Biomedical subjects

N A Khan

Publications and source records attributed to N A Khan.

At least 37 records · Page 2Linked to original sources

PubMed2001

Docosahexaenoic acid modulates phorbol ester-induced activation of extracellular signal-regulated kinases 1 and 2 in NIH/3T3 cells.

Phosphorylation of extracellular signal-regulated kinases (ERK1/ERK2) has been implicated in cell proliferation of mammalian cells. In the present study, we investigated the role of docosahexaenoic acid (DHA) in the modulation of ERK1/ERK2 phosphorylation, stimulated either with phorbol 12-myristate 13-acetate (PMA) or transforming growth factor-alpha (TGFalpha) in NIH/3T3 cells. We observed that both PMA and TGFalpha induced ERK1/ERK2 phosphorylation within 5 min of stimulation. PMA acts upstream of MEK and via activation of protein kinase C (PKC), as GF109203X, a potent PKC inhibitor, and U0126, a MEK inhibitor, abolished its actions on ERK1/ERK2 phosphorylation. TGFalpha did not act via PKC because GF109203X failed to curtail the degree of ERK1/ERK2 phosphorylation in these cells. DHA alone failed to induce the phosphorylation of these mitogen-activated protein (MAP) kinases; however, this fatty acid significantly curtailed the PMA- but not TGFalpha-induced MAP kinase enzyme activity and phosphorylation in NIH/3T3 cells. Furthermore, we observed that DHA significantly inhibited PMA-induced translocation of two PKC isoforms, PKC alpha and PKC epsilon, from cytosol to plasma membrane. Interestingly, DHA failed to inhibit the PMA-induced translocation PKC delta isoform in these cells. Furthermore, DHA decreased PMA-induced proliferation of NIH/3T3 cells. In this study, we show for the first time that DHA inhibits MAP kinase ERK1/ERK2) activation and proliferation of NIH/3T3 cells via its inhibitory action on PKC alpha and epsilon isoforms.

3T3 Cells↗

PubMed2001

Inhibition of diabetes in NOD mice by human pregnancy factor.

Clinical symptoms of Th1 mediated autoimmune diseases regress in many patients during pregnancy. A prominent feature of pregnancy is the presence of human chorionic gonadotrophin hormone (hCG) in blood and urine. In this report we tested the effect of clinical grade hCG (c-hCG) on the development of diabetes, a Th1 mediated autoimmune disease, in nonobese diabetic (NOD) mice. We show that treatment of NOD mice with c-hCG before the onset of clinical symptoms lowered the increased blood glucose levels, reversed the established inflammatory infiltrate of pancreatic tissue, and profoundly inhibited the development of diabetes for prolonged time. c-hCG also induced profound inhibition of the functional activity (i.e. production of IFN-gamma) of Th1 cells. Transfer of spleen cells from c-hCG-treated NOD mice into immunocompromised NOD.SCID mice inhibited the development of diabetes in these otherwise nontreated mice. This shows that the treatment of the donor NOD mice induced persistent changes in the immune system. The antidiabetic activity of c-hCG was not caused by heterodimeric hCG or its subunits. Instead, this antidiabetic activity resided in a fraction of c-hCG preparation that contains a 400-2000 Dalton natural (immuno) modulatory pregnancy factor (NMPF).

Animals↗

PubMed2001

Dietary (n-3) polyunsaturated fatty acids exert antihypertensive effects by modulating calcium signaling in T cells of rats.

