PubMed Health⌕ Search

Biomedical subjects

V Ganapathy

Publications and source records attributed to V Ganapathy.

At least 145 records · Page 8Linked to original sources
PubMed1995

Molecular cloning of the human placental folate transporter.

We have isolated a cDNA clone from a human placental library which codes for a functional folate transporter (hFOLT). An RT-PCR product obtained from mouse intestinal mRNA using primers specific for the mouse folate transporter cDNA was used to screen the cDNA library. The hFOLT cDNA predicts a protein of 590 amino acids with twelve potential transmembrane domains. The amino acid sequence has 65% identity to the mouse and hamster folate transporters. When transfected into COS-1 and HeLa cells, the hFOLT cDNA causes a significant increase in the uptake of 5-methyltetrahydrofolate. The mRNA transcripts hybridizing to the hFOLT cDNA are detectable in the placenta and liver and also in several cell lines of human origin. The size of the principal transcript is 2.7 kb. This constitutes the first report on the cloning of a vitamin transporter from a human tissue.

Amino Acid Sequence↗
PubMed1995

Human placental monoamine transporters as targets for amphetamines.

OBJECTIVES: The use of amphetamine and its derivatives during pregnancy is known to have adverse effects on the outcome of pregnancy. These effects are at least partly a result of impairment of placental function caused by these abusable drugs. We hypothesized that the two monoamine transporters, namely, the serotonin transporter and the norepinephrine transporter, that are expressed in the human placenta are direct targets for these drugs. STUDY DESIGN: The interaction of amphetamine and methamphetamine with human placental serotonin and norepinephrine transporters was examined. Activity of the serotonin transporter was assessed by serotonin uptake in both maternal-facing brush border membrane vesicles isolated from normal term human placentas and in JAR choriocarcinoma cells. Activity of the norepinephrine transporter was assessed by dopamine uptake and nisoxetine binding in placental brush border membrane vesicles. RESULTS: Amphetamine and methamphetamine are potent inhibitors of the serotonin and norepinephrine transporters expressed in the human placenta. The inhibitory potency of amphetamine is greater than that of methamphetamine. In each case, the S(+)diastereoisomer is more potent than the corresponding R(-)diastereoisomer. The sensitivity of the norepinephrine transporter to inhibition by these drugs is at least two orders of magnitude greater than that of the serotonin transporter. At concentrations known to occur in the plasma of users, these drugs cause a marked inhibition of the norepinephrine transporter. CONCLUSIONS: The results show that the norepinephrine transporter and, to a lesser extent, the serotonin transporter are cellular targets in the human placenta for the abusable drugs amphetamine and methamphetamine.

Amphetamines↗
PubMed1995

Identification of a renal cell line that constitutively expresses the kidney-specific high-affinity H+/peptide cotransporter.

In this study we describe for the first time the identification of a renal cell line that expresses the kidney-specific high-affinity H+/peptide cotransport system. The kidney cell line SKPT-0193 C1.2 was obtained by SV40 transformation of rat proximal tubular cells. The transport of the dipeptide glycylsarcosine (Gly-Sar) was studied in this cell line grown as a confluent monolayer on impermeable plastic supports. Uptake of the dipeptide was rapid and was stimulated sixfold by an inwardly directed H+ gradient, with optimal uptake occurring at an extracellular pH of 6.0. The uptake was markedly reduced by the protonophore carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone whether measured at pH 7.5 or 6.0. Intracellular acidification of the cells by NH4Cl prepulse also reduced the uptake of glycylsarcosine. The dipeptide uptake was found to be mediated by a high-affinity transport system with a Michaelis-Menten constant (Kt) of 67 +/- 2 microM and a maximal transport velocity of 1.20 +/- 0.02 nmol.10 min-1.mg protein-1. Studied over a concentration range of 5 microM to 5 mM, there was no evidence for a second saturable transport component. Di- and tripeptides, but not glycine, were strong inhibitors of glycylsarcosine uptake, indicating that these peptides also interact with the transport system with high affinity. Northern blot analysis of poly(A)+RNA from these cells using cDNA probes specific for the human intestinal peptide transporter (PEPT 1) or the human kidney-specific peptide transporter (PEPT 2) revealed that the transport system expressed in these cells is PEPT 2. It is concluded that the SKPT-0193 C1.2 cell line constitutively expresses the kidney-specific high-affinity H+/peptide cotransporter described in the proximal tubular epithelial cells of the normal kidney.

