Cotransport Process Research Articles

Mechanistic insights into the co-transport of microplastic degradation products in saturated porous media: The key role of microplastics-derived DOM

Microplastic-derived dissolved organic matter (MP-DOM) forms from the aging of microplastics (MPs), but the co-transport behavior of MP-DOM and aged MPs (AMPs) remains poorly understood. This study investigates the co-transport of AMPs and MP-DOM generated from original MPs (OMPs) over a wide range of environmentally relevant conditions. The transport of AMPs and MP-DOM changes as the degree of aging increases, specifically related to changes in their physicochemical characteristics. Results showed that the order of migration ability was MP-DOM > AMPs > OMPs under almost all tested conditions. The change of hydrophobicity of MP-DOM and AMPs, as well as small molecular weight of MP-DOM, was primarily responsible for this order. The role of MP-DOM as a degradation product in the co-transport process is notably significant under various environmental conditions because of its high mobility and organic carbon fraction within the system. Furthermore, it is important to note that MP-DOM affected the transport of MPs through a combination of positive and negative effects. Key mechanisms include electrostatic repulsion caused by protonation reactions triggered by the acidic pH of MP-DOM, steric hindrance, and competition for retention sites on media surfaces. This study contributes to a deeper understanding of the transformation and fate of MPs in complex environmental systems.

Interaction between Microplastics and Pathogens in Subsurface System: What We Know So Far

Microplastics (MPs) are abundant in soil and the subsurface environment. They can co-transport with pathogens or act as vectors for pathogens, potentially causing severe ecological harm. The interaction of MPs with pathogens is an important topic. To describe the origins and features of MPs in the subsurface environment, we evaluated relevant studies conducted in the laboratory and field groundwater habitats. We explore the interactions between pathogens and microplastics from three perspectives including the respective physicochemical properties of microplastics and pathogens, external environmental factors, and the binding between microplastics and pathogens. The effects of some interaction mechanisms and environmental factors on their co-transport are discussed. The key factors affecting their interaction are the particle size, specific surface area, shape and functional groups of MPs, the zeta potential and auxiliary metabolic genes of pathogens, and the hydrophobicity of both. Environmental factors indirectly affect MPs and the interaction and co-transport process of pathogens by changing their surface properties. These findings advance our knowledge of the ecological behavior of MPs–pathogens and the associated potential health hazards.

Interplay of compound pollutants with microplastics transported in saturated porous media: Effect of co-existing graphene oxide and tetracycline

Co-existence of microplastics, nanomaterials, and antibiotics may lead to intensified multifaceted pollution, which may influence their fate in soils. This study investigated the co-transport behavior of polystyrene microplastics (PS) and compound pollutants of graphene oxide (GO) and tetracycline (TC). Packed column experiments for microplastic with or without combined pollutants were performed in KCl (10 and 30 mM) and CaCl2 solutions (0.3 and 1 mM). The results showed transport of PS was facilitated at low ionic strengths and inhibited at high ionic strengths by GO with or without TC under examined conditions. Carrier effect of GO as well as the aggregation of PS in the presence of co-exiting GO or GO-TC could be the contributor. Although the existence of TC relieved the ripening phenomenon of PS and GO deposition due to enhanced electronegativity of sand media, the effect of GO on the PS transport has not been significantly impacted, indicating the dominant role of GO during cotransport process. Furthermore, the transport of PS was increased by TC owing to competition for deposition sites on sand surfaces. In turn, the transport of TC was mainly affected by PS whether graphene was present or not. The increase in electrostatic repulsive force (transport-promoting) and addition adsorption sites (transport-inhibiting) may be responsible for the observations. Our findings could improve understandings of complex environmental behaviors of microplastics and provide insight into investigation on cotransport of emerging contaminants under various conditions relevant to the subsurface environment.