After 10 wk of feeding an experimental diet enriched with (n-3) polyunsaturated fatty acids (PUFA), i.e., eicosapentaenoic acid [EPA, 20:5(n-3)] and [DHA, 22:6(n-3)] (EPAX), blood pressure in spontaneously hypertensive rats (SHR), but not in normotensive Wistar-Kyoto (WKY) rats was reduced relative to rats fed an unsupplemented control diet. Concanavalin A-stimulated T-cell proliferation was diminished in both strains of rats fed the PUFA/EPAX diet. The experimental diet lowered secretion of interleukin-2 in SHR, but not in WKY rats compared with rats fed the control diet. To determine whether there was a defect in calcium homeostasis in T cells during hypertension, we employed the following agents: caffeine, which recruits calcium from the cytosolic Ca(2+)-induced Ca(2+)-release pool; ionomycin, which at low concentrations opens calcium channels; and thapsigargin (TG), which mobilizes [Ca(2+)]i from the endoplasmic reticulum (ER) pool. Caffeine-induced increases in [Ca(2+)]i were not modified by the PUFA/EPAX diet. The ionomycin-induced increases in [Ca(2+)]i in T cells from SHR were greater than in those from WKY rats; consumption of the PUFA/EPAX diet did not modify Ca(2+) influx in cells of either strain. The TG-induced increases in [Ca(2+)]i in T cells from SHR were greater than those in cells from WKY rats. Interestingly, consumption of the experimental diet reduced TG-evoked increases in [Ca(2+)]i in T cells from SHR and increased those in T cells from WKY rats, indicating that the PUFA/EPAX diet could reverse the calcium mobilization from the ER pool in T cells. These results suggest that (n-3) PUFA exert antihypertensive effects and modulate T-cell calcium signaling during hypertension in rats.

Animals↗

PubMed2001

Implication of acyl chain of diacylglycerols in activation of different isoforms of protein kinase C.

We synthesized diacylglycerols (DAGs) containing omega-6 or omega-3 polyunsaturated fatty acids [i.e., 1-stearoyl-2-arachidonoyl-sn-glycerol (SAG), 1-stearoyl-2-docosahexaenoyl-sn-glycerol (SDG), and 1-stearoyl-2-eicosapentaenoyl-sn-glycerol (SEG)] and assessed their efficiency on activation of conventional (alpha, beta I, gamma) and novel (epsilon, delta) protein kinase C (PKC). SAG exerted significantly higher stimulatory effects than SDG and SEG on activation of PKC alpha and PKC delta. Activation of PKC beta I by SEG and SDG was higher than that by SAG. Activation of PKC gamma did not differ significantly among DAG molecular species. Addition of SAG to assays containing SEG and SDG exerted additive effects on activation of alpha and epsilon, but not on beta I and gamma, isoforms of PKC. SDG- and SEG-induced activation of PKC delta was significantly curtailed by the addition of SAG. Three DAG species significantly curtailed the PMA-induced activation of beta Iota, gamma, and delta, but not of alpha and epsilon, isoforms of PKC. Our study demonstrates for the first time that in vitro activation of different PKC isoenzymes vary in response to different DAG species, and one can envisage that this differential regulation may be responsible for their in vivo effects on target organs.

Diglycerides↗

PubMed2001

Precurarization and priming: a theoretical analysis of safety and timing.

UNLABELLED: The priming principle suggests that the onset of neuromuscular block may be accelerated if an intubating dose is preceded by a priming dose administered a few minutes earlier. We thought it would be instructive to use a pharmacodynamic/pharmacokinetic model to estimate the risk associated with different priming doses and intervals. In any normal population, there is wide variability in the response to neuromuscular blocking drugs. For most relaxants, the coefficient of variation for the 50% effective dose (ED(50)) approximates 20%-25%. Thus, 1 patient in 50 (-2.05 SD) may have an ED(50) only half of the commonly cited value. By using published pharmacodynamic/pharmacokinetic data, we calculated the effect of administering 10%, 20%, or 30% of the ED(95) on the response of the adductor pollicis muscle in a population normally distributed with respect to drug sensitivity. A dose equivalent to 10% of the ED(95) will rarely produce a measurable neuromuscular effect. As this dose is increased, the potential for clinical weakness rapidly escalates. In 1 in 50 individuals, the usual recommendation of 10% of the intubation dose will produce measurable neuromuscular depression. For vecuronium, the optimal priming interval is 5 min. The safety and dependability of the priming principle is very much subject to the laws of probability. IMPLICATIONS: When using the priming principle to accelerate the onset of neuromuscular block, the initial dose should not exceed 10% the drug's ED(95). For drugs other than rocuronium, the optimal priming interval is not <5 min.