Animals↗
PubMed1995

H(+)-peptide cotransport in Madin-Darby canine kidney cells: expression and calmodulin-dependent regulation.

The transport of the dipeptide glycylsarcosine was studied in the kidney cell lines OK, LLC-PK1, and Madin-Darby canine kidney (MDCK), grown as confluent monolayers on impermeable plastic supports. Uptake of the dipeptide in OK and LLC-PK1 cells was slow, was not inhibited by other peptides, and was not influenced by an inwardly directed H+ gradient, indicating lack of expression of the H(+)-peptide cotransport system in these cells under our conditions. In contrast, uptake of the dipeptide in MDCK cells was rapid and was found to be stimulated by an inwardly directed H+ gradient. This stimulation was markedly reduced by the protonophore carbonyl cyanide p-trifluoromethoxy-phenylhydrazone. The H+ gradient-dependent uptake of glycylsarcosine was inhibited by dipeptides and tripeptides and by the beta-lactam antibiotic cephalexin but not by the amino acids glycine and leucine. The uptake was saturable and apparently occurred via a single transport system. The Michaelis-Menten constant for the system was 1.3 +/- 0.1 mM, and the maximal velocity was 13.3 +/- 0.7 nmol.30.min-1.mg protein-1. Treatment of MDCK cells with the calmodulin antagonists N-(6-aminohexyl)-5-chloro-1-napthalenesulfonamide (W-7), CGS-9343B, or calmidazolium inhibited the glycylsarcosine uptake by 40-50% in a time- and dose-dependent manner. In contrast, the uptake of alanine, leucine, glucose, and taurine was found to be stimulated by treatment with W-7. Kinetic analysis revealed that the inhibition of the peptide transport activity was mainly associated with a decrease of the maximal velocity of the system.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Regulation of taurine transport by Escherichia coli heat-stable enterotoxin and guanylin in human intestinal cell lines.

The human colon carcinoma cell lines Caco-2 and HT-29 take up taurine actively. Treatment of Caco-2 cells with Escherichia coli heat-stable enterotoxin (STa) or with guanylin inhibited taurine uptake by approximately 40%. In contrast, neither STa nor guanylin changed the uptake of taurine in HT-29 cells. The inhibition in Caco-2 cells was associated with a decrease in the maximal velocity as well as in the affinity of the transporter. STa caused a 21-fold increase in guanosine 3',5'-cyclic monophosphate (cGMP) levels in Caco-2 cells with no change in cAMP levels. Neither cGMP nor cAMP levels were affected by STa treatment in HT-29 cells. Experiments with protein kinase inhibitors suggested that protein kinase A may mediate the observed effects of STa on taurine uptake. In accordance with this suggestion, treatment of Caco-2 cells with cholera toxin, which elevated intracellular cAMP levels, was found to inhibit taurine uptake. The steady state levels of the taurine transporter mRNA transcripts were not altered as a result of STa treatment. Studies with Caco-2 cells grown on permeable filters revealed that STa acts from the apical side. The taurine uptake from the apical side was inhibited by STa, but the taurine uptake from the basolateral side remained unaffected. It is suggested that the activity of the intestinal taurine transporter may be regulated by protein kinase A at a posttranslational level and that the intestinal absorption of taurine may be impaired during infection with enterotoxigenic strains of E. coli.

Alkaloids↗
PubMed1995

Cocaine-sensitive sigma-receptor and its interaction with steroid hormones in the human placental syncytiotrophoblast and in choriocarcinoma cells.

