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Biomedical subjects

W J Lucas

Publications and source records attributed to W J Lucas.

At least 73 records · Page 4Linked to original sources
PubMed1987

Fluxes of h and k in corn roots : characterization and stoichiometries using ion-selective microelectrodes.

We report here on an experimental system that utilizes ion-selective microelectrodes to measure the electrochemical potential gradients for H(+) and K(+) ions within the unstirred layer near the root surface of both intact 4-day-old corn seedlings and corn root segments. Analysis of the steady state H(+) and K(+) electrochemical potential gradients provided a simultaneous measure of the fluxes crossing a localized region of the root surface. Net K(+) influx values obtained by this method were compared with unidirectional K(+) ((86)Rb(+)) influx kinetic data; at any particular K(+) concentration, similar values were obtained by either technique. The ionspecific microelectrode system was then used to investigate the association between net H(+) efflux and net K(+) influx. Although the computed H(+):K(+) stoichiometry is dependent upon the choice of diffusion coefficients, the values obtained were extremely variable, and net K(+) influx rarely appeared to be charge-balanced by H(+) efflux. In contrast to earlier studies, we found the cortical membrane potential to be highly K(+) sensitive within the micromolar K(+) concentration range. Simultaneous measurements of membrane potential and K(+) influx, as a function of K(+) concentration, revealed similar K(m) values for the depolarization of the potential (K(m) 6-9 micromolar K(+)) and net K(+) influx (K(m) 4-7 micromolar K(+)). These data suggest that K(+) may enter corn roots via a K(+)-H(+) cotransport system rather than a K(+)/H(+) antiporter.

Journal Article↗
PubMed1987

Influence of mannose on the apoplasmic retrieval systems of source leaves.

Experiments were conducted in which d-mannose was supplied to mature Beta vulgaris L. (sugar beet) leaves, via the transpiration stream, to perturb photosynthetic carbon allocation by sequestering cytosolic Pi. Biochemical and enzymic analyses conducted on this tissue indicated that mannose 6-P was present, that it was only slowly metabolized, and that after a 24-hour pretreatment sugar metabolism was slightly perturbed. However, sucrose retrieval by the mesophyll tissue was greatly impaired in 24-hour mannose-pretreated tissue, a response which was due in part to mannose acting as an osmoticum. Inhibition of glucose, fructose, and arginine uptake into mannose-treated sugar beet leaf discs indicated that mannose may elicit a general perturbation of all membrane transport processes. This conclusion was supported by our finding that sucrose efflux was increased from mannose-treated tissue. Analysis of adenine nucleotide levels showed that whereas these levels declined over the first 3 to 6 hours of the mannose treatment, by 24 hours they had recovered to near control values. Similar experiments conducted on Nicotiana rustica indicated that whereas mannose 6-P was present in mature leaves, it remained at a much lower level than that found in sugar beet. Sucrose uptake into N. rustica was insensitive to mannose pretreatment. However, glucosamine treatment, which is also thought to sequester cytosolic Pi, inhibited sucrose uptake in both N. rustica and B. vulgaris. Further, experiments conducted on N. tabacum L. var Xanthii showed that mannose caused an inhibition of sucrose uptake, indicating that a range of sensitivity to mannose exists between closely related species. These results are discussed in terms of possible mechanisms of inhibition.

Journal Article↗
PubMed1986

Ion transport and the vibrating probe.

The theory of ion transport in the vicinity of a vibrating probe is developed. It is shown that the convection loops produced by the probe will not affect the electrical current density, assuming that the action of the probe does not affect the sources of the current in the biological system. However, the convection loops will significantly alter the ion concentration gradients in the unstirred layer near a tissue or cell surface. The concentration gradients within each convection loop will be reduced, while the concentration gradients between the loops and outside of the loops will be increased relative to the gradients existing without the probe. As a consequence, the electrical potential gradients can be changed relative to the potential gradients existing in the absence of the convection caused by the probe. If the mobility of the ion species carrying the electrical current is greater than the average ion mobility in the medium, then a decrease in ion concentration gradient will be accompanied by an increase in electrical potential gradient, while an increase in concentration gradient will be accompanied by a decrease or even a reversal of electrical potential gradient. Thus, the electrical potential gradient measured by the probe will depend on the concentration gradient in the vicinity of the probe, which will depend in turn on the spatial relation of the convection loops to the probe. An example of the effect of the convection loops on ion concentration and electrical potential is obtained from the theory via a numerical computer calculation. Experimental tests of this theory are discussed.

