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R A Vaughan

Publications and source records attributed to R A Vaughan.

At least 19 recordsLinked to original sources
PubMed1998

Multiple binding sites for [125I]RTI-121 and other cocaine analogs in rat frontal cerebral cortex.

In an effort to identify novel binding sites for cocaine and its analogs, we carried out binding studies with the high-affinity and selective ligand [125I]RTI-121 in rat frontal cortical tissue. Very low densities of binding sites were found. Saturation analysis revealed that the binding was to both high- and low-affinity sites. Pharmacological competition studies were carried out with inhibitors of the dopamine, norepinephrine, and serotonin transporters. The various transporter inhibitors inhibited the binding of 15 pM [125I]RTI-121 in a biphasic fashion following a two-site binding model. The resultant data were complex and did not suggest a simple association with any single transporter. Correlational analysis supported the following hypothesis: [125I] RTI-121 binds to known transporters and not to novel sites; these include dopamine, norepinephrine, and serotonin transporters. Immunoprecipitation of transporters photoaffinity labeled with [125]RTI-82 and subsequent analysis of SDS-page gels revealed the presence of authentic dopamine transporters in these samples; displacement of the photoaffinity label occurred with a typical dopamine transporter pharmacology. These data are compatible with the binding properties of RTI-121 and the presence of several known transporters in the tissue studied.

Animals↗
PubMed1997

The dopamine transporter: comparative ultrastructure of dopaminergic axons in limbic and motor compartments of the nucleus accumbens.

The dopamine transporter (DAT) regulates extracellular dopamine concentrations, transports neurotoxins, and acts as a substrate for cocaine reinforcement. These functions are known to differ in the limbic-associated shell and motor-associated core compartments of the nucleus accumbens (NAc). Previous studies have shown differential expression of DAT in the NAc shell and core but were limited in resolution to the regional level. Thus, it is not known whether there are differences in the amount, subcellular localization, or plasmalemmal targeting of DAT within individual dopaminergic axons in the two regions. We used high-resolution electron microscopic immunocytochemistry to investigate these possibilities. We show that in both the shell and core, DAT immunogold labeling is present in tyrosine hydroxylase-immunoreactive varicose axons that form symmetric synapses. Within these labeled axons, most DAT gold particles are located on extrasynaptic plasma membranes, but some are associated with intracellular membranes. Dopaminergic axons in the shell contain lower mean densities of both total DAT gold particles (per square micron) and plasmalemmal DAT gold particles (per micron) than those in the core. Within labeled axons in the NAc shell and core, however, there are no detectable differences in the subcellullar distribution of DAT or the percentage of total DAT gold particles that are located on plasma membranes. These studies are the first to examine and compare the subcellular localization of DAT in the NAc shell and core. As a result, they identify intrinsic, cell-specific differences in the expression of DAT within dopaminergic axons in these functionally distinct striatal compartments.

Animals↗
PubMed1997

Immunogold localization of the dopamine transporter: an ultrastructural study of the rat ventral tegmental area.

The dopamine transporter (DAT) plays an important role in the plasmalemmal reuptake of dopamine and, thus, in the termination of normal dopaminergic neurotransmission. DAT is also a major binding site for cocaine and other stimulants, the psychoactive effects of which are associated primarily with the inhibition of dopamine reuptake within mesocorticolimbic dopaminergic neurons. We used electron microscopy with an anti-peptide antiserum directed against the N-terminal domain of DAT to determine the subcellular localization of this transporter in the rat ventral tegmental area (VTA), the region that contains the cell bodies and dendrites of these dopaminergic neurons. We show that in the VTA, almost 95% of the DAT immunogold-labeled profiles are neuronal perikarya and dendrites, and the remainder are unmyelinated axons. Within perikarya and large proximal dendrites, almost all of the DAT immunogold particles are associated with intracellular membranes, including saccules of Golgi and cytoplasmic tubulovesicles. In contrast, within medium- to small-diameter dendrites and unmyelinated axons, most of the DAT gold particles are located on plasma membranes. In dually labeled tissue, peroxidase reaction product for the catecholamine-synthesizing enzyme tyrosine hydroxylase is present in DAT-immunoreactive profiles. These findings suggest that intermediate and distal dendrites are both the primary sites of dopamine reuptake and the principal targets of cocaine and related psychostimulants within dopaminergic neurons in the VTA.