The expression and ligand binding characteristics of sigma-receptors in human placental syncytiotrophoblast and choriocarcinoma cells were investigated using haloperidol as a ligand. Haloperidol bound to purified placental brush border membranes with high affinity; the apparent dissociation constant for the process was about 3 nM. These binding sites were not related to dopamine (D2) and serotonin (5-HT2) receptors nor to serotonin and norepinephrine transporters. The ligands of sigma-receptors [3.g. (+)-3-(3-hydroxyphenyl)N-(1-propyl)piperidine, 1,3-di-(2-tolyl)guanidine, clorgyline, rimcazole, and dexromethorphan] were very potent in competing with haloperidol for the binding sites. The binding sites were detected not only in the brush border membrane, but also in intracellular membranes. The rank order of potency of various sigma-receptor ligands to inhibit haloperidol binding indicated that placental sigma-receptors belong to the sigma 1 subtype. Cocaine and its analog RTI-55 [2 beta-carbomethoxy-3 beta-(4-iodophenyl-) tropane] inhibited the binding of haloperidol to placental membranes with appreciable potency. The steroid hormones, progesterone and testosterone, were also potent inhibitors, and the inhibition constant for progesterone was 0.3 microM, a concentration much smaller than that found in plasma during pregnancy. The inhibition was competitive. beta-Estradiol and a number of other steroids were relatively much weaker inhibitors than progesterone and testosterone. Phenytoin and neuropeptide-Y did not interact with sigma-receptors in placenta. The choriocarcinoma cell line JAR was also found to express sigma-receptors in the plasma membrane as well as in intracellular membranes. The characteristics of the receptors in this cell were qualitatively similar to those of the receptors in normal placenta, including subtype identity and interaction with cocaine and progesterone. Interestingly, however, all sigma-receptor ligands interacted with the receptors in the JAR cell with much higher affinity than with the receptors in normal placenta. It is concluded that the placental syncytiotrophoblast and choriocarcinoma cells express cocaine-sensitive sigma-receptors and that progesterone is most likely an endogenous ligand for these receptors.

Choriocarcinoma↗
PubMed1995

Cyclic AMP-dependent up-regulation of the taurine transporter in a human retinal pigment epithelial cell line.

This investigation was undertaken to study the role of cAMP in the regulation of the taurine transporter expressed in a human retinal pigment epithelial (HRPE) cell line. Treatment of the HRPE cells with cholera toxin for 24 h was found to stimulate the taurine transporter activity, as measured by taurine transport into the cells in the presence of NaCl, to a significant extent. The stimulation was 50-60% at 100 ng/ml cholera toxin. This stimulation was specific to the taurine transporter since the transport of two other amino acids (leucine and alanine), which are not substrates for the taurine transporter, was not affected by cholera toxin under similar conditions. Exposure of the cells to cholera toxin for a time period > 4 h was needed to elicit the stimulatory effect. The cholera toxin-induced stimulation of the taurine transporter activity was associated with an increase in the maximal velocity of the transport system. The affinity of the transporter for taurine was not altered by the treatment. The stimulatory effect was markedly blunted when the treatment of the cells with cholera toxin was done in the presence of actinomycin D, an inhibitor of transcription, or cycloheximide, an inhibitor of translation. The increase in the taurine transporter activity induced by cholera toxin was associated with a 2.6-fold increase in the steady state levels of the transporter mRNA. Measurement of cyclic nucleotides in control and cholera toxin-treated cells revealed that the toxin caused a 20-fold increase in the cellular levels of cAMP, the levels of cGMP remaining unaffected.(ABSTRACT TRUNCATED AT 250 WORDS)

Alanine↗
PubMed1994

Characterization of the glycine transport system GLYT 1 in human placental choriocarcinoma cells (JAR).

Transport of glycine in confluent monolayer cultures of JAR human placental choriocarcinoma cells was investigated. Glycine uptake in these cells was made up of two components, one being Na(+)-dependent with no requirement for Cl- and the other being dependent on Na+ as well as Cl-. Substrate specificity studies indicated that distinct transport systems were responsible for these two components. Alanine inhibited the Na(+)-dependent glycine uptake preferentially and the Na(+)- and Cl(-)-dependent glycine uptake represented > 95% of total uptake in the presence of 5 mM alanine. Competition experiments revealed that the Na(+)- and Cl(-)-dependent transport system exhibited a very narrow substrate specificity with affinity toward only glycine and its derivatives such as sarcosine, glycine methyl ester and glycine ethyl ester. These characteristics identify the transport system as GLYT 1. This system showed high affinity for glycine, with a Michaelis-Menten constant of 15 microM. The Na+:Cl-: glycine stoichiometry appeared to be 2:1:1. Treatment of JAR cells with calmodulin antagonists resulted in the inhibition of the transport function of GLYT 1 and this inhibition was solely due to a decrease in the maximal velocity of the system with no change in the substrate affinity. It is concluded that the placental choriocarcinoma cell line JAR expresses robust activity of the glycine transporter GLYT 1 and that the activity of this transporter is under the regulation of calmodulin-dependent cellular processes.

Alanine↗
PubMed1994

Selective expression of the high-affinity isoform of the folate receptor (FR-alpha) in the human placental syncytiotrophoblast and choriocarcinoma cells.