Biological Transport↗
PubMed1986

(1-->3)-beta-d-Glucan Synthase from Sugar Beet : I. Isolation and Solubilization.

A (1-->3)-beta-glucan synthase has been isolated from petiole tissue of sugar beet (Beta vulgaris L.). Enzyme activity is associated with a membrane fraction with a density of 1.03 grams per cubic centimeter when subjected to isopycnic density gradient centrifugation in Percoll. The reaction product was determined to be a linear (1-->3)-beta-glucan by methylation analysis and by glucanase digestion. (1-->3)-beta-Glucan synthase activity is markedly stimulated by Ca(2+); activation is half-maximal at about 50 micromolar Ca(2+) and is nearly saturated at 100 micromolar. Other divalent cations tested, Mg(2+), Mn(2+), and Sr(2+), also stimulate enzyme activity but are less effective. Enzyme activity was also stimulated up to 12-fold by beta-glucosides. Sirofluor, the fluorochrome from aniline blue, inhibited enzyme activity 95% when included at 1 millimolar. The enzyme was solubilized in Zwittergent 3-14; 85% of total enzyme activity was solubilized in 0.03% detergent and the optimal detergent-to-protein ratio was 0.3 at 3 milligrams per milliliter protein.

Journal Article↗
PubMed1986

Symplastic Transport in Ipomea tricolor Source Leaves : Demonstration of Functional Symplastic Connections from Mesophyll to Minor Veins by a Novel Dye-Tracer Method.

A novel method for the delivery of the fluorescent dye Lucifer Yellow CH to the cytosol of a source leaf mesophyll cell was devised which utilized a preencapsulation of the dye in phospholipid vesicles (liposomes). The liposomes were easily injected into the vacuoles of leaf cells of Beta vulgaris or Ipomea tricolor, where fusion with the tonoplast resulted in the release of the dye into the cytosol. Subsequent cell-to-cell movement of the dye was readily followed by fluorescence microscopy. Using this liposome technique symplastic continuity from the the mesophyll to the minor veins of the source leaf of Ipomea tricolor was demonstrated. This agreed with ultrastructural studies which demonstrated the presence of plasmodesmata between all cells from the mesophyll to the minor veins. The symplastic movement of dye from the injected mesophyll cell to the minor veins was unaffected by pretreatment of the leaf tissues with 2 millimolar p-chloromercuribenzenesulfonic acid. Pretreatment of the leaf tissues at alkaline pH (3-[N-morpholino] propanesulfonic acid-KOH, pH 8.0) had no apparent effect on dye movement between adjacent mesophyll cells but inhibited the movement of dye into and along the minor veins. Thus, although there were no apparent barriers to symplastic solute movement in this leaf, symplastic barriers could be imposed by the experimental conditions used.

Journal Article↗
PubMed1986

Spectrophotometric and cytochemical analyses of phosphatase activity in Beta vulgaris L.

Spectrophotometric and cytochemical methods were used to investigate the localization and/or the sensitivity of phosphatase activities in aldehyde-fixed beet leaves and membrane fractions. The nonspecific acid phosphatase substrates, p-nitrophenyl phosphate and beta-glycerol phosphate, each exhibited unique spectrophotometric patterns of hydrolysis as a function of pH. Additionally, beta-glycerol phosphatase activity was primarily present on the tonoplast, whereas p-nitrophenyl phosphatase was present on the plasma membrane. Because of the unique pH response of each enzyme and their different localization, we conclude that they cannot be entirely "nonspecific." The spectrophotometric pattern of ATP hydrolysis differed from that of p-nitrophenol phosphate in that it decreased at pH 5.0-5.5 and was greatly inhibited by 10 mM sodium fluoride; however, both activities were on the plasma membrane. Therefore, we conclude that these activities represent either two enzymes or only one enzyme that differs in its ability to hydrolyze these two substrates. Generally, enzymatically produced lead deposits on the plasma membrane of non-vascular cells were as frequent and large as those on phloem cells; frequently, deposits on sieve element plasma membranes were relatively small. We therefore conclude that there is no evidence for the presence of relatively intense ATPase activity on the plasma membrane of phloem cells in beet leaf, in contrast to other species. Studies with membrane fractions indicated that formaldehyde could completely inhibit the inhibitor-sensitive phosphatase activities in mitochondrial and vacuolar fractions while preserving significant activity in the plasma membrane fraction.