Androstanols↗

PubMed2001

Eicosapentaenoic acid and docosahexaenoic acid modulate MAP kinase (ERK1/ERK2) signaling in human T cells.

This study was conducted on human Jurkat T cell lines to elucidate the role of EPA and DHA, n-3 PUFA, in the modulation of two mitogen-activated protein (MAP) kinases, that is, extracellular signal-regulated kinases 1 and 2 (ERK1 and ERK2). The n-3 PUFA alone failed to induce phosphorylation of ERK1/ERK2. We stimulated the MAP kinase pathway with anti-CD3 antibodies and phorbol 12-myristate 13-acetate (PMA), which act upstream of the MAP kinase (MAPK)/ERK kinase (MEK) as U0126, an MEK inhibitor, abolished the actions of these two agents on MAP kinase activation. EPA and DHA diminished the PMA- and anti-CD3-induced phosphorylation of ERK1/ERK2 in Jurkat T cells. In the present study, PMA acts mainly via protein kinase C (PKC) whereas anti-CD3 antibodies act via PKC-dependent and -independent mechanisms. Furthermore, DHA and EPA inhibited PMA-stimulated PKC enzyme activity. EPA and DHA also significantly curtailed PMA- and ionomycin-stimulated T cell blastogenesis. Together these results suggest that EPA and DHA modulate ERK1/ERK2 activation upstream of MEK via PKC-dependent and -independent pathways and that these actions may be implicated in n-3 PUFA-induced immunosuppression.

Antibodies↗

PubMed2000

Influence of nitric oxide synthase II gene disruption on tumor growth and metastasis.

The relationship between nitric oxide (NO) synthase II (NOS II) expression and the metastatic ability of tumor cells is inconclusive. We determined the role of host NOS II expression in the growth and metastasis of the B16-BL6 murine melanoma and M5076 murine ovarian sarcoma cell lines. The cells were either s.c. or i.v. injected into syngeneic wild-type (NOS H+/+) and NOS II-null (NOS H-/-) C57BL/6 mice. Both cell lines produced slightly larger s.c. tumors in NOS H-/- mice than in NOS II+/+ mice. However, B16- BL6 cells produced more and larger experimental lung metastases in NOS II+/+ mice than in NOS II-/- mice, whereas M5076 cells produced fewer and smaller experimental lung metastases in NOS II+/+ mice than in NOS II-/- mice. After activation with IFN-gamma and lipopolysaccharide, macrophages isolated from NOS II+/+ C57BL/6 mice produced NO-dependent cytotoxicity in sarcoma cells, whereas macrophages from NOS II-/- C57BL/6 mice did not. In contrast, activated macrophages produced little to no NO-mediated cytotoxicity in melanoma cells. Immunostaining analyses indicated that NOS II expression was apparent in the metastases growing in NOS H+/+ mice and correlated with increased cell proliferation in B16-BL6 lung metastases but with decreased cell proliferation in M5076 liver metastases. Our data suggest that disruption of host NOS II expression enhanced the growth and metastasis of NO-sensitive tumor cells but suppressed the metastasis of NO-resistant tumor cells, proposing that host-derived NO may differentially modulate tumor progression.

Animals↗

PubMed2000

Use of unconventional methods of therapy by cancer patients in Pakistan.

Most of the studies related to the use of unconventional methods of therapy by cancer patients have been carried out in the developed countries. This study was conducted to ascertain the frequency, type, and duration of use of unconventional methods of therapy by cancer patients in Pakistan. We also wanted to identify individuals who are most likely to use these methods and to compare the findings with those reported from the developed countries. Between 1 April and 30 May 1994, all patients with histologically proven cancer who visited the oncology unit were interviewed. A printed questionnaire with questions and options was used as an interview guide. Informed consent was obtained. One hundred and ninety-one patients were interviewed, on average, for 25 minutes each. Use of unconventional methods of therapy by cancer patients was widespread (54.5% of all patients). The majority (83.7%) were influenced by family members to use these methods. Traditional herbal medicines (70.2%) and homeopathy (64.4%) were the most commonly employed methods. Thirty-six percent of the users employed these methods before receiving any conventional therapy. Only 15% used these methods after conventional therapeutic options had been exhausted. Patients generally perceived these methods as useful, non-toxic and inexpensive. Age, marital status, socio-economic background, education level and status of underlying neoplasm did not influence the frequency of use of unconventional methods. The use, however, was influenced by gender, family size, and type of underlying malignancy. Patients aware of their diagnosis were less likely to use these methods. This study suggests that use of unconventional methods by cancer patients in Pakistan is widespread. Unlike western countries, these methods are often employed before receiving any conventional therapy. This probably results in a significant delay which can be expected to adversely influence the subsequent disease management and survival. Public education, reduction of cost and easy availability of conventional therapy may be helpful in reducing the use of methods which otherwise may have no proven value.