The folate receptor (FR), an essential component in the process of folate uptake in various cells, is known to exist in three isoforms, FR-alpha, FR-beta and FR-gamma, with differential tissue expression. Transfer of folate across the human placenta from mother to fetus involves participation of a folate receptor expressed in the syncytiotrophoblast, but the isoform identity of this receptor has not been established. Based on the tissue/cell type from which these isoforms have been cloned, it is currently believed that FR-alpha is the isoform expressed in adult tissues whereas FR-beta is the isoform expressed in fetal tissues including placenta. The present study, undertaken primarily to establish the isoform identity of the FR expressed in the placental syncytiotrophoblast, does not support this currently prevailing nomenclature. Reverse transcription coupled with polymerase chain reaction (RT-PCR) of total/poly(A)+ RNA from placenta, cultured trophoblast cells and JAR choriocarcinoma cells with primer pairs specific for either FR-alpha or FR-beta reveals that while both isoforms are detectable in the whole placental tissue, only FR-alpha is present in the normal trophoblast cells and in the choriocarcinoma cells. Northern analysis with probes designed to distinguish between the mRNA transcripts coding for these two isoforms corroborate the RT-PCR findings. Furthermore, the nucleotide sequences of the PCR products obtained from the trophoblast cells and JAR cells are identical to the nucleotide sequence of the FR-alpha cDNA. These studies establish that it is the FR-alpha isoform, and not the FR-beta isoform, which is selectively expressed in the placental trophoblast cells. FR-beta, which is known to be present in the placenta, most likely arises from the maternal decidua normally associated with this tissue.

Amino Acid Sequence↗
PubMed1994

Functional coupling between a bafilomycin A1-sensitive proton pump and a probenecid-sensitive folate transporter in human placental choriocarcinoma cells.

The mechanism of transport of 5-methyltetrahydrofolate, the predominant form of folate in human blood, was investigated in JAR human placental choriocarcinoma cells. Northern analysis revealed the presence of the folate receptor mRNA in these cells. Accumulation of 5-methyltetrahydrofolate in these cells was saturable and inhibited by other folate analogs. The transport of 5-methyltetrahydrofolate into the cytoplasm was decreased by the anion transport inhibitors probenecid and 4,4'-diisothiocyanostilbene 2,2'-disulfonic acid. The cytosolic transport was dependent on a transmembrane H+ gradient because NH4Cl and chloroquine which alkalinize acidic compartments in the cell and protonophores which dissipate transmembrane H+ gradients inhibited the transport. The inhibitors of receptor-mediated endocytosis, monodansylcadaverine and bacitracin, had no effect on the cytosolic transport nor on the accumulation. Bafilomycin A1, a specific inhibitor of the vacuolar type (V-type) H(+)- pump, caused a significant reduction in the cytosolic transport of 5-methyltetrahydrofolate, without affecting the binding of the vitamin to its membrane bound receptor. It is concluded that (a) the JAR cells transport 5-methyltetrahydrofolate via a specific probenecid-sensitive folate transporter, (b) the transporter is driven by a transmembrane H+ gradient, and (c) the H+ gradient involved in this process is generated by a bafilomycin A1-sensitive V-type H(+)-pump present in the plasma membrane. The results strongly suggest that the transport of folate in these cells occurs by potocytosis involving a functional coupling between the folate receptor, the folate transporter and the H+ pump.

Anti-Bacterial Agents↗
PubMed1994

Calmodulin-dependent modulation of pH sensitivity of the amino acid transport system L in human placental choriocarcinoma cells.

The JAR human placental choriocarcinoma cells express the amino acid transport system L. The activity of this system is Na(+)-independent and is stimulated by acidic extracellular pH. Treatment of cells with the calmodulin antagonist CGS 9343B results in a marked stimulation of the system L activity. At a CGS 9343B concentration of 50 microM, the stimulation of activity measured at pH 7.5 is about 75-100%. This effect is not blocked by cycloheximide, actinomycin D, colchicine or cytochalasin D suggesting that the stimulation is not due to de novo synthesis of the carrier protein or recruitment of the carrier protein from an intracellular pool. The stimulatory effect of CGS 9343B is reproducible with other calmodulin antagonists. Treatment with CGS 9343B significantly modifies pH sensitivity of the system. The stimulatory effect of H+ is markedly reduced in treated cells compared to control cells. The stimulation of activity at pH 5.5 vs. pH 7.5 is 55% in control cells but only 8% in treated cells. Similarly, the stimulatory effect of CGS 9343B is reduced by H+. The stimulation of activity seen with 50 microM CGS 9343B is 80% at pH 8.0, but only 26% at pH 5.5. In addition, H+ and CGS 9343B affect the kinetic parameters of system L in a similar manner, the stimulation in both cases being primarily due to an increase in the maximal velocity. The apparent competitive nature between the effects of H+ and CGS 9343B is also observed with other calmodulin antagonists. These results show that the transport function and pH sensitivity of the amino acid transport system L in placental choriocarcinoma cells are modulated by calmodulin by processes which do not involve de novo synthesis nor recruitment of the carrier protein.

