Membrane water and solute permeability determined quantitatively by self-quenching of an entrapped fluorophore

Quantitative determination of rapid water and solute transport and solute reflection coefficients by light-scattering methods is complicated by dependence of vesicle or cell light scattering on nonvolume factors including solution refractive index, cell motion, and membrane aggregation. To overcome these difficulties, a fluorescence technique has been developed to measure accurately (1) osmotic water permeability (Pf), (2) solute permeability (Ps), and (3) solute reflection coefficient (sigma). The time course of vesicle volume is determined by the self-quenching of entrapped fluorescein sulfonate (FS), the best of a series of dyes screened for self-quenching, brightness, and vesicle loading/trapping. To validate the method, rabbit renal brush border vesicles (BBV) were loaded with 1-10 mM FS for 12 h at 4 degrees C and washed to remove extravesicular FS. FS leakage occurred over greater than 6 h at 4 degrees C and greater than 30 min at 23 degrees C. FS fluorescence vs vesicle volume was calibrated from the time course of fluorescence decrease (excitation 470 nm, emission greater than 515 nm) in response to a series of inward osmotic gradients in a stopped-flow apparatus. At 23 degrees C Pf was 0.005 +/- 0.001 cm/s, independent of osmotic gradient size, and inhibited 67% by 0.5 mM HgCl2. Urea Ps was 2 x 10(-6) cm/s with sigma 0.95-1.00 on the basis of the fluorescence time course analysis and the extravesicular [urea] required to obtain zero initial volume flow (null method) when vesicles were loaded with sucrose.(ABSTRACT TRUNCATED AT 250 WORDS)

Sodium-dependent chloride transport in basolateral membrane vesicles isolated from rabbit proximal tubule

The mechanisms for Cl transport across basolateral membrane vesicles (BLMV) isolated from rabbit renal cortex were examined by using the Cl-sensitive fluorescent indicator 6-methoxy-N-(3-sulfopropyl)quinolinium (SPQ). The transporters studied included Cl/base exchange, Cl/base/Na cotransport, K/Cl cotransport, and Cl conductance. Initial rates of chloride influx (JCl) were determined from the measured time course of SPQ fluorescence in BLMV following inwardly directed gradients of Cl and gradients of other ions and/or pH. For a 50 mM inwardly directed Cl gradient in BLMV which were voltage and pH clamped (7.0) using K/valinomycin and nigericin, JCl was 0.80 +/- 0.14 nmol S-1 (mg of vesicle protein)-1 (mean +/- SD, n = 8 separate preparations). In the absence of Na and CO2/HCO3 in voltage-clamped BLMV, JCl increased 56% +/- 5% in response to a 1.9 pH unit inwardly directed H gradient; the increase was further enhanced by 40% +/- 3% in the presence of CO2/HCO3 and inhibited 30% +/- 8% by 100 microM dihydro-4,4'-diisothiocyanostilbene-2,2'-disulfonic acid. Na gradients did not increase JCl in the absence of CO2/HCO3; however, an outwardly directed Na gradient in the presence of CO2/HCO3 increased JCl by 31% +/- 8% with a Na KD of 7 +/- 2 mM. These results indicate the presence of Cl/OH and Cl/HCO3 exchange, and Cl/HCO3 exchange trans-stimulated by Na. There was no significant effect of K gradients in the presence or absence of valinomycin, suggesting lack of significant K/Cl cotransport and Cl conductance under experimental conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal brush-border chloride transport mechanisms characterized using a fluorescent indicator