Effects of ionic strength and particle size on transport of microplastic and humic acid in porous media

As an emerging pollutant, the transport behavior of colloidal microplastic particles (CMPs) in saturated porous media may be affected by the simultaneous presence of other substances in the natural environment. In this study, colloidal polystyrene microplastic particles (PSMPs) were selected as the representative of CMPs to investigate the cotransport behaviors of CMPs in the presence of humic acid (HA) under varied environmental conditions (ionic strength: 1, 100 mM KCl; HA concentration: 0, 5, 10, 20 mg⋅L−1) in porous media. The presence of HA with different concentrations was found to increase the mobility of 1.0-μm and 0.2-μm CMPs in porous media in a non-linear and non-monotonic manner. Furthermore, the HA-facilitated transport of CMPs occurred under both electrostatically unfavorable and favorable attachment conditions (limited to the conditions examined in this study, corresponding to 1 and 100 mM KCl, respectively). The transport behavior of the smaller-sized CMPs (0.2-μm CMPs) was more sensitive to the change of ionic strength and the presence of HA than that of the larger-sized CMPs (1.0-μm CMPs). The cotransport process of CMPs and HA was affected by many factors. Modeling results showed that a small amount of competitive blocking occurred during the cotransport process. Moreover, both the presence of HA and change in ionic strength could affect the surface properties of CMPs. Thus, the cotransport behavior of CMPs with HA was different from the transport of individual CMPs in porous media. Experimental results revealed that HA induced complexity in the transport behavior of CMPs in the aqueous environment. Therefore, undeniably, a lot more systematic explorations are further demanded to better comprehend the CMPs cotransport mechanism in the presence of other substances.

Effects of the same valence metal cations on the aggregation behavior of PFR

In recent years, phenol-formaldehyde resin (PFR) as a colloid plugging agent was extensively used in enhanced oil recovery. It has been popularly concerned that the influence of environment on the structure, migration and aggregation behavior of PFR. The classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory can explain the interaction potential between particles. However, the classical DLVO cannot explain differences when colloids aggregate in the same valence metal cation solution. In this work, the effects of ion specificity of divalent metal cations (i. e., Mg2 + and Ca2 +) on the aggregation rate, fractal dimension, zeta potential and the critical coagulation concentration (CCC) of PFR were systematically studied by dynamic light scattering experiment, electrophoretic light scattering and spectral turbidimetry. The experimental results showed that metal cations with poor hydration (i. e., Mg2 +) can promote aggregation more than metal cations with good hydration (i. e., Ca2 +). The hydrated differences of ions can be explained quantitatively by the improved DLVO theory introducing Lewis acid-base interaction. This result revealed the important significance of ion specificity in the aggregation behavior of PFR colloids, and made it possible to understand the co-transport process of PFR aggregates and metal cations in reservoirs. Thus, it is possible to precisely control the aggregation rate and the fractal dimension of PFR aggregates.

Equilibrium properties of E. coli lactose permease symport-A random-walk model approach.

The symport of lactose and H+ is an important physiological process in E. coli, for it is closely related to cellular energy supply. In this paper, we review, extend and analyse a newly proposed cotransport model that takes the “leakage” phenomenon (uncoupled particle translocation) into account and also satisfies the static head equilibrium condition. Then, we use the model to study the equilibrium properties, including equilibrium solution and the time required to reach equilibrium, of the symport process of E. coli LacY protein, when varying the parameters of the initial state of cotransport system. It can be found that in our extended model, H+ and lactose will reach their equilibrium state separately, and when “leakage” exists, it linearly affects the equilibrium solution, which is a useful property that the original model does not have. We later investigated the effect of the volume of periplasm and cytoplasm on the equilibrium properties. For a certain E. coli cell, as it continues to lose water and contract, the time for cytoplasm pH to be stabilized by symport increases monotonically when the cell survives. Finally, we reproduce the experimental data from a literature to verify the validity of the extension in this symport process. The above phenomena and other findings in this paper may help us to not only further validate or improve the model, but also deepen our understanding of the cotransport process of E. coli LacY protein.