Animals↗
PubMed1997

Protein kinase C-mediated phosphorylation and functional regulation of dopamine transporters in striatal synaptosomes.

Dopamine transporters (DATs) are members of a family of Na+- and Cl--dependent neurotransmitter transporters responsible for the rapid clearance of dopamine from synaptic clefts. The predicted primary sequence of DAT contains numerous consensus phosphorylation sites. In this report we demonstrate that DATs undergo endogenous phosphorylation in striatal synaptosomes that is regulated by activators of protein kinase C. Rat striatal synaptosomes were metabolically labeled with [32P]orthophosphate, and solubilized homogenates were subjected to immunoprecipitation with an antiserum specific for DAT. Basal phosphorylation occurred in the absence of exogenous treatments, and the phosphorylation level was rapidly increased when synaptosomes were treated with the phosphatase inhibitors okadaic acid or calyculin. Treatment of synaptosomes with the protein kinase C activator phorbol 12-myristate 13-acetate (PMA) also increased the level of phosphate incorporation. This occurred within 10 min and was dosedependent between 0.1 and 1 microM PMA. DAT phosphorylation was also significantly increased by two other protein kinase C activators, (-)-indolactam V and 1-oleoyl-2-acetyl-sn-glycerol. The inactive phorbol ester 4alpha-phorbol 12,13-didecanoate at 10 microM was without effect, and PMA-induced phosphorylation was blocked by treatment of synaptosomes with the protein kinase C inhibitors staurosporine and bisindoylmaleimide. These results indicate that DATs undergo rapid in vivo phosphorylation in response to protein kinase C activation and that a robust mechanism exists in synaptosomes for DAT dephosphorylation. Dopamine transport activity in synaptosomes was reduced by all treatments that promoted DAT phosphorylation, with comparable dose, time, and inhibitor characteristics. The change in transport activity was produced by a reduction in Vmax with no significant effect on the Km for dopamine. These results suggest that synaptosomal dopamine transport activity is regulated by phosphorylation of DAT and present a potential mechanism for local neuronal control of synaptic neurotransmitter levels and consequent downstream neural activity.

Animals↗
PubMed1997

Immunogold localization of the dopamine transporter: an ultrastructural study of the rat ventral tegmental area.

The dopamine transporter (DAT) plays an important role in the plasmalemmal reuptake of dopamine and, thus, in the termination of normal dopaminergic neurotransmission. DAT is also a major binding site for cocaine and other stimulants, the psychoactive effects of which are associated primarily with the inhibition of dopamine reuptake within mesocorticolimbic dopaminergic neurons. We used electron microscopy with an anti-peptide antiserum directed against the N-terminal domain of DAT to determine the subcellular localization of this transporter in the rat ventral tegmental area (VTA), the region that contains the cell bodies and dendrites of these dopaminergic neurons. We show that in the VTA, almost 95% of the DAT immunogold-labeled profiles are neuronal perikarya and dendrites, and the remainder are unmyelinated axons. Within perikarya and large proximal dendrites, almost all of the DAT immunogold particles are associated with intracellular membranes, including saccules of Golgi and cytoplasmic tubulovesicles. In contrast, within medium- to small-diameter dendrites and unmyelinated axons, most of the DAT gold particles are located on plasma membranes. In dually labeled tissue, peroxidase reaction product for the catecholamine-synthesizing enzyme tyrosine hydroxylase is present in DAT-immunoreactive profiles. These findings suggest that intermediate and distal dendrites are both the primary sites of dopamine reuptake and the principal targets of cocaine and related psychostimulants within dopaminergic neurons in the VTA.

Animals↗
PubMed1997

Phorbol esters increase dopamine transporter phosphorylation and decrease transport Vmax.

