Active transport of 5-hydroxyindoleacetic acid by the rabbit choroid plexus in vitro: Blockade by probenecid and metabolic inhibitors
Abstract
When rabbit choroid plexuses were incubated at 37° with Krebs-Ringer solutions of [14C]5-hydroxyindoleacetic acid (5-HIAA), the tissue took up the acid by a process showing all the characteristics of active transport. Uptake against a concentration gradient occurred by a saturable process that was inhibited by several metabolic inhibitors. The transport of 5-HIAA was also inhibited by probenecid and para-aminohippuric acid, known inhibitors of organic acid transport systems in many organs. 5-HIAA was found to bind to homogenates of choroid plexus, but the binding would not account for the bulk of acid accumulation seen in the intact tissue. Moreover, the transport of 5-HIAA in rabbit brain cortex slices was not affected by probenecid.
References (13)
- H.C. Guldberg et al.
Life Sci.
(1966) - W.D. Reid et al.
Life Sci.
(1968) - Y. Tochino et al.
Biochem. Pharmac.
(1965) - J.V. Taggart
Am. J. Med.
(1958) - N.H. Neff et al.
J. Pharmac. exp. Ther.
(1967) - J. Forn et al.
Cited by (34)
Renal Organic Cation and Anion Transport: From Physiology to Genes
2010, Comprehensive Toxicology, Second EditionThe plasma membrane of a mammalian cell represents a significant impediment to the cellular entry and exit of charged organic compounds. To aid transcellular flux of such molecules, transporter proteins exist in the plasma membrane of barrier epithelia and endothelia. One such family of transporters, the organic cation/anion/zwitterion transporter family (Slc22), mediates the permeation of small, hydrophilic, positively and negatively charged organic compounds. Some examples of compounds that fall into this category of molecules include drugs, environmental pollutants and toxins, hormones, neurotransmitters, and their metabolites. Concentration and duration of exposure are important contributing factors to adverse effects and toxicities associated with these compounds. Therefore, efficient and rapid removal upon exposure is a critical detoxification function of the excretory organs of the body, which includes the kidneys. Glomerular filtration and tubular organic ion transport, which are dependent on continuous renal blood flow, are the main determinants of renal excretion. Thus, active transport often leads to marked substrate accumulation in renal proximal tubule cells and is a major causative factor of the nephrotoxicity that frequently accompanies systemic exposure and/or pathophysiological states. This chapter will review the physiological and biochemical advances that led to the identification and cloning of renal organic cation and anion transporters; provide an overview of their tissue expression profiles, membrane localization, and mechanisms of action; and provide evidence from the literature linking their function and/or dysfunction to the toxicity of various xenobiotic and endogenous agents.
Tryptophan metabolism via serotonin in human CSF of different brain sites using a new neuroendoscopic technique
2007, International Congress SeriesA new neuroendoscopic technique has permitted a precise and accurate exploration of all the cerebral ventricles, making possible the study of the CSF of the lateral ventricles and, above all, the CSF adjacent to the walls of the third ventricle in humans. The concentrations of tryptophan and its metabolites via serotonin were measured in the CSF of different sites of the cerebral cavity, in particular in the third ventricle. Patients affected with non-communicating hydrocephalus undergoing neuroendoscopic third ventriculostomy were enrolled in the study. As controls, subjects not suffering from any neurological disease, who underwent lumbar subarachnoid anaesthesia for minor surgical procedures, provided lumbar CSF, and patients affected by Chiari malformation provided cisternal and right ventricular CSF. Tryptophan concentration was higher in right ventricular CSF than in lumbar CSF. Serotonin (5-HT) was detectable in the CSF of the right ventricle of hydrocephalic individuals. 5-Hydroxyindoleacetic acid (5-HIAA) was higher in the right ventricular CSF than in the cisternal and lumbar CSF both in controls and hydrocephalic subjects. However, the 5-HIAA level was higher in the right ventricular and cisternal CSF in hydrocephalic individuals in comparison to controls. 5-HT presented the highest concentration in the pineal recess, whereas the highest amounts of 5-HIAA were found in the choroids plexus, third and right ventricles and the lowest in the pineal recess, subarachnoid space and intepeduncular cistern. Melatonin is more concentrated within the ventricles, in particular the third ventricle, and in the CSF pineal recess.
The use of this neuroendoscopic technique in hydrocephalic patients provides new insight into the metabolic pathway of tryptophan via serotonin in the CSF.
Organic anion transporter (Slc22a) family members as mediators of toxicity
2005, Toxicology and Applied PharmacologyExposure of the body to toxic organic anions is unavoidable and occurs from both intentional and unintentional sources. Many hormones, neurotransmitters, and waste products of cellular metabolism, or their metabolites, are organic anions. The same is true for a wide variety of medications, herbicides, pesticides, plant and animal toxins, and industrial chemicals and solvents. Rapid and efficient elimination of these substances is often the body's best defense for limiting both systemic exposure and the duration of their pharmacological or toxicological effects. For organic anions, active transepithelial transport across the renal proximal tubule followed by elimination via the urine is a major pathway in this detoxification process. Accordingly, a large number of organic anion transport proteins belonging to several different gene families have been identified and found to be expressed in the proximal nephron. The function of these transporters, in combination with the high volume of renal blood flow, predisposes the kidney to increased toxic susceptibility. Understanding how the kidney mediates the transport of organic anions is integral to achieving desired therapeutic outcomes in response to drug interactions and chemical exposures, to understanding the progression of some disease states, and to predicting the influence of genetic variation upon these processes. This review will focus on the organic anion transporter (OAT) family and discuss the known members, their mechanisms of action, subcellular localization, and current evidence implicating their function as a determinant of the toxicity of certain endogenous and xenobiotic agents.
