bumetanide-insensitive uptake. Insulin was almost as effective as dialyzed fetal calf serum in stimulating bumetanide-sensitive uptake; insulin was maximally stimulatory at 2.5 micrograms/ml. The combination of insulin, epidermal growth factor, and arginine-vasopressin was maximally effective in stimulating both bumetanide-sensitive K+ uptake and 3H-thymidine incorporation in quiescent cells; bumetanide, however, did not interfere with the hormonal stimulation of DNA synthesis. Thus, the bumetanide-sensitive K+ transport system is not necessary for such stimulation to occur. Furthermore, concentrations of hormones which stimulated significant levels of DNA synthesis produced no elevation in the intracellular concentration of K+. We conclude that the bumetanide-sensitive pathway of K+ transport is modulated by serum and by mitogenic hormones, but does not play a role in the stimulation of DNA synthesis by these factors.

Animals↗
PubMed1988

Ionic dependence of bumetanide binding to the rabbit parotid Na/K/Cl cotransporter.

The Na/K/Cl-dependent component of the binding of the loop diuretic bumetanide to basolateral membrane vesicles from the rabbit parotid is studied. A Scatchard analysis indicates that this binding is due to a single high-affinity site with KD = 3.2 +/- 0.3 microM (n = 9) at 100 mM sodium, 100 mM potassium and 5 mM chloride. When KCl-dependent 22Na transport and tracer [3H]-bumetanide binding are monitored simultaneously as a function of (unlabeled) bumetanide concentration it is found that the K0.5 for bumetanide inhibition of both processes are identical indicating that the high-affinity bumetanide binding site studied here is identical with a bumetanide-inhibitory site on the Na/K/Cl cotransport system previously identified in this preparation (R.J. Turner. J.N. George and B.J. Baum, J. Membrane Biol. 94:143-152, 1986). High-affinity bumetanide binding exhibits a hyperbolic dependence on both [Na] and [K] consistent with Na/bumetanide and K/bumetanide binding stoichiometries of 1:1 and K0.5 values of approximately 33 mM for sodium and 23 mM for potassium. In contrast, the dependence on [Cl] is biphasic, with bumetanide binding increasing from 0 to 5 mM chloride and decreasing toward baseline levels thereafter. Scatchard analysis of this latter inhibitory effect of chloride indicates a competitive interaction with bumetanide in agreement with earlier indications that bumetanide inhibits Na/K/Cl cotransport at a chloride site. However, studies of the effects of various anions on bumetanide binding and 22Na transport show a poor correlation between the specificities of these two processes, suggesting that the inhibitory chloride site is not a chloride transport site.

Animals↗
PubMed1981

Potassium chloride cotransport in steady-state ascites tumor cells. Does bumetanide inhibit?

Bumetanide is a potent diuretic drug which has some structural features in common with furosemide. The steady-state exchange of K+ and Cl- was investigated in Ehrlich ascites tumor cells treated with bumetanide. This agent did not alter the cellular content of K+ or Cl- but the self-exchange of both ions was depressed. K+ self-exchange was inhibited by 55% at bumetanide concentrations as low as 10(-6) M. Cl- self-exchange was less sensitive to this drug but at low concentrations (between 10(-6) and 10(-3) M) bumetanide was a more effective inhibitor of Cl- transfer than furosemide. The steady-state K+ flux of cells equilibrated in NO3- media was compared with the K+ flux in cells treated with 10(-4) or 10(-3) M bumetanide; the Cl(-)-sensitive K+ exchange was equivalent to the bumetanide-sensitive K+ exchange. Since the results suggested that a bumetanide-sensitive (Cl-, K+) cotransport could be operative in steady-state cells, the stoichiometry of the bumetanide-sensitive fluxes was determined by measuring Cl- and K+ fluxes simultaneously in the same cell suspension. At 5 . 10(-4) and 10(-3) M bumetanide concentrations, the ratio of these fluxes was 0.98 +/- 0.07 (S.E.) and 1.04 +/- 0.06, respectively, consistent with the postulated cotransport mechanism. At 10(-4) and 10(-5) M, however, the ratio of the bumetanide-sensitive Cl-/K+ flux was significantly less than 1.0. Since the magnitude of the bumetanide-sensitive K+ flux at 10(-4) M was close to that of the Cl(-)-sensitive flux, a ratio of less than 1.0 at this drug level indicates that Cl-sensitivity and drug sensitivity may not reflect inhibition of the same process under all circumstances.

Animals↗