Alanine↗
PubMed1994

Functional characterization and chromosomal localization of a cloned taurine transporter from human placenta.

A cDNA clone highly related to the rat brain taurine transporter has been isolated from a human placental cDNA library. Transfection of this cDNA into HeLa cells results in a marked elevation of taurine transport activity. The activity of the cDNA-induced transporter is dependent on the presence of Na+ as well as Cl-. The Na+/Cl-/taurine stoichiometry for the cloned transporter is 2:1:1. The transporter is specific for taurine and other beta-amino acids, including beta-alanine, and exhibits high affinity for taurine (Michaelis-Menten constant approximately 6 microM). The clone consists of a coding region 1863 bp long (including the termination codon), flanked by a 376 bp-long 5' non-coding region and a 625 bp-long 3' non-coding region. The nucleotide sequence of the coding region predicts a 620-amino acid protein with a calculated M(r) of 69,853. Northern-blot analysis of poly(A)+ RNA from several human tissues indicates a complex expression pattern differing across tissues. The principal transcript, 6.9 kb in size, is expressed abundantly in placenta and skeletal muscle, at intermediate levels in heart, brain, lung, kidney and pancreas and at low levels in liver. Cultured human cell lines derived from placenta (JAR and BeWo), intestine (HT-29), cervix (HeLa) and retinal pigment epithelium (HRPE), which are known to possess Na(+)- and Cl(-)-coupled taurine transport activity, also contain the 6.9 kb transcript. Somatic cell hybrid and in situ hybridization studies indicate that the cloned taurine transporter is localized to human chromosome 3 p24-->p26.

Amino Acid Sequence↗
PubMed1994

Calmodulin-dependent regulation of the catalytic function of the human serotonin transporter in placental choriocarcinoma cells.

We investigated the involvement of calmodulin-dependent cellular processes in the regulation of the human serotonin transporter in placental choriocarcinoma cells. Treatment of JAR and BeWo cells with the selective calmodulin antagonist 1,3-dihydro-1-[1-((4-methyl-4H, 6H-pyrrolo[1,2-a][4,1]-benzoxapin-4-yl)-methyl)-4-piperindinyl+ ++]- 2H-benzimidazol-2-one (CGS93-43B (CGS)) for 1 h decreased the imipramine-sensitive serotonin transport activity markedly. The inhibitory effect was specific and was reproducible with other calmodulin antagonists. The basal serotonin transport activity as well as the activity that was stimulated by cholera toxin were inhibited to a similar extent. The CGS-induced inhibition was accompanied by a decrease in the maximal velocity and in the affinities of the transporter for Na+ and Cl- and an increase in the affinity for serotonin. There was, however, no change in the Na+/Cl-/serotonin stoichiometry. The inhibition of the transport activity induced by the treatment of intact cells with CGS was observable in plasma membrane vesicles isolated from these cells. Treatment with CGS had no effect on steady state levels of the serotonin transporter mRNAs nor on the transporter density in the plasma membrane. We conclude that the serotonin transporter is regulated by calmodulin-dependent processes in human placental choriocarcinoma cells involving posttranslational modification, most likely phosphorylation/dephosphorylation, of the transporter protein.

Alanine↗
PubMed1994

Expression cloning of a mammalian proton-coupled oligopeptide transporter.

In mammals, active transport of organic solutes across plasma membranes was thought to be primarily driven by the Na+ gradient. Here we report the cloning and functional characterization of a H(+)-coupled transporter of oligopeptides and peptide-derived antibiotics from rabbit small intestine. This new protein, named PepT1, displays an unusually broad substrate specificity. PepT1-mediated uptake is electrogenic, independent of extracellular Na+, K+ and Cl-, and of membrane potential. PepT1 messenger RNA was found in intestine, kidney and liver and in small amounts in brain. In the intestine, the PepT1 pathway constitutes a major mechanism for absorption of the products of protein digestion. To our knowledge, the PepT1 primary structure is the first reported for a proton-coupled organic solute transporter in vertebrates and represents an interesting evolutionary link between prokaryotic H(+)-coupled and vertebrate Na(+)-coupled transporters of organic solutes.