Adenosine Triphosphatases↗
PubMed1985

Potassium Transport in Corn Roots : III. Perturbation by Exogenous NADH and Ferricyanide.

It has recently been reported that plasmalemma electron transport may be involved in the generation of H(+) gradients and the uptake of ions into root tissue. We report here on the influence of extracellular NADH and ferricyanide on K(+) ((86)Rb(+)) influx, K(+) ((86)Rb(+)) efflux, net apparent H(+) efflux, and O(2) consumption in 2-centimeter corn (Zea mays [A632 x Oh43]) root segments and intact corn roots. In freshly excised root segments, NADH had no effect on O(2) consumption and K(+) uptake. However, after the root segments were given a 4-hour wash in aerated salt solution, NADH elicited a moderate stimulation in O(2) consumption but caused a dramatic inhibition of K(+) influx. Moreover, net apparent H(+) efflux was significantly inhibited following NADH exposure in 4-hour washed root segments.Exogenous ferricyanide inhibited K(+) influx in a similar fashion to that caused by NADH, but caused a moderate stimulation of net H(+) efflux. Additionally, both reagents substantially altered K(+) efflux at both the plasmalemma and tonoplast.These complex results do not lend themselves to straightforward interpretation and are in contradiction with previously published results. They suggest that the interaction between cell surface redox reactions and membrane transport are more complex than previously considered. Indeed, more than one electron transport system may operate in the plasmalemma to influence, or regulate, a number of transport functions and other cellular processes. The results presented here suggest that plasmalemma redox reactions may be involved in the regulation of ion uptake and the ;wound response' exhibited by corn roots.

Journal Article↗
PubMed1985

Potassium Transport in Corn Roots : IV. Characterization of the Linear Component.

A detailed examination was conducted on the linear, or first-order kinetic component for K(+)((86)Rb(+)) influx into root segments of both low- and high-salt grown corn seedlings (Zea mays [A632 x Oh 43]). In tissue from both low- and high-salt grown roots, replacement of Cl(-) in the uptake solution by either SO(4) (2-), H(2)PO(4) (-), or NO(3) (-) caused a significant (50-60%) and specific inhibition of the linear component of K(+) influx. The anion transport inhibitor, 4,4'-diisothiocyano-2,2'-disulfonic acid, was found to abolish saturable Cl(-) influx in corn roots while causing a significant (50-60%) and specific inhibition of the linear K(+) uptake system; this inhibition was identical to that observed when Cl(-) was replaced by other anions in the K(+) uptake solution. Additionally, the quaternary ammonium cation, tetraethylammonium, which has been shown to block K(+) channels in nerve axons, also caused a dramatic (70%) and specific inhibition of the linear component of K(+) influx, but this was obtained only in high-salt roots. The reasons for this difference are discussed with respect to the differing abilities of low- and high-salt roots to absorb tetraethylammonium.Our present results indicate that the linear component of K(+) influx may occur by a passive process involving transmembrane K(+) channels. Fluxes through these K(+) channels may be partly coupled to a saturating Cl(-) influx mechanism.

Journal Article↗
PubMed1984

Plasma membrane coat and a coated vesicle-associated reticulum of membranes: their structure and possible interrelationship in Chara corallina.

Primary fixation with buffered glutaraldehyde plus 2.0 mM CaCl2 and 0.1% tannic acid results in the preservation of certain portions of the plasma membrane coat of Chara when seen with the electron microscope. Such a coat is not observable after fixation with glutaraldehyde alone. The coat appears to be present on all the above ground, vegetative cells of the male plant. Within complex invaginations of the plasma membrane, which are known as charasomes, the coat has two structural components, a central core that is either tubular or solid and a fibrous or granular peripheral region that surrounds the core. The coat material appears to be at least partially derived, via exocytosis, from the contents of single membrane-bound organelles known as glycosomes. Glycosomes seem to originate from within an assemblage of membranes and coated vesicles that can be described, in purely structural terms, as a partially coated reticulum. Such a reticulum is distinguishable from Golgi stacks because the reticulum (a) is not composed of stacked membranes, (b) is extensively involved with large, clearly detailed coated vesicles and coated invaginations, (c) is closely associated with glycosomes, and (d) is only slightly stained by the zinc-iodide-osmium tetraoxide reagent.