Sodium- and chloride-coupled transport of dopamine from synapses into presynaptic terminals plays a key role in terminating dopaminergic neurotransmission. Regulation of the function of the dopamine transporter, the molecule responsible for this translocation, is thus of interest. The primary sequence of the dopamine transporter contains multiple potential phosphorylation sites, suggesting that the function of the transporter could be regulated by phosphorylation. Previous work from this laboratory has documented that phorbol ester activation of protein kinase C (PKC) decreases dopamine transport Vmax in transiently expressing COS cells. In the present report, we document in vivo phosphorylation of the rat dopamine transporter stably expressed in LLC-PK1, cells and show that phosphorylation is increased threefold by phorbol esters. Dopamine uptake is also regulated by phorbol esters in these cells; phorbol 12-myristate 13-acetate (PMA) reduces transport Vmax by 35%. Parallels between the time course, concentration dependency, and staurosporine sensitivity of alterations in transporter phosphorylation and transporter Vmax suggest that dopamine transporter phosphorylation involving PKC could contribute to this decreased transporter function. Phosphorylation of the dopamine transporter by PKC or by a PKC-activated kinase could be involved in rapid neuroadaptive processes in dopaminergic neurons.

Alanine↗
PubMed1996

Dopamine transporter ligand binding domains. Structural and functional properties revealed by limited proteolysis.

Dopamine transporters (DATs) are members of the Na+- and Cl--dependent neurotransmitter and amino acid transporter family predicted by hydrophobicity analysis to have 12 transmembrane-spanning helices. The structure of DAT was studied using the photoaffinity compounds [125I]1-[2-(diphenylmethoxy)-ethyl]-4-[2-(4-azido-3-iodophenyl) ethyl] piperazine ([125I]DEEP), a 1-(2-diphenylmethoxy)-ethyl-4-(3-phenyl propyl)piperazine (GBR analog), and [125I]-3beta-(p-chlorophenyl)tropane-2beta-carboxylic acid, 4'-azido-3'-iodophenylethyl ester ([125I]RTI 82), a cocaine analog, which had been shown in a previous study to become incorporated into different regions of the DAT primary sequence. The proximity of the photolabeled binding sites to integral membrane structures was investigated by subjecting photolabeled membrane suspensions to limited proteolysis with trypsin and separately analyzing the resulting membranes and supernatants for the presence of photolabeled DAT fragments. Trypsin treatment of [125I] DEEP-labeled membranes generated labeled 45- and 14-kDa DAT fragments that immunoprecipitated with an epitope-specific antiserum generated against amino acids 42-59 near the first putative transmembrane domain, whereas [125I]RTI 82 was found in 32- and 16-kDa tryptic fragments that precipitated with an antiserum directed against a sequence near transmembrane domain 4 (amino acids 225-238). All of the photolabeled fragments were recovered in the protease-treated membranes, indicating that they possess integral membrane structures that prevent their release from the membrane as soluble forms. The size of the two smallest fragments in conjunction with their retention in the membrane suggests that incorporation of the photoaffinity ligands occurs in or near membrane spanning regions and delineates the maximum possible distance between the transmembrane structures, incorporated photolabel, and antibody epitopes. Carbohydrate analysis of the fragments identified sialic acids and N-linked oligosaccharides exclusively on the 45-kDa [125I]DEEP-labeled fragment, which, based on size, would be expected to contain four consensus glycosylation sites between putative transmembrane domains 3 and 4. Photoaffinity labeling after trypsin treatment of membranes showed that the larger but not the smaller fragments retain binding capacity, as the 45- and 32-kDa fragments were capable of becoming photolabeled. Binding of photoaffinity ligands at these fragments was displaced with the same pharmacology as that of intact DATs. These results verify numerous aspects of DAT structure and topology heretofore only predicted from theoretical considerations and extend our knowledge of DAT structure-function properties.

Affinity Labels↗
PubMed1996

The dopamine transporter is localized to dendritic and axonal plasma membranes of nigrostriatal dopaminergic neurons.