Cl transport mechanisms in brush-border membrane vesicles (BBMV) isolated from rabbit renal cortex were characterized using the Cl-sensitive fluorescent indicator 6-methoxy-N-[3-sulfopropyl]quinolinium (SPQ). In control experiments using 36Cl, SPQ did not itself alter rates for Cl transport. Cl fluxes (JCl) in nanomoles per second per milligram vesicle protein in response to gradients of Cl and other ions were calculated from the SPQ fluorescence time course, fluorescence vs. [Cl] calibration, and BBMV glucose space (microliter/mg protein). For a 50 mM inwardly directed Cl gradient in BBMV (voltage and pH clamped) JCl was 0.26 +/- 0.01 nmol.s-1.mg-1 (mean +/- SD, 4 vesicle preparations). JCl was not altered by a 50 mM inwardly directed Na gradient (0.25 +/- 0.01 nmol.s-1.mg-1) but increased to 0.52 +/- 0.04 nmol.s-1.mg-1 when driven by a 1.5 pH unit inwardly directed proton gradient. The pH driven increase in JCl was blocked by H2DIDS (100 microM, JCl = 0.38 +/- 0.02 nmol.s-1.mg-1). In the absence of a gradient, JCl increased by 64 +/- 4% in the presence of 1 mM formate on both sides of the membrane; the increase was blocked by H2DIDS. JCl increased to 0.38 +/- 0.02 nmol.s-1.mg-1 for a 60-mV K valinomycin diffusion potential (internal positive); the increase was inhibited by the Cl channel blocker diphenylamine-2-carboxylate (DPC, 100 microM, JCl = 0.26 +/- 0.03 nmol.s-1.mg-1). Br and I transport was also blocked by DPC.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal basolateral membrane anion transporter characterized by a fluorescent disulfonic stilbene

The fluorescence enhancement of 4,4'-dibenzamido-2,2'-disulfonic stilbene (DBDS) upon binding to membranes was used to examine proximal tubule stilbene binding sites. Equilibrium binding studies of DBDS to renal brush border (BBMV) and basolateral membrane vesicles (BLMV) were performed using a fluorescence enhancement technique developed for red blood cells (A.S. Verkman, J.A. Dix and A.K. Solomon, J. Gen. Physiol. 81:421-449, 1983). In the absence of transportable anions, DBDS bound reversibly to a single class of sites on BLMV isolated from rabbit (Kd = 3.8 microM) and rat (3.2 microM); 100 microM dihydro-4,4'-diisothiocyano-2,2'-disulfonic stilbene (H2DIDS) blocked greater than 95% of binding. H2DIDS inhibitable DBDS binding was not detected using rat or rabbit BBMV. In rabbit BLMV, DBDS Kd doubled with 10 mM SO4, 50 mM HCO3 and 100 mM Cl, but was not altered by Na or pH (6-8). In stopped-flow experiments the exponential time constant for DBDS binding slowed with SO4, HCO3 and Cl, but was unaffected by Na. These results are consistent with competitive binding of DBDS and anions at an anion transport site. To relate DBDS binding data to anion transport inhibition we used 35SO4 uptake to characterize several modes of rabbit BLM anion transport: H/SO4 and Na/SO4 cotransport, and Cl/SO4 countertransport. Each transport process was electroneutral and was inhibited by H2DIDS, furosemide, probenecid, chlorothiazide and DBDS. The apparent KI's for DBDS (3-20 microM) were similar to Kd for DBDS binding. These studies define a class of anion transport sites on the proximal tubule basolateral membrane measurable optically by a fluorescent stilbene.

Serologic differences among nondefective reticuloendotheliosis viruses

Antigenic relationships among 26 isolates of reticuloendotheliosis virus (REV) obtained from several avian species were compared by cross neutralization tests with polyclonal chicken sera and by immunofluorescent assays with monoclonal antibodies to REV strain T. The isolates were all strongly related by neutralization assays and thus probably constitute a single serotype. However, 3 antigenic subtypes were suggested by minor but distinct differences in neutralization titers. The validity of these 3 subtype designations was confirmed by differential reactivity of viral isolates to selected monoclonal antibodies. Subtype-associated differences in serum antibody titers were noted following the inoculation of chickens with the REV isolates.