Impact of rice straw biochar addition on the sorption and leaching of phenylurea herbicides in saturated sand column

The application of phenylurea herbicides (PUHs) may lead to the extensive distribution in soils, while the role of straw biochar as a soil amendment on the transport and sorption of PUHs are still unclear. Thus, the transport and sorption behavior of three typical PUHs with rice straw biochar (RSB) was studied in both adsorption simulation experiments of aqueous solution and packed column experiments. The sorption mechanism of RSB to herbicides was investigated through batch sorption studies with three influencing factors including dosage of RSB, pH, and ionic strength (IS) with orthogonal test. The sorption coefficients were improved significantly by increasing the dosage of RSB, while there was no obvious influence by enhancing the pH and IS value. The optimal sorption conditions (pH value at 3, IS at 0.1 M, and RSB dosage at 60 mg) of three herbicides were set and the maximum removal rates of Monuron, Diuron, and Linuron were 41.9%, 25%, and 56.8%, respectively. The co-transport process of RSB and PUHs were investigated under different RSB dosage, pH value, and IS value. The retention effect increased greatly with enhancing the RSB dosage and pH value. However, IS did not have a significant influence on the retention of RSB, and therefore it had little effect on the adsorption capacity, which was consistent with the results of sorption experiments. The breakthrough curves (BTCs) for co-transport were well simulated by the two-site non-equilibrium convection–dispersion equation (CDE). Most of the regression coefficients (R2) were above 0.99, which uncovered the co-transport in packed column were affected by physical absorption and chemical forces. According to the fitting parameters analysis, the RSB particles and PUHs were subjected to a greater resistance and a stronger stability by reducing pH value in porous media. The presence of RSB increased the amount of dynamic sorption sites in the entire co-transport system, which led to a significant promotion of the PUHs' sorption and interception.

Tris-ureas as transmembrane anion transporters.

Nine tris-urea receptors (L(1)-L(9)) have been synthesised and shown to coordinate to a range of anionic guests both by (1)H NMR titration techniques and single crystal X-ray structural analysis. The compounds have been shown to be capable of mediating the exchange of chloride and nitrate and also chloride and bicarbonate across POPC or POPC : cholesterol 7 : 3 vesicle bilayer membranes at low transporter loadings. An interesting dependency of anion transport on the nature of the cation is evidence to suggest that a M(+)/Cl(-) cotransport process may also contribute to the release of chloride from the vesicles.

Glucose transport into everted sacs of the small intestine of mice

The Na(+)-glucose cotransporter is a key transport protein that is responsible for absorbing Na(+) and glucose from the luminal contents of the small intestine and reabsorption by the proximal straight tubule of the nephron. Robert K. Crane originally described the cellular model of absorption of Na(+) and glucose by a "cotransport process" in 1960. Over the past 50+ yr, numerous groups have tested and verified Crane's hypothesis. Eventually, Wright and colleagues cloned the Na(+)-glucose cotransporter (SGLT1; the product of the SLC5A1 gene) in 1987. This article provides a "hands-on" laboratory exercise using the everted mouse jejunal preparation (everted sac) that allows students to investigate various components of the Na(+)-glucose cotransport absorptive cell model (e.g., Na(+) dependence of SGLT1, inhibition of SGLT1, and inhibition of Na(+)-K(+)-ATPase). Additionally, the laboratory exercise includes a case-based study of glucose-galactose malabsorption in which the students conduct an internet search and participate in a small-group discussion during the laboratory period to better understand the basic principles and functions of the Na(+)-glucose absorptive process of the small intestine. This laboratory exercise was introduced into the second-year undergraduate physiology curriculum in 2008, and >850 physiology students have participated in this laboratory exercise. The students have produced very robust and reproducible data that clearly illustrate the theory of the cellular model for Na(+)-glucose absorption by the jejunum.

Stimulation of phosphorus uptake by ammonium nutrition involves plasma membrane H+ ATPase in rice roots

Aims Nitrogen, especially NH 4 + , can stimulate the uptake of phosphorus in plants, but the underlying mechanisms have not been clearly elucidated. Because phosphate is taken up via an anion/H+ co-transport process, we propose that the stimulated uptake of phosphorus by NH 4 + versus NO 3 - nutrition may be related to the activity of plasma membrane H+ ATPase. In the present study, we investigated the effect of NH 4 + and NO 3 - on phosphorus uptake and plasma membrane H+ ATPase activity in rice.