Calcium Chloride↗
PubMed1984

Perturbation of Chara Plasmalemma Transport Function by 2[4(2',4'-Dichlorophenoxy)phenoxy]propionic Acid.

Electrophysiological measurements on internodal cells of Chara corallina Klein ex Willd., em. R.D.W. revealed that in the presence of (2-[4-(2',4'-dichlorophenoxy)phenoxy]propionic acid) (diclofop) the membrane potential was very sensitive to the pH of the bathing medium. At pH 5.7, 100 micromolar diclofop caused a slow reduction in the electrogenic component of the membrane potential to the value of -123 +/- 5 millivolts. Membrane resistance initially decreased, recovered transiently, then stabilized at approximately 65% of the control value. At pH 7.0, the potential appeared to plateau around -200 millivolts before rapidly declining to -140 +/- 4 millivolts; removal of diclofop resulted in recovery of the electrogenic component. Diclofop reduced cytoplasmic ATP levels by 96.4% and 36.6% at pH 5.7 and 7.0, respectively. At pH 8.2, diclofop did not change the ATP concentration significantly, but induced a hyperpolarization of the membrane potential to near -250 millivolts, and also reduced or inhibited the dark-induced hyperpolarization; the light-induced depolarization was reduced to a lesser extent. DCMU applied in the light elicited the same response at the plasmalemma as placing cells in the dark. When K(+) channels were opened and cells depolarized with 10 millimolar K(+), diclofop induced a further depolarization of approximately 30 millivolts. Cells decoupled with HPO(4) (-2) were still sensitive to diclofop. Currents associated with OH(-) efflux and HCO(3) (-) influx, as measured with a vibrating probe technique, became spatially destabilized and reduced in magnitude in the presence of diclofop. After 60 minutes, most of the cell surface was engaged in a low level of OH(-) efflux activity. The results indicate that diclofop may be a proton ionophore at pH 7.0 and 5.7. At pH 8.2, diclofop may inhibit the operation of the H(+)-ATPase and OH(-) efflux systems associated with HCO(3) (-) transport by perturbing the control processes that integrate the two, without a reduction in ATP concentration.

Journal Article↗
PubMed1983

Potassium Transport in Corn Roots : II. The Significance of the Root Periphery.

The relative transport capabilities of the cells of the root periphery and cortex were investigated using a variety of experimental techniques. Brief (30 seconds to 1 minute) exposures with the penetrating sulfhydryl reagent, N-ethyl maleimide (NEM), and the impermeant reagent, p-chloromercuribenzene sulfonic acid (PCMBS), dramatically reduced (86)Rb(+) (0.2 millimolar RbCl) uptake into 2 centimeter corn (Zea mays [A632 x (C3640 x Oh43)]) root segments. Autoradiographic localization studies with [(3)H]NEM and [(203)Hg]PCMBS demonstrated that, during short term exposures with either reagent, sulfhydryl binding occurred almost exclusively in the cells of the root periphery.Corn root cortical protoplasts were isolated, and exhibited significant K(+)((86)Rb(+)) influx. The kinetics for K(+) uptake were studied; the influx isotherms were smooth, nonsaturating curves that approached linearity at higher K(+)(Rb(+)) concentrations (above 1 millimolar K(+)). These kinetics were identical in shape to the complex kinetics previously observed for K(+) uptake in corn roots (Kochian, Lucas 1982 Plant Physiol 70: 1723-1731), and could be resolved into a saturable and a first order kinetic component.The existence of a hypodermal apoplastic barrier was investigated. The apoplastic, cell wall binding dye, Calcofluor White M2R, appeared to be excluded from the cortex by the hypodermis. However, experiments with damaged roots indicated that this result may be an artifact resulting from the binding of dye to the epidermal cell walls. Furthermore, [(203)Hg] PCMBS autoradiography demonstrated that the hypodermis was not a barrier to apoplastic movement of PCMBS.These results suggest that although cortical cells possess the capacity to absorb ions, K(+) influx at low concentrations is limited to the root periphery. Cortical cell uptake appears to be repressed under these conditions. At higher concentrations, cortical cells may function to absorb K(+). Such a model may involve regulation of cortical cell ion transport capacity.

Journal Article↗
PubMed1982

A Reanalysis of the Two-Component Phloem Loading System in Beta vulgaris.