Adolescent↗

PubMed2000

Yield and costs of screening growth-retarded infants for torch infections.

Many infants with intrauterine growth retardation (IUGR) are screened for TORCH infections. The yield and costs of such a practice may not be justifiable. Medical charts of infants with IUGR who had a workup for toxoplasmosis, other (infections), rubella, cytomegalovirus (infection), and herpes (simplex) (titer) (TORCH) infections were reviewed for the presence of clinical findings, laboratory and head ultrasound abnormalities associated with intrauterine infections. Maternal charts and reports of placental pathology were reviewed for identifying maternal illnesses and placental causes associated with IUGR. Seventy-five out of 182 infants (41%) with IUGR had a workup for TORCH infection. Maternal conditions associated with IUGR included: pregnancy-induced hypertension (19%), tobacco use (43%), alcohol abuse (21%), illicit drug use (24%), chronic hypertension, diabetic vasculopathy or collagen vascular disease (12%), and multiple gestation (3%). Placental pathology was available in 53/75 cases. Thirty-six of fifty-three (67%) placentae had abnormalities associated with IUGR: placental infarcts (22 of 36), vasculitis/villitis (15 of 36), placenta previa (1 of 36), abruptio placenta (2 of 36), and velamentous insertion of umbilical cord (1 of 36). Clinical findings among infants included hepatosplenomegaly, cataract or rash (1 of 75), thrombocytopenia and/or neutropenia and/or direct hyperbilirubinemia (11 of 75). Seven out of 75 infants had dysmorphic features. None of the infants (0 of 75) had positive IgM titers for toxoplasma, rubella, cytomegalovirus (CMV), or herpes simplex virus (HSV). No infants (0 of 43) had elevated total IgM titers; one infant (1 of 57) had a positive urine culture for CMV. One infant had evidence of calcifications on head ultrasound and a second infant had hydrocephalus (2 of 43). The costs associated with workup for TORCH infections among 75 infants included: TORCH titers determination: $17,816, total IgM titers: $1318, urine culture for CMV: $5734, and head ultrasound: $28,165. The yield of workup for TORCH infection among infants with IUGR is poor and does not justify the incurred costs.

Adult↗

PubMed2000

Isolation of Acanthamoeba-specific antibodies from a bacteriophage display library.

Acanthamoeba causes opportunistic eye infections in humans, which can lead to severe keratitis and may ultimately result in blindness. Current methods for identifying this organism rely on culture and microscopy. In this paper, we describe the isolation of antibody fragments that can be used for the unequivocal identification of Acanthamoeba. A bacteriophage antibody display library was used to isolate antibody fragments that bind specifically to Acanthamoeba. Individual clones were studied by enzyme-linked immunosorbent assay, flow cytometry, and immunofluorescence. Four antibody clones that specifically bind to Acanthamoeba spp. were identified.

Acanthamoeba↗

PubMed2000

Proteases as markers for differentiation of pathogenic and nonpathogenic species of Acanthamoeba.