IR Spectroscopic Observation of Molecular Transport through Pt@CoO Yolk−Shell Nanostructures

FTIR spectroscopy has been used to monitor the transport of CO to the Pt cores of Pt@CoO nanoparticles forming CO/Pt species. It was found that external Pt sites are not present on the outer surfaces of the approximately 10 nm diameter nanostructures and that CO transports to Pt adsorption sites by an activated surface diffusion process through the CoO shells surrounding approximately 2 nm diameter Pt cores. The CO transport process is not due to gas-phase transport below 300 K. The weakly bound adsorbed CO/CoO species responsible for transport was directly observed at approximately 2147 cm(-1) during transport through the CoO shells.

The ins and outs of tRNA transport

Transfer RNAs (tRNAs) are involved in many cellular functions distributed throughout the cellular space. In addition to their role in protein translation, these molecules are engaged in tasks as diverse as the regulation of gene expression, amino‐acid synthesis, protein degradation, cell‐wall synthesis, porphyrin biosynthesis, priming of replication, RNA interference and the transport of macromolecules. The nucleus and the mitochondria of eukaryotic cells, as well as the chloroplasts in plants, contain their own genome that encodes a range of proteins and nucleic acids. Early evidence suggested that some of the RNA content of mitochondria could be transcribed from non‐mitochondrial DNA (Suyama, 1967). It is now well established that a variable number of tRNA species present in the mitochondria are indeed nucleus‐encoded (Fig 1). The phenomenon of mitochondrial tRNA import has been reported in plants, marsupials, the yeast Saccharomyces cerevisiae , and the protozoa Leishmania , Trypanosoma and Tetrahymena . When certain tRNA species are not encoded by the mitochondrial genome, there is a predictable requirement for the import of nucleus‐encoded tRNAs into the mitochondria (Schneider & Marechal‐Drouard, 2000). This is the case, for example, for the mitochondria of Leishmania , which are completely devoid of tRNA‐encoding genes. However, there are a few examples of tRNA import into mitochondria that already have a complete set of mitochondria‐encoded tRNAs. Other tRNA transport systems have also been identified (Fig 1), which include their retrograde transport from the cytoplasm to the nucleus (Takano et al , 2005; Shaheen & Hopper, 2005), the export of mitochondria‐encoded tRNA to the cytoplasm (Maniataki & Mourelatos, 2005), and the packaging of tRNAs into retroviruses (Waters & Mullin, 1977). The roles of some of these transport systems have yet to be defined. Figure 1. The travels of transfer RNA. …

Transepithelial transport of zinc and l-histidine across perfused intestine of American lobster, Homarus americanus

The intestine of the American lobster, Homarus americanus, was isolated and perfused in vitro with a physiological saline, based on the ion composition of the blood, to characterize the mechanisms responsible for transmural transport of zinc and how the amino acid, L-histidine, affects the net movement of the metal across the tissue. Previous studies with this preparation, focusing on the characteristics of unidirectional mucosa to serosa (M to S) fluxes of (65)Zn(2+) and (3)H-L-histidine, indicated the presence of a brush border co-transport process responsible for simultaneously transferring the metal and amino acid across this tissue as an apparent bis-complex (Zn-[His](2)) using a PEPT-1-like dipeptide carrier mechanism. In addition, both zinc and L-histidine were also transferred toward the blood by separate transporters that were independent of the other substrate. The focus of the present study was to characterize the serosa to mucosa (S to M) flux of (65)Zn(2+) under a variety of conditions, and use these values in conjunction with those from the previous study, to assess the direction and magnitude of net metal movement across the tissue. Transmural S to M transport of (65)Zn(2+) was markedly reduced with the addition of the serosal inhibitors ouabain (32%), excess K(+) (25%), excess Ca(2+) (30%), Cu(2+) (38%), nifedipine (21%), and vanadate (53%). In contrast, this flux was markedly stimulated with the serosal addition of ATP (24%) and excess Na(+) (28%). These results suggest that S to M fluxes of zinc occurred by the combination of the basolateral Na/Ca exchanger (NCX), where zinc replaced calcium, and a basolateral nifedipine-sensitive calcium channel. Transmural M to S (65)Zn(2+) fluxes (5-100 microM) were threefold greater than S to M metal transport, and the addition of luminal L-histidine doubled the net M to S zinc flux over its rate in the absence of the amino acid. The results of this paper and those in its predecessor indicate that zinc transport by the lobster intestine is absorptive and significantly enhanced by luminal amino acids.