Kinetic analysis of [(14)C]sucrose loading into sugar beet leaf discs revealed the presence of two transport components. At low exogenous sucrose concentrations, a saturable component, which exhibited Michaelis-Menten characteristics, was the main mode of transport. At concentrations greater than 50 millimolar, phloem loading was dominated by a linear component which appeared to operate as a first order kinetic transport process. Over the exogenous sucrose concentrations employed, influx could be described by the equation v = V(max)S/(S + K(m)) + kS. Influx via both processes was strongly pH-dependent. Evidence is presented that the linear component was not explicable in terms of simple diffusion, or exchange diffusion, into either mesophyll or minor vein phloem tissue. Extensive metabolic conversion of sucrose was not a factor contributing to influx at high external sucrose concentrations. At present, it is believed that both components operate in parallel at the membrane bounding the sieve element-companion cell complex. The saturable component is identified with sucrose-H(+) cotransport. While the significance of the linear component has been established, its nature remains to be elucidated.

Journal Article↗
PubMed1982

Potassium Channels in Chara corallina: CONTROL AND INTERACTION WITH THE ELECTROGENIC H PUMP.

Plasmalemma electrical properties were used to investigate K(+) transport and its control in internodal cells of Chara corallina Klein ex Willd., em R.D.W. Cell exposure to solutions containing 10 mm KCl caused the potential, normally -250 millivolts (average), to depolarize in two steps. The first step was a 21 millivolt depolarization that lasted from 1 to 40 minutes. The second step started with an action potential and left the membrane potential at -91 millivolts, with a 10-fold reduction in resistance. We suggest that the second step was caused by the opening of K(+) -channels in the membrane. This lowered the resistance and provided a current pathway that partially short-circuited the electrogenic pump. Although largely short-circuited, the electrogenic pump was still operating as indicated by: (a) the depolarized potential of -91 millivolts was more negative than Ek (=-42 millivolts in 10 mm K(+)); (b) a large net K(+) uptake occurred while the cell was depolarized; (c) both the electrogenic pump inhibitor, diethylstilbestrol, and the sulfhydryl-reagent N-ethylmaleimide (which increased the passive membrane permeability) further depolarized the potential in 10 mm KCl.A two-phase recovery back to normal cell potentials occurred upon lowering the K(+) concentration from 10 to 0.2 mm. The first phase was an apparent Nernst potential response to the change in external K(+) concentration. The second phase was a sudden hyperpolarization accompanied by a large increase in membrane resistance. We attribute the second phase to the closing of K(+) -channels and the removal of the associated short-circuiting effect on the electrogenic pump, thereby allowing the membrane to hyperpolarize. Further experiments indicated that the K(+) -channel required Ca(2+) for normal closure, but other ions could substitute, including: Na(+), tetraethylammonium, and 2,4,6-triaminopyrimidine. Apparently, K(+) -channel conductance is determined by competition between Ca(2+) and K(+) for a control (gating?) binding site.

Journal Article↗
PubMed1982

Plasmalemma Chloride Transport in Chara corallina: Inhibition by 4,4'-Diisothiocyano-2,2'-Disulfonic Acid Stilbene.

Chloride transport, presumably via a Cl(-)-2H(+) co-transport system, was investigated in Chara corallina. At pH 6.5, the control influx (3.1 picomoles per centimeter(2) per second) was stimulated 4-fold by an 18-hour Cl(-) starvation. The stimulated influx was inhibited to 4.7 picomoles per centimeter(2) per second after a 60-minute pre-exposure to 0.5 millimolar 4,4'-diisothiocyano-2,2'-disulfonic acid stilbene (DIDS). This compares with a nonsignificant inhibition of the control under similar conditions. At 2 millimolar DIDS, both stimulated and control influx were inhibited to values of 1.1 and 2.2 picomoles per centimeter(2) per second, respectively; in all cases, DIDS inhibition was reversible. Over the pH range 4.8 to 8.5, the control and DIDS-inhibited influx showed only slight pH sensitivity; in contrast, the stimulated flux was strongly pH dependent (pH 6.5 optimum). Inasmuch as changes in pH alter membrane potential, N-ethylmaleimide was used to depolarize the membrane; this had no effect on Cl(-) influx. A transient depolarization of the membrane (about 20 millivolts) was observed on restoration of Cl(-) to starved cells. The membrane also depolarized transiently when starved cells were exposed to 0.5 millimolar DIDS, but the depolarization associated with Cl(-) restoration was inhibited by a 40-minute pretreatment with DIDS. Exposure of control cells to DIDS caused only a small hyperpolarization (about 7 millivolts). DIDS may have blocked Cl(-) influx by inhibiting the putative plasmalemma H(+)-translocating ATPase. Histochemical studies on intact cells revealed no observable effect of DIDS on plasmalemma ATPase activity. However, DIDS application after fixation resulted in complete inhibition of ATPase activity.The differential sensitivity of the stimulated and control flux to inhibition by DIDS may reflect an alteration of transport upon stimulation, but could also result from differences in pretreatment. The stimulated cells were pretreated with DIDS in the absence of Cl(-), in contrast to the presence of Cl(-) during pretreatment of controls. The differential effect could result from competition between Cl(-) and DIDS for a common binding site. Our histochemical ATPase results indicate that Cl(-) transport and membrane ATPase are separate systems, and the latter is only inhibited by DIDS from the inside of the cell.