Nigrostriatal dopaminergic neurons play an essential role in the central regulation of motor functions. These functions are initiated through the release of dopamine from axon terminals in the striatum or from dendrites in the substantia nigra (SN) and are terminated by the reuptake of dopamine by the sodium- and chloride-dependent dopamine transporter (DAT). DAT also can transport dopamine neurotoxins and has been implicated in the selective vulnerability of nigrostriatal dopaminergic neurons in major models of Parkinson's disease. We have used electron microscopic immunocytochemistry with an N-terminal domain anti-peptide antibody to examine the subcellular distribution of DAT in the rat SN and dorsolateral striatum. In the SN, immunogold labeling for DAT was localized to cytoplasmic surfaces of plasma membranes and smooth endoplasmic reticulum of dendrites and dendritic spines, few of which contained synaptic vesicles. Neuronal perikarya in the SN contained immunogold-labeled pleomorphic electron-lucent tubulovesicles but showed immunolabeling of plasma membranes only rarely. Axon terminals in the striatum contained extensive immunogold labeling of cytoplasmic surfaces of plasma membranes near aggregates of synaptic vesicles and less frequent labeling of intervaricose segments of plasma membrane or small electron-lucent vesicles. In sections dually labeled for DAT and the catecholamine-synthesizing enzyme tyrosine hydroxylase, both markers were colocalized in most profiles in the SN and striatum. These findings support the proposed topological model for DAT and suggest that this transporter is strategically located to facilitate uptake of dopamine and neurotoxins into distal dendritic and axonal processes of nigrostriatal dopaminergic neurons.

Amino Acid Sequence↗
PubMed1996

Species- and brain region-specific dopamine transporters: immunological and glycosylation characteristics.

Dopamine transporters (DATs) from the caudate nucleus of four species (rat, mouse, dog, and human) and four regions of rat brain (striatum, nucleus accumbens, prefrontal cortex, and midbrain) were photoaffinity labeled and analyzed by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis for cross-reactivity to four epitope-specific rat antipeptide antibodies. Each of these antibodies varied in its efficiency at recognizing DAT. The DATs from the rat brain regions exhibited the same degree of recognition by each of the four sera, a result compatible with these proteins being the product of a single gene. The DATs from the different species were recognized by all four sera but with different efficiencies, possibly relating to amino acid sequence differences within the immunizing epitope. All of the photolabeled, immunoprecipitated DATs migrated with a molecular mass of approximately 80 kDa, and no lower molecular mass forms were found. The DATs from all species and brain regions tested were shown by enzymatic deglycosylation to contain N-linked carbohydrates and sialic acids in amounts comparable with rat striatal DATs. The finding that no photolabeled DAT forms < 80 kDa were isolated from membranes indicates that partially or incompletely glycosylated forms are not present, even in the midbrain cell bodies where immature forms might be expected to be found. These findings verify the utility of these anti-rat antibodies as biochemical tools for studying DATs from other species and extend our knowledge of biochemical characteristics of DATs from these species and brain regions.

Affinity Labels↗
PubMed1995

Dopamine transporter immunoreactivity in rat brain.

The dopamine transporter (DAT) is a primary site for the action of cocaine in inducing euphoria. Its action is necessary for the selectivities of dopaminergic neurotoxins that provide the best current experimental models of Parkinson's disease. In the present report, rat dopamine transporter-like immunoreactivity (iDAT) was assessed by immunohistochemistry using newly developed polyclonal antisera raised against conjugated peptides corresponding to sequences found in the dopamine transporter's carboxy- and amino-termini. Dense iDAT was observed in patterns consistent with neural processes and terminals in the striatum, nucleus accumbens, olfactory tubercle, nigrostriatal bundle, and lateral habenula. Perikarya in the substantia nigra pars compacta were immunostained with moderate intensity using one of two immunohistochemical methods, while scattered ventral tegmental area perikarya were stained with somewhat less intensity. Immunoreactive neuronal processes with axonal and dendritic morphologies were stained in the substantia nigra and the paranigral and parabrachialis pigmentosus nuclei of the ventral tegmental area, while sparser processes were noted more medially in the ventral tegmental area. Neuronal processes were found in several laminae in the cingulate cortex, with notable fiber densities in the superficial aspects of lamina I and laminae II/III. The intensities of immunoreactivities in striatum and cerebral cortex were dramatically attenuated ipsilateral to nigrostriatal bundle 6-hydroxydopamine lesions. Specificity of immunostaining was supported by agreement of the results using sera directed against two distinct DAT segments, studies with preimmune and preadsorbed sera and studies of the extracted protein. These antisera identify and reveal details of the distribution of DAT immunoreactivity in rat brain and display variations in levels of DAT expression of likely functional significance.

Amino Acid Sequence↗
PubMed1995

Photoaffinity-labeled ligand binding domains on dopamine transporters identified by peptide mapping.