Amino Acid Sequence↗
PubMed1994

Expression and protein kinase C-dependent regulation of peptide/H+ co-transport system in the Caco-2 human colon carcinoma cell line.

The characteristics of the transport of the dipeptide glycylsarcosine were studied in the human colon carcinoma cell line Caco-2 grown as a monolayer on impermeable plastic support. Transport of glycylsarcosine in these cells was found to be Na(+)-independent, but was stimulated by an inwardly directed H+ gradient. This H(+)-dependent transport of glycylsarcosine was inhibited by di- and tri-peptides and also by the beta-lactam antibiotic cephalexin, but was unaffected by the amino acids glycine and leucine. The transport system exhibited a Michaelis-Menten constant (Kt) of 1.1 +/- 0.1 mM for glycylsarcosine. The specific activity of the transport system in this cell line was found to be maximal when the cultures were confluent. Treatment of the cells with phorbol esters which activate protein kinase C resulted in a significant inhibition of the transport system. This inhibition was specific and could be blocked if treatment was done in the presence of staurosporine, an inhibitor of protein kinase C. Kinetic analysis revealed that the inhibition was associated with a decrease in the maximal velocity, the Kt remaining unaffected. The phorbol-ester-induced inhibition of the peptide-transport system was not prevented by co-treatment with cycloheximide, an inhibitor of cellular protein synthesis. In addition, there was no change in the intracellular pH following treatment with the phorbol ester, suggesting that the effect was not due to alterations in the transmembrane pH gradient. It is concluded that the peptide/H+ co-transport system, which is known to exist in the normal intestine, is expressed in Caco-2 cells and that the function of the transport system is under the regulatory control of protein kinase C.

Alkaloids↗
PubMed1994

A Na:H exchanger subtype mediates volume regulation in bovine corneal epithelial cells.

To identify a role for a Na:H (NHE) exchanger subtype in volume regulation in bovine corneal epithelium, we determined: 1. its sensitivity to inhibition by amiloride analogues 2. the effects of either Cl removal or hypertonicity on the intracellular pH. Our results suggest that volume regulatory responses elicited by stimulation of NHE-2 may help preserve epithelial barrier function in the face of increases in tear film osmolarity.

Amiloride↗
PubMed1994

Human placenta as a target organ for cocaine action: interaction of cocaine with the placental serotonin transporter.

The interaction of cocaine and its analog 2 beta-carbomethoxy-3 beta-(4-iodophenyl) tropane (RTI-55) with the human placental serotonin transporter was investigated. The function of the placental serotonin transporter was assayed using three different approaches: serotonin uptake in purified human placental brush border membrane vesicles, paroxetine binding in placental brush border membrane vesicles, and serotonin uptake in cultured human placental choriocarcinoma cells. The interaction of cocaine and RTI-55 with the transporter was studied by determining the effects of these compounds on the transporter function. Cocaine and RTI-55 were found to be potent inhibitors of the transporter in all three approaches. The inhibition was competitive in nature in all cases. The inhibition constant (Ki) for cocaine was not influenced significantly by the duration of time allowed for the compound to interact with the transporter. In contrast, the inhibition constant for RTI-55 was influenced markedly by this parameter. The longer the time allowed for interaction of RTI-55 with the transporter, the smaller was the Ki value. These results suggest that the association kinetics for the interaction of cocaine and RTI-55 with the placental serotonin transporter are significantly different. When equilibrium interaction was allowed, cocaine inhibited the function of the transporter with a Ki of 0.09 microM. It is concluded that cocaine and its analog RTI-55 are potent inhibitors of the function of the serotonin transporter that is expressed in the normal human placenta and in cultured human placental choriocarcinoma cells. Since the reported values for cocaine concentration in the blood of cocaine users are several-fold higher than the inhibition constant for cocaine, the present study strongly suggests that the function of the placental serotonin transporter may be severely impaired by maternal use of cocaine during pregnancy. These findings may be relevant to fetal and placental complications of cocaine abuse during pregnancy.

Carrier Proteins↗