Acanthamoeba keratitis is a vision-threatening infection caused by pathogenic species of the genus Acanthamoeba. Although not all Acanthamoeba spp. can cause keratitis, it is important to differentiate pathogenic species and isolates from nonpathogens. Since extracellular proteases may play a role in ocular pathology, we used colorimetric, cytopathic, and zymographic assays to assess extracellular protease activity in pathogenic and nonpathogenic Acanthamoeba. Colorimetric assays, using azo-linked protein as a substrate, showed extracellular protease activity in Acanthamoeba-conditioned medium and differentiated pathogenic and nonpathogenic Acanthamoeba. Monolayers of immortalized corneal epithelial cells in four-well plates were used for cytopathic effect (CPE) assays. Pathogenic Acanthamoeba isolates exhibited marked CPE on immortalized corneal epithelial cells, while nonpathogenic isolates did not exhibit CPE. Protease zymography was performed with Acanthamoeba-conditioned medium as well as with Acanthamoeba- plus epithelial-cell-conditioned medium. The zymographic protease assays showed various banding patterns for different strains of Acanthamoeba. In pathogenic Acanthamoeba isolates, all protease bands were inhibited by phenylmethylsulfonyl fluoride (PMSF), suggesting serine type proteases, while in nonpathogenic strains only partial inhibition was observed by using PMSF. The pathogenic Acanthamoeba strains grown under typical laboratory conditions without epithelial cells exhibited one overexpressed protease band of 107 kDa in common; this protease was not observed in nonpathogenic Acanthamoeba strains. The 107-kDa protease exhibited activity over a pH range of 5 to 9.5.

Acanthamoeba↗

PubMed2000

Regulation of calcium signalling by docosahexaenoic acid in human T-cells. Implication of CRAC channels.

We elucidated the role of docosahexaenoic acid (DHA) on the increases in free intracellular calcium concentrations, [Ca(2+)]i, in human (Jurkat) T-cell lines. DHA evoked an increase in [Ca(2+)]i in a dose-dependent manner in these cells. Anti-CD3 antibody, known to stimulate increases in Ca(2+) from endoplasmic reticulum (ER) via the production of inositol trisphosphate, also evoked increases in [Ca(2+)]i in Jurkat T-cells. We also used thapsigargin which inhibits Ca(2+)-ATPase of the ER and, therefore, increases Ca(2+) in the cytosol. Interestingly, addition of DHA during the thapsigargin-induced peak response exerted an additive effect on the increases in [Ca(2+)]i in human T-cells, indicating that the mechanisms of action of these two agents are different. However, the DHA-induced calcium response was not observed when this agent was added during the anti-CD3-induced calcium peak, though its addition resulted in a prolonged and sustained calcium response as a function of time, suggesting that DHA recruits calcium, in part, from the ER pool and the prolonged response may be due to Ca(2+) influx. In the medium containing 0% Ca(2+), the DHA-evoked response on the increases in [Ca(2+)]i was significantly curtailed as compared to that in 100% Ca(2+) medium, supporting the notion that the response of the DHA is also due, in part, to the opening of calcium channels. Furthermore, preincubation of cells with tyrphostin A9, an inhibitor of Ca(2+) release-activated Ca(2+) (CRAC) channels also significantly curtailed the DHA-induced sustained response on the increases in [Ca(2+)]i in these cells. These results suggest that DHA induces an increase in [Ca(2+)]i via the ER pool and the opening of CRAC channels in human T-cells.

Antibodies↗

PubMed1999

Ionotrophic 5-hydroxytryptamine type 3 receptor activates the protein kinase C-dependent phospholipase D pathway in human T-cells.

The present study was undertaken to investigate the role of the 5-hydroxytryptamine (5-HT) ionotrophic receptor 5-HT(3) in the activation of human Jurkat T-cells. 5-HT and 2-methyl-5-HT (2Me-5-HT), an agonist of the 5-HT(3) receptor, induced increases in intracellular free Na(+) concentrations, [Na(+)](i), via opening of the ionotrophic receptor in these cells. These two serotonergic (5-hydroxytryptaminergic) agents potentiated phytohaemagglutinin (PHA)-induced T-cell activation. However, they failed to potentiate dioctanoglycerol-plus-ionomycin-stimulated T-cell blastogenesis. Interestingly, an inhibitor of protein kinase C (PKC), GF 109203X, curtailed significantly 5-HT and 2Me-5-HT-potentiated T-cell activation. These results demonstrate that the opening of the 5-HT(3) ionotrophic receptor is implicated in T-cell activation via the PKC pathway. Furthermore, 5-HT and 2Me-5-HT stimulated phospholipase D (PLD) activity, as measured by the production of phosphatidylethanol and phosphatidylbutanol at the expense of phosphatidic acid (PA). GF 109203X significantly curtailed the 5-HT- and 2Me-5-HT-induced PLD activity and T-cell activation. The PLD/PA pathway stimulated by these two serotonergic agents resulted in the production of 1,2-diacylglycerol (DAG) mass in Jurkat T-cells. These results altogether suggest that 5-HT and 2Me-5-HT potentiate T-cell activation via increases in [Na(+)](i) and the activation of the PKC-dependent PLD pathway.