Binding domains on rat dopamine transporters for cocaine and 1-(2-diphenylmethoxy)ethyl-4-(3-phenylpropyl)piperazine compounds were identified using controlled proteolysis of photoaffinity-labeled protein and epitope-specific immunoprecipitation of the labeled fragments. Rat dopamine transporters were photoaffinity labeled with 1-[2-(diphenylmethoxy)ethyl]-4-[2-(4-azido- 3-[125I]iodophenyl)ethyl]piperazine ([125I]DEEP) [a 1-(2-di- phenylmethoxy)ethyl-4-(3-phenylpropyl)piperazine analog] or 3 beta-(p-chlorophenyl)tropane-2 beta-carboxylic acid, 4'-azido-3'- [125I]iodophenylethyl ester ([125I]RTI 82) (a cocaine analog) and were gel purified to remove contaminating radioactivity. The resulting samples were treated with V8 protease or trypsin and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The peptide maps generated with each enzyme were different for each of the ligands, suggesting that the ligands were incorporated into different regions of the protein. Identical peptide maps were generated from striatum- and nucleus accumbens-derived transporters, indicating that these polypeptides are highly similar in primary sequence. The proteolytic fragments generated by V8 protease were localized to specific domains of the protein using antipeptide antibodies corresponding to five different regions of the transporter. Fragments of 10 and 7 kDa from [125I]DEEP-labeled transporters were specifically immunoprecipitated with an antibody generated against amino acids 42-59 (near the first putative trans-membrane domain), whereas a 34-kDa fragment from [125I]RTI 82-labeled transporters was precipitated with three different sera corresponding to regions in the carboxyl-terminal two thirds of the protein. None of the V8 fragments smaller than 45 kDa, containing either photolabel, was altered in molecular mass by N-deglycosylation. The results indicate that photoincorporation of [125I]DEEP occurs in the amino half of the dopamine transporter, near the first two transmembrane helices, whereas [125I]RTI 82 labels the carboxyl-terminal region of the protein, between transmembrane domains 4 and 12.

Affinity Labels↗
PubMed1994

Developmentally regulated glycosylation of dopamine transporter.

The dopamine transporter (DAT) in rat striatum was examined during postnatal development and aging after photolabeling with [125I]DEEP. The DAT-[125I]DEEP protein complex from adult rats (2 months) appeared as a broad diffuse band in SDS-PAGE gels with average apparent molecular mass of about 80,000 Da as previously found. However, the molecular mass was lower at birth (day 0) and at postnatal ages 4 and 14 days. In aged rats (104 weeks), the molecular mass was slightly higher than that found in young adults (60 days). In binding experiments with [3H]BTCP, there were age-related differences in Kd and Bmax with decreases in both Kd and Bmax found in aged rats. Treatment of photolabeled membranes with neuraminidase caused a reduction in DAT molecular mass, but age-related differences were maintained. Treatment with N-glycanase greatly reduced or eliminated the age-related differences. Several DAT peptide-specific polyclonal antibodies immunoprecipitated DAT-[125I]DEEP protein complex at different developmental ages. Taken together, these results suggest differential glycosylation of rat DAT occurs during postnatal development and aging; the increase is due to increases in the N-linked sugars rather than changes in either sialic acid content or the polypeptide.

Aging↗
PubMed1992

Microheterogeneity of dopamine transporters in rat striatum and nucleus accumbens.

Previously we have shown that the [125I]DEEP-labeled dopamine transporter from the rat nucleus accumbens has a higher apparent molecular weight than that from striatum. The present study confirms and extends these observations. Experiments with nucleus accumbens showed [125I]-DEEP to specifically bind to a protein with an apparent molecular weight of 76 kDa and with the pharmacological properties of the dopamine transporter. In exoglycosidase studies, treatment with neuraminidase, but not alpha-mannosidase, reduced the apparent molecular weight of the dopamine transporter from both the striatum and nucleus accumbens; however, a difference in the apparent molecular weight was still observed. N-Glycanase treatment, on the other hand, did reduce the apparent molecular weight of the dopamine transporters from the two regions to a similar value, approximately 56 kDa. In radioligand binding studies examining the effect of partial deglycosylation on striatal dopamine transporters, neuraminidase did not affect specific [3H]WIN 35,428 binding at 4 and 40 nM concentrations. In conclusion, the present study demonstrates that the difference in the apparent molecular weight of the dopamine transporter from these two regions is due to a difference in glycosylation and that the dopamine transporter from both regions contains similar amounts of sialic acid in their carbohydrate structure. Furthermore, the present data also indicate that the polypeptide portion of the dopamine transporter from both regions could be the same gene product.