Co-Transport of Metal Complexes by the Green Mussel Perna viridis

We examined the uptake of ligand-bound metals (Cd and Zn) by the green mussel Perna viridis using defined artificial seawater. Different free ion concentrations (1 pM to 10 microM) in uptake solutions were created by adding different amounts of total metals (Cd 0.1 nM to 0.1 mM; Zn 0.5 nM to 0.05 mM) and ligands (EDTA, NTA, citric acid). Our results showed that Cd and Zn uptake could not be fully explained by the free Cd and Zn concentrations in the presence of different ligands, indicating that metal-ligand complexes were at least partially available for uptake by the mussels. Total Zn concentrations appeared to be a better predictor of metal uptake than the free Zn ion concentrations in the presence of different ligands. Uptake of lipophilic organic metal complexes was substantially greater than the hydrophilic metal complexes, even though the free ion concentration was comparable or lower. Moreover, the radiolabeled ligand compounds were directly accumulated by the mussels. The accumulation of metal complexes may explain the increased metal uptake with increasing ligand and total metal concentration, even though the free ion metal concentration was constant. Overall, our experimental results indicated that free metal ion cannot fully explain metal uptake since metal complex species were also available to the mussels to some extent, apparently through a co-transport process.

Na-glucose and Na-neutral amino acid cotransport are uniquely regulated by constitutive nitric oxide in rabbit small intestinal villus cells

Na-nutrient cotransport processes are not only important for the assimilation of essential nutrients but also for the absorption of Na in the mammalian small intestine. The effect of constitutive nitric oxide (cNO) on Na-glucose (SGLT-1) and Na-amino acid cotransport (NAcT) in the mammalian small intestine is unknown. Inhibition of cNO synthase with N(G)-nitro-l-arginine methyl ester (L-NAME) resulted in the inhibition of Na-stimulated (3)H-O-methyl-D-glucose uptake in villus cells. However, Na-stimulated alanine uptake was not affected in these cells. The L-NAME-induced reduction in SGLT-1 in villus cells was not secondary to an alteration in basolateral membrane Na-K-ATPase activity, which provides the favorable Na gradient for this cotransport process. In fact, SGLT-1 was inhibited in villus cell brush-border membrane (BBM) vesicles prepared from animals treated with L-NAME. Kinetic studies demonstrated that the mechanism of inhibition of SGLT-1 was secondary to a decrease in the affinity for glucose without a change in the maximal rate of uptake of glucose. Northern blot studies demonstrated no change in the mRNA levels of SGLT-1. Western blot studies demonstrated no significant change in the immunoreactive protein levels of SGLT-1 in ileal villus cell BBM from L-NAME-treated rabbits. These studies indicate that inhibition of cNO production inhibits SGLT-1 but not NAcT in the rabbit small intestine. Therefore, whereas cNO promotes Na-glucose cotransport, it does not affect NAcT in the mammalian small intestine.