Mechanism of organic anion transport across the apical membrane of choroid plexus
1999, Journal of Biological ChemistryThe mechanism and membrane localization of choroid plexus (CP) organic anion transport were determined in apical (or brush border) membrane vesicles isolated from bovine choroid plexus and in intact CP tissue from cow and rat. Brush border membrane vesicles were enriched in Na+,K+-ATPase (20-fold; an apical marker in CP) and demonstrated specific, sodium-coupled transport of proline, glucose, and glutarate. Vesicular uptake of the anionic herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) was markedly stimulated by an inward sodium gradient but only in the presence of glutarate, indicating the presence of apical dicarboxylate/organic anion exchange. Consistent with this interpretation, an imposed outward glutarate gradient stimulated 2,4-D uptake in the absence of sodium. Under both conditions, uptake was dramatically slowed and overshoot was abolished by probenecid. Likewise, apical accumulation of 2,4-D by intact bovine choroid plexus tissue in vitro was stimulated by external glutarate in the presence of sodium. Glutarate stimulation was abolished by 5 mm LiCl. Identical findings were obtained using rat CP tissue, which showed both sodium/glutarate-stimulated 2,4-D (tissue/medium (T/M) ∼ 8) andp-aminohippurate (T/M = 2) transport. Finally, since the renal exchanger (rROAT1) has been cloned in rat kidney, a rROAT1-green fluorescent protein construct was used to analyze exchanger distribution directly in transiently transfected rat CP. As predicted by the functional studies, the fluorescently tagged transporter was seen in apical but not basolateral membranes of the CP.
Role of efflux transport across the blood-brain barrier and blood- cerebrospinal fluid barrier on the disposition of xenobiotics in the central nervous system
1997, Advanced Drug Delivery ReviewsThe disposition of hydrophilic organic anions and cations in the central nervous system (CNS) was studied in relation to the transport properties across the blood-brain barrier (BBB) and the blood-cerebrospinal fluid (CSF) barrier, using β-lactam antibiotics and cimetidine as model compounds. The concentration profiles for cefodizime in the rat CNS were analyzed using a spatially distributed model. The model analysis revealed that the drug penetration into the CSF after i.v. administration can be accounted for by permeation across the BBB and diffusion through the brain extracellular fluid (ECF) and across the ependymal surface into the CSF. In in situ and in vivo experiments, we found that the β-lactam antibiotics are transported across the BBB via a carrier-mediated mechanism. In addition, by analyzing the ligand amount remaining in the brain after microinjection into the cerebral cortex (brain efflux index method), it was clarified that some organic anions are also eliminated from the brain ECF into the blood across the BBB via a specific mechanism. The organic anions are also eliminated from the CSF by the bulk flow and by the active transport system in the choroid plexus which forms the blood-CSF barrier. Comparison of kinetic parameters determined in in vivo and in vitro experiments revealed that (1) the choroid plexus is the predominant site for the elimination of β-lactam antibiotics from the CSF and (2) the isolated choroid plexus can be a useful tool to predict the in vivo elimination clearance. We also found that an anionic exchanger, at least in part, plays a role in the uphill transport of β-lactam antibiotics in the choroid plexus. New quinolones (such as fleroxacin) are also transported by the mechanism shared by β-lactam antibiotics. Transport properties of cimetidine, a prototypic organic cation, in the choroid plexus was also characterized in in vivo, in situ and in vitro experiments. Although cimetidine was transported by a specific mechanism, no inhibitory effect of tetraethylammonium, N1-methylnicotinamide, or choline was observed. In contrast, a mutual inhibition between cimetidine and benzylpenicillin transport was observed. Other examples for such interactions are also summarized, although the molecular mechanism for the transport still remains to be clarified.
Neuroendocrine regulatory mechanisms in the choroid plexus-cerebrospinal fluid system
1992, Brain Research ReviewsThe CSF is often regarded as merely a mechanical support for the brain, as well as an unspecific sink for waste products from the CNS. New methodology in receptor autoradiography, immunohistochemistry and molecular biology has revealed the presence of many different neuroendocrine substances or their corresponding receptors in the main CSF-forming structure, the choroid plexus. Both older research on the sympathetic nerves and recent studies of peptide neurotransmitters in the choroid plexus support a neurogenic regulation of choroid plexus CSF production and other transport functions. Among the endocrine substances present in blood and CSF, 5-HT, ANP, vasopressin and the IGFs have high receptor concentrations in the choroid plexus and have been shown to influence choroid plexus function. Finally, the choroid plexus produces the growth factor IGF-II and a number of transport proteins, most importantly transthyretin, that might regulate hormone transport from blood to brain. These studies suggest that the choroid plexus-CSF system could constitute an important pathway for neuroendocrine signalling in the brain, although clearcut evidence for such a role is still largely lacking.