Animals↗
PubMed1992

Pancreatic pseudocyst: diagnosis and management.

Diagnosis and management of pseudocysts of the pancreas often present difficult clinical problems. We reviewed our 18 patients with pancreatic pseudocysts treated between January 1985 and October 1989 to identify criteria for operative and nonoperative management based on size of the lesion on computerized tomography. Diagnostic modalities, etiology, management, and concurrent medical problems were also evaluated. Alcohol (72%) was the most common etiologic agent. Hypertension (39%), peptic ulcer disease (28%), and chronic obstructive pulmonary disease (22%) were the most common associated medical problems. CT scan was the most frequently used (100%) and most accurate (100%) preoperative diagnostic tool. Preoperative ERCP modified the treatment plan in only one patient. All pseudocysts smaller than 3 cm on CT scan were managed nonoperatively, without recurrence (mean follow-up of 3 months). The most commonly performed surgical procedure was cystogastrostomy. External drainage procedures had a higher complication rate (100% vs 14%) and higher recurrence rate (33% vs 0%) than internal drainage procedures. Attempted percutaneous drainage in one patient resulted in recurrence. Pancreatic pseudocysts less than 3 cm in diameter can be safely managed nonoperatively. CT scan remains the diagnostic tool of choice. Preoperative ERCP evaluation is of limited utility and needs further evaluation. Internal drainage procedures provide the best surgical results.

Adult↗
PubMed1991

Overexpression of the cAMP receptor 1 in growing Dictyostelium cells.

cAR1, the cAMP receptor expressed normally during the early aggregation stage of the Dictyostelium developmental program, has been expressed during the growth stage, when only low amounts of endogenous receptors are present. Transformants expressing cAR1 have 7-40 times over growth stage and 3-5-fold over aggregation stage levels of endogenous receptors. The high amounts of cAR1 protein expressed constitutively throughout early development did not drastically disrupt the developmental program; the onset of aggregation was delayed by 1-3 h, and then subsequent stages proceeded normally. The affinity of the expressed cAR1 was similar to that of the endogenous receptors in aggregation stage cells when measured either in phosphate buffer (two affinity states with Kd's of approximately 30 and 300 nM) or in 3 M ammonium sulfate (one affinity state with a Kd of 2-3 nM). When expressed during growth, cAR1 did not appear to couple to its normal effectors since these cells failed to carry out chemotaxis or to elevate cGMP or cAMP levels when stimulated with cAMP. However, cAMP stimulated phosphorylation, and loss of ligand binding of cAR1 did occur. Like aggregation stage control cells, the cAR1 protein shifted in apparent molecular mass from 40 to 43 kDa and became highly phosphorylated when exposed to cAMP. In addition, the number of surface cAMP binding sites in cAR1 cells was reduced by over 80% during prolonged cAMP stimulation. These results define a useful system to express altered cAR1 proteins and examine their regulatory functions.

Cyclic AMP↗
PubMed1991

A rapid binding assay for solubilized dopamine transporters using [3H]WIN 35,428.

The cocaine analog [3H]WIN 35,428 was used to label digitonin-solubilized dopamine transporters from dog caudate nucleus. The assay consists of incubation of extracts with the ligand followed by separation of free from bound ligand by centrifugation after adding activated charcoal. Specific binding was observed in dog caudate but was absent in dog cerebellar extracts. Binding was linear with tissue, saturable, and of high affinity (Kd = 16 nM). In competition studies, soluble [3H]WIN 35,428 binding was inhibited strongly by mazindol, GBR 12909, and (-)-cocaine but only weakly by citalopram, desipramine, and (+)-cocaine; this is typical of binding to the dopamine transporter. Compared to assays using [3H]GBR 12935, (-)-cocaine was relatively more potent, suggesting that the cocaine and GBR 12935 binding sites are somewhat different. When soluble extract was chromatographed on a wheat germ agglutinin-Sepharose column, [3H]WIN 35,428 binding activity was eluted with N-acetylglucosamine in a manner similar to photoaffinity-labeled dopamine transporters.

Adsorption↗