Simulation of Non-Linear Flow Density in Transition State from the Mathematical Model of the Diffusion of Metal Anions Through a Flat Sheet Supported Liquid Membrane

A mathematical model is developed for the carrier facilitated transport of metal ions through a flat sheet support liquid membrane (FSSLM) in transition state from Fick's second law. From this model, and from Fick's first law, the flow density is derived as a non-linear concentration gradient. Both expressions, concentration and flow density, depend on the thickness of the membrane and on time. Since the rate constant plays an important role in the model, it is considered as the parameter that controls the system and an equation for it is obtained. This equation explains the velocity of the co-transport process. The proposed model takes into account the species co-transported together with the metal ions. An equation for the number of moles of this species is obtained as a function of the metal species. The concentration gradient of this species explains the behaviour of pH in the feed phase during the process. The model is tested against experimental data corresponding to the transport of metal anions in acidic solution and it is shown that the co-transport process is reproduced with high accuracy.

The kinetic mechanism of the glutamate-aspartate carrier in rat intestinal brush-border membrane vesicles: the role of potassium.

The sodium dependent transport system for L-glutamate and L-aspartate localized in the apical part of rat enterocytes has previously been kinetically characterized (Prezioso, G., and Scalera, V. (1996). Biochim. Biophys. Acta 1279, 144-148). In this paper the mechanism by which the potassium cation specifically activates the L-glutamate-sodium cotransport process is investigated. Potassium has been found to act as an activator when it is present inside the membrane vesicles, while its presence outside is ineffective, and the effect is saturable. The kinetic parameters with respect to sodium and glutamate have been compared in the presence and in the absence of the activator. The results indicate that the ordered sodium-sodium glutamate mechanism is not altered by potassium, and that the activation is probably exerted on both the rate determining steps of the transport process. It is proposed that (1) a specific binding site for potassium is present on the inside hydrophilic part of the membrane carrier, (2) the binding of the effector accelerates the intramembrane rearrangement steps of both the disodium glutamate-carrier complex and the free carrier, (3) the affinity of the carrier is lowered with respect to sodium whereas it is increased for glutamate, and (4) K+ antiport is not performed by this carrier.

Transport of niobium(V) through a TBP–Alamine 336 supported liquid membrane from chloride solutions

The transport of niobium(V) in chloride medium through a supported liquid membrane (SLM), using Alamine 336 and tributyl phosphate (TBP) as carriers, has been investigated. The work has been undertaken by first determining the liquid–liquid extraction distribution of niobium(V) between aqueous solution and different organic solutions. Optimum conditions for both extraction and stripping were established. The mixture of Alamine 336 and TBP provided the best extraction in high chloride medium, while low HCl concentration stripped the ion from the loaded organic phase. Transport experiments were carried out with a permeation cell having a continuous flow system and constant agitation. The study of the liquid membrane included the chemical conditions, i.e. carrier concentration and hydrochloric acid concentration in the feed solution. Maximum niobium recovery at 10% of Alamine 336 in TBP was obtained at HCl concentration between 6 and 7 mol/dm 3. The mechanism postulated is referred to a synergistic extraction of Nb(V) by means of a co-transport process. Nb(V) can be concentrated in the stripping solution and the SLM showed a good performance for Nb–Ta separation.

Nitrate uptake and extracellular alkalinization by the green alga Hydrodictyon reticulatum in blue and red light