Cell Cycle↗

PubMed1999

5-HT3 receptor-channels coupled with Na+ influx in human T cells: role in T cell activation.

The study was conducted on a human (Jurkat) T cell line, loaded with a Na+ fluorescent probe, SBFI/AM. Serotonin and an agonist of 5-HT3 receptor-channels, 2-methyl-5HT, evoked Na+ influx, whereas the agonists of other serotonergic receptor subtypes, i.e., 5-HT1A and 5-HT1B receptors, failed to induce Na+ influx in these cells. By using 3H-BRL43694, an agonist of 5-HT3 receptor-channels, we characterized 5-HT3 lymphocyte receptors which exhibited a density (Bmax) of 300 +/- 20 fmol/10(6) cells and a Kd of 30 nM in Jurkat T cells. The T-cell 5-HT3 receptor-channel is not regulated either by the protein kinase C or by the free intracellular calcium concentrations as the agents known to activate the PKC and to induce increases in intracellular free calcium concentrations failed to influence the free intracellular Na+ concentrations, [Na+]i, in these cells. Furthermore, an increase in [Na+]i, induced by 2-methyl-5HT, via 5-HT3 receptor-channels seems to stimulate T-cell activation by facilitating the progression of T cells from S to G2/M phase of the cell cycle.

8-Hydroxy-2-(di-n-propylamino)tetralin↗

PubMed1999

Methemoglobinemia induced by topical anesthesia: a case report and review.

Topical anesthetic drugs are widely used by clinicians during hospital and outpatient procedures and are also available to the public in a variety of over-the-counter preparations. Although generally safe, they may cause potentially life-threatening methemoglobinemia. We describe a patient who developed repeated episodes of severe methemoglobinemia after administration of topical Cetacaine spray (a proprietary mixture of benzocaine, tetracaine, and butamben) employed for pharyngeal anesthesia before endotracheal intubation, and briefly review the etiology and pathophysiology of this disorder. Cautious interpretation of oxyhemoglobin saturation values obtained by pulse oximetry or estimated from arterial blood gas analysis is crucial lest the diagnosis of severe methemoglobinemia and the resulting hypoxemia are overlooked. If necessary, the condition is usually readily corrected by intravenous administration of methylene blue.

4-Aminobenzoic Acid↗

PubMed1998

The anti-stress activity of a gem-containing Unani formulation against diverse stressors.

Drugs of mineral origin, especially gems, are extensively used in Tibb-e-Unani (Unani Medicine), both as single drugs and as compound formulations. But such drugs have not yet been adequately studied scientifically. Jawahir Mohra (JM) is one such, as yet unstudied, anti-stress Unani preparation, containing a few herbal and animal ingredients also. Therefore in the present study, a modified JM preparation was investigated for its anti-stress activity against physical, chemical and metabolic stimuli. The non-gem complement (NGC) of JM was also studied for action against physical stress. In albino rats stressed by swimming and subsequently tested for motor function by Rota rod (muscle coordination), activity wheel (forced motor activity) and photoactometer (spontaneous motor activity), JM treatment for 7 days produced a striking and significant increase in activity. The NGC also increased the activity significantly which was however less than JM. JM also produced a striking increase in cold swimming endurance and in the latency of post-anoxia convulsions, while pentylentetrazol (PTZ)-induced defecation and urination in an open field arena under continuous stimulation by intense light and sound was significantly decreased. Therefore, the present investigation indicates that the gem-containing Unani compound JM has significant anti-stress activity of a non-specific type against diverse stressors. This could be due to adaptogenic activity of the preparation. The study also shows that the gems in JM contribute significantly to its anti-stress activity.