Non-electrolyte transport across renal proximal tubule cell membranes measured by tracer efflux and light scattering

Non-electrolyte transport in brush border membrane vesicles (BBMV), basolateral membrane vesicles (BLMV) and in viable cells isolated from the proximal convoluted tubule (PCT) of the rabbit kidney were measured by rapid filtration and stopped-flow light scattering techniques. Efflux of tracer solute was measured by loading packed vesicles or cells with 14C solute, diluting into nonradioactive buffer and filtering rapidly at varying incubation times. In BBMV at 23 degrees C, [14C-urea] decreased exponentially with time constant 3.2 +/- 0.3 s (S.D., n = 5) corresponding to a permeability coefficient (Purea) of 1.6 X 10(-6) cm/s, assuming a BBMV surface-to-volume ratio of 2 X 10(5) cm-1. Purea decreased to 7 X 10(-7) cm/s in the presence of 20 mM phenylurea. Tracer efflux determinations of BBMV Purea (1.6 X 10(-6) cm/s) and Pglycerol (0.6 X 10(-6) cm/s), and BLMV Purea (1.8 X 10(-6) cm/s) and Pthiourea (2.5 X 10(-6) cm/s) were in excellent agreement with Ps values determined by stopped-flow light scattering, where the time course of vesicle volume (linearly related to scattered light intensity) was measured in response to 100 mM outwardly directed solute gradients. These results establish accurate Ps value in brush border and basolateral membranes and support the application of light scattering to measure Ps in vesicles. In PCT cells however, there were systematic differences in urea and thiourea transport measured by tracer efflux and light scattering, indicating the potential difficulties in applying light scattering to Ps measurements in complex cell systems.

Mechanism of coupling between Cl- and OH- transport in renal brush-border membranes

The coupling mechanism for Cl- and H+/OH- transport in renal brush-border vesicles was examined from intravesicular pH changes following imposed H+ and Cl- gradients. Vesicles were loaded with 6-carboxyfluorescein and exposed to H+ gradients and Cl-, gluconate, or sulfate gradients, each with and without a K+/valinomycin voltage clamp. Parallel experiments were performed with vesicles equilibrated with 10 mM HCO3- or 5 mM formate. Rate of H+/OH- transport was determined from the initial rate of change in 6-carboxyfluorescein fluorescence, vesicle buffer capacity and the relationship between fluorescence and vesicle pH. In contrast to gluconate or sulfate, Cl- caused enhanced H+/OH- transport under all conditions. This difference was eliminated with voltage clamping in the presence of gluconate, SO4(2-), or HCO3-, but not in the presence of formate. These findings were not affected by the method of preparation of the vesicles. Electrically coupled Cl-/OH- transport was not inhibited by 100 microM DIDS (4,4'-diisothiocyanostilbene-2,2'-disulfonate) or 100 microM DBDS (4,4'-dibenzamidostilbene-2,2'-disulfonate). SITS (4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonate) was found to be a protonophore at concentrations greater than 500 microM. As a control for the method, we demonstrated amiloride inhibitable, electroneutral Na+-H+ exchange (H+ flux = 107 +/- 9 nmol/s per mg, 100 mM Na+) and electroneutral, DBDS inhibitable Cl(-)-HCO3- exchange in sealed human red blood cell ghosts. Therefore, electroneutral Cl(-)-OH- or HCO3- exchange does not measurably contribute to Cl- transport in the proximal tubule brush border. Cl(-)-formate exchange with formic acid recycling appears to be the only electroneutral coupling mechanism between Cl- and OH- transport demonstrable in renal brush-border membrane vesicles.

Interaction of O2 diffusion and O2 metabolism in cat urinary bladder tissue

We measured oxygen exchange across the inside surface of excised urinary bladders that were inflated with gas mixtures. By using a range of Po2 differences between the two sides of the tissue and relatively simple mathematical models, we could infer the exchanges across the outside surface and the total O2 economy of the tissue so that we could evaluate the interaction between diffusion and metabolic O2 consumption. The estimate of the Krogh diffusion constant or permeation coefficient with this preparation avoids errors due to O2 consumption and unstirred layers. At 37 degrees C, the value of bladder tissue O2 consumption was 4.4 times 10(-3) min-1 and the value of the Krogh constant for O2 was 2.22 times 10(-5)cm2min-1atm-1.

Krogh constants for diffusion of nitrogen and carbon monoxide in bladder tissue

We have measured diffusion of N2 and CO through the walls of urinary bladders of cats. The excised bladders were inflated with various gas mixtures and suspended in air. Values of the Krogh diffusion constants at 37 degrees C are 1.14 X 10(-5) for N2, and 1.79 X 10(-5) for CO (units are cm2-min-1-atm-1 and standard errors are less than 10% of the values).