Abstract Key words: Alkalinization, blue light, Hydrodictyon, nitrateuptake, stoichiometry nitrate/protons.Nitrate uptake and the medium alkalinization relatedto it were studied with nets of the coenocytic, giantcell, green alga Hydrodictyon reticulatum. A compar- Introduction ison of red, blue and white light irradiation showed nospecial control of nitrate uptake and of the corres- In several species of microalgae, blue light signals areponding alkalinization of the external medium by light involved in nitrate uptake and nitrate reduction, but soquality, but rather a response as expected for the far it has been unknown whether this is a general charac-photosynthetic apparatus. In the dark, nitrate uptake teristic of all algae or specifically of microalgae. Bothrates amounted to one-fifth of those in saturating nitrate uptake and nitrate reduction depend on metabolicwhite light. This is in contrast to the chlorococcal energy (Ullrich, 1983, 1992). Nitrate uptake depends onmicroalga Monoraphidium braunii, where blue light ATP via the plasma membrane H+-ATPase in a secondaryspecifically switched on nitrate uptake-dependent active H+co-transport process. Nitrate reduction requiresalkalinization and where uptake and reduction of reducing equivalents. The subsequent ammonium assim-nitrate strongly depended on blue light; the rates in ilation via GS-GOGAT requires ATP, reducing equiva-pure red light and in the dark being very low. The lents and the supply of carbon skeletons. Enzymes ofstoichiometric ratio between nitrate taken up and nitrate assimilation, including the membrane carriers,extracellular alkalinization was close to 1 (0.86) in air have constitutive components to maintain a low level ofwith CO activity in the dark or in the absence of substrate. Nitrate,2but close to 2 (1.84) in N2for nitrate pre-loaded cells. In the absence of any carbon source, a as well as nitrite, usually induces high amounts andhigh proportion of the absorbed and reduced nitrogen activities of the related proteins, but in many casesis released, most of it as ammonium which causes the induction additionally requires light. In the microalga M.excess alkalinization and some as nitrite, which lowers braunii, short-term N starvation for a few hours in thethe ratio. Nitrite and ammonium release rates under light promotes the greatest increase in nitrate assimilationanaerobic, CO (Ullrich et al., 1981). However, algal families or even2-free conditions were also independentof red or blue light and continued for several hours individual species may behave diVerently in their responsewhen the medium was buffered at pH 6. The data indi- to light, particularly to light quality, whereas nitrate andcate that nitrate uptake, but less its reduction, is regu- nitrite always support the induction of their own meta-lated differently in vacuolate, coenocytic algae from bolic machinery, particularly in the absence of externalNH+4microalgae. In Hydrodictyon, nitrate uptake and reduc- . In these respects, pioneer studies were carried outtion seem to be controlled by energy supply; in various with the unicellular microalgae Chlorella (Calero et al.,microalgae, in addition, it is controlled specifically by 1980), Monoraphidium (Quin˜ones and Aparicio, 1990;blue light. Aparicio et al., 1994) and Chlamydomonas (Azuara and

Modulation of Chloride Secretion Across the Pigmented Rabbit Conjunctiva

The purpose of the present study was to investigate whether active Cl−secretion in the pigmented rabbit conjunctiva was subject to cAMP, Ca2+and protein kinase C (PKC) modulation. The excised pigmented rabbit conjunctivas were mounted in the modified Ussing-type chambers for measurement of unidirectional36Cl fluxes under the open-circuit condition and of the short-circuit current (Isc), potential difference, and transconjunctival electrical resistance. The results indicate that Cl−secretion across the conjunctiva was abolished by mucosal application of 1 mMN-phenylanthranilic acid and was reduced by 40% by serosal application of 10 μMbumetanide. Net Cl−flux was stimulated by 133% by 1 mM8-Br cAMP, 107% by 10 μMA23187, and 87% by 1 μMphorbol 12-myristate-13-acetate (PMA), suggesting that cAMP, Ca2+, and PKC all modulated active Cl−secretion, respectively. There existed a linear correlation between measured changes in net Cl−flux and observed changes in Isc(r2=0.99). The serial treatment of the conjunctiva with (a) 1 mM8-Br cAMP and 10 μMA23187 and (b) 10 μMA23187 and 1 μMPMA resulted in sequence-independent, additive stimulation of Isc. In the case of 1 mM8-Br cAMP and 1 μMPMA, additive stimulation of Iscwas observed only when 1 mM8-Br cAMP was added prior to 1 μMPMA. These results suggest that a given pharmacological agent may affect more than one channel type and that there might be a possible connection among the channels at the signal transduction level. In summary, Cl−appears to enter the pigmented rabbit conjunctiva from the serosal fluid via Na+-(K+)-2Cl−cotransport process and exit to the mucosal fluid via channels, resulting in active Cl−secretion. Active Cl−secretion in the pigmented rabbit conjunctiva appears to be modulated by cAMP, Ca2+, and PKC.