Adaptation, Physiological↗

PubMed1997

5-Hydroxytryptamine-induced calcium-channel gating in rainbow trout (Oncorhynchus mykiss) peripheral blood lymphocytes.

The present study was conducted on peripheral blood lympho-cytes of rainbow trout (Oncorhynchus mykiss) to assess the role of 5-hydroxytryptamine (5-HT; 'serotonin') in calcium signalling. 5-HT-induced increases in intracellular free calcium concentrations, [Ca2+]i, and its action was mediated by 5-HT receptor subtype 3 (5-HT3), but not by 5-HT receptor subtype 1A (5-HT1A) or subtype 2 (5-HT2) in these cells. In Ca2+-containing medium (1 mM CaCl2), 5-HT and 2-methyl-5-HT (5-HT3 receptor agonist) induced increases in [Ca2+]i, whereas in Ca2+-free medium (0 Ca2+, 1 mM EGTA), these two agents failed to evoke increases in [Ca2+]i in these cells, demonstrating that 5-HT mobilizes Ca2+ from the extracellular environment. Furthermore, 5-HT-induced increases in [Ca2+]i are not contributed to by the intracellular endoplasmic reticulum (ER) pool, as thapsigargin, an agent that recruits Ca2+ from ER stores, had additive effects on 5-HT-induced [Ca2+]i responses in fish peripheral lymphocytes. 5-HT-induced increases in [Ca2+]i were mediated by 5-HT3 receptors via gating the calcium through L-type, but not N-type, calcium channels in trout lymphocytes.

8-Hydroxy-2-(di-n-propylamino)tetralin↗

PubMed1997

Identification of lymphocyte 5-HT3 receptor subtype and its implication in fish T-cell proliferation.

In the present study, we identified the serotonergic receptor of type 3 (5-HT3) on the lymphocytes of a teleost fish, Oncorhynchus mykiss. In the pharmacological studies on the binding of [3H]serotonin to membrane receptor sites, 2-methyl-5-HT, an agonist of 5-HT3 receptors, displaced the binding of [3H]serotonin to fish lymphocytes, indicating the presence of 5-HT3 receptors on these cells. The known antagonists of the mammalian 5-HT3 receptor, ICS-205-930 and metoclopramide, failed to displace [3H]serotonin binding to lymphocytes during the period of association equilibrium (8 min); however, these antagonists progressively displaced [3H]serotonin binding from 10 to 40 min of incubation. These results suggest that fish 5-HT3 lymphocyte receptors may differ pharmacologically from mammalian receptors. As mammalian 5-HT3 receptors are coupled with Na+ inward movements, we undertook a study on Na+ influx by using SBFI/AM, a fluorescent probe. In SBFI/AM loaded fish lymphocytes, 2-methyl-5-HT leaked Na+ inward movements. Prior incubation of lymphocytes for 30 min in the presence of 5-HT3 antagonists, ICS-205-930, metoclopramide and MDL-72222, curtailed significantly the Na+ influx evoked by 2-methyl-5-HT, demonstrating that Na+ is leaked into fish lymphocytes via the 5-HT3 receptor-channel whose functioning is blocked by these antagonists. Furthermore, 2-methyl-5-HT exerted immunosuppressive effects in a dose dependent manner on fish T-lymphocytes stimulated by phytohaemagglutinin (PHA). Serotonin and 2-methyl-5-HT blocked the cell cycle progression of PHA-stimulated T-cells from G0/G1 to S phase. The immunosuppressive effects of 2-methyl-5-HT on T-cells were partially reversed by the antagonists, metoclopramide and ICS-205-930; however, the latter antagonist at high concentrations synergized with the immunosuppressive effects of 2-methyl-5-HT. These results demonstrate that the fish lymphocyte 5-HT3 receptor, which may be pharmacologically different from mammalian receptor subtype, is functionally implicated in fish T-cell proliferation.

Animals↗