Journal Article↗
PubMed1982

Sucrose and Glucose Uptake into Beta vulgaris Leaf Tissues : A Case for General (Apoplastic) Retrieval Systems.

Concentration curves for sugar and amino acid uptake by Beta vulgaris L. leaf tissues contained both a saturable and a linear component. Similarly shaped curves were obtained for influx of sucrose, glucose, and 3-O-methyl glucose by leaf discs, whole petiole slices, petiole segments containing pith tissue only, and petiole segments containing vascular bundles, although the tissues took up the various sugars via different proportions of saturable versus linear uptake. Two millimolar p-chloromercuribenzenesulfonic acid selectively inhibited the saturable component of sucrose uptake, but had almost no effect on the linear component. Uptake of glucose and 3-O-methyl glucose remained unaffected by p-chloromercuribenzenesulfonic acid treatment. Anoxia was found to inhibit the linear component of both sucrose and 3-O-methyl glucose influx, while the saturable component remained unaffected. The linear component of sucrose uptake was also competitively inhibited by maltose, as well as being selectively promoted by certain exposures to 5 millimolar N-ethylmaleimide, 2 micrograms per milliliter cycloheximide, and high levels of mannitol acting as osmoticum. These results support the proposal that the linear component is due to a process more complex than simple, or exchange, diffusion. It would also appear that the linear transport component utilizes a separate energy source than does the saturable component of sucrose influx.Evidence for phloem loading from the apoplast was re-examined with respect to the present findings. Saturable sucrose uptake by minor vein tissues may represent retrieval of solute from the free space, which could explain the ;apoplastic loading' phenomenon.

Journal Article↗
PubMed1982

Potassium transport in corn roots : I. Resolution of kinetics into a saturable and linear component.

Influx isotherms were obtained for (86)Rb(+) uptake into 2-cm corn (Zea mays [A632 x (C3640 x Oh43)] root segments for both low- (0.2 millimolar CaSO(4)) and high-salt (0.2 millimolar CaSO(4) + 5 millimolar KCl) grown roots. Unlike the discontinuous curves usually presented for K(+) influx, our isotherms were smooth, nonsaturating curves that approached linearity at K(+) (Rb(+)) concentrations above 1 millimolar. The kinetics for K(+) transport could be resolved into saturable and linear components. The saturable components yielded K(m) values of 16 and 86 micromolar for low- and high-salt roots, respectively, while V(max) values were 5.62 and 1.85 moles per gram fresh weight per hour. Results of experiments with the penetrating sulfhydryl reagent, N-ethyl maleimide (NEM), and the impermeant reagent, p-chloromercuribenzene sulfonic acid (PCMBS) indicated that the saturable and linear components were independent mechanisms of K(+) transport.Short-term NEM exposures (30 seconds to 5 minutes) selectively inhibited the saturable system, but had little effect on the linear component. Increasing NEM exposures resulted in further inhibition and subsequent abolition of the saturable component; the linear component exhibited limited NEM sensitivity. PCMBS elicited the same general inhibitory trends, although it was less effective as a saturable component inhibitor.The effects of NEM and PCMBS on K(+) efflux were also studied. Short NEM exposures had no effect on cytoplasmic efflux, while inhibiting vacuolar efflux significantly. From these data, it is unclear at which site(s) NEM is acting. A more complex response was obtained with PCMBS, where a monophasic efflux curve was observed. Analysis indicated that the vacuolar efflux was stimulated, while the cytoplasmic component was abolished.The nature of the linear component is discussed, and it is proposed that the mechanism may be more complex than simple facilitated diffusion.

Journal Article↗