Arsenic poisoning in the Ganges delta.
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Arsenic↗
Biomedical subjects
S Lahiri
Publications and source records attributed to S Lahiri.
Chemoreceptor discharges and cytochrome redox changes of the rat carotid body: role of heme ligands.
In superfused in vitro rat carotid body, we recorded chemoreceptor discharges and the redox state of cytochromes simultaneously to identify the primary oxygen-sensing protein controlling transmitter release and electrical activity of the carotid sinus nerve. These parameters were tested under the influence of heme ligands such as oxygen, cyanide, 4-(2-aminoethyl)-benzenesulfonyl fluoride, and CO. During stimulation, there was an initial increase in discharge frequency followed by a decline or suppression of activity. Photometric changes lagged and were maintained as nerve activity decreased. Reducing mitochondrial cytochromes by cyanide or prolonged severe hypoxia, suppressed the chemoreceptor discharge. 4-(2-Aminoethyl)-benzenesulfonyl fluoride, a specific inhibitor of the phagocytic cytochrome b(558), also silenced the chemoreceptors after an initial excitation. CO increased the chemoreceptor discharge under normoxia, an effect inhibited by light, when the cytochromes were not reduced. When the discharges were depressed by severe hypoxia, exposure to light excited the chemoreceptors and the cytochromes were reduced. The rapidity of the chemosensory responses to light and lack of effect on dopamine release from type I cells led us to hypothesize that carotid body type I cells and the apposed nerve endings use different mechanisms for oxygen sensing: the nerve endings generate action potentials in association with membrane heme proteins whereas cytosolic heme proteins signal the redox state, releasing modulators or transmitters from type I cells.
Afferent Pathways↗
Chemosensory response to high pCO is blocked by cadmium, a voltage-sensitive calcium channel blocker.
In the dark, during normocapnic (pCO2=35 Torr, pHo=7.4) normoxia (pO2=100 Torr), high pCO (>300 Torr) causes Ca2+-dependent photolabile excitation of chemosensors in the carotid body (CB). We previously proposed that the source of this Ca2+ was the [Ca2+]i stores because CO would react only intracellularly. However, influx of extracellular Ca2+ was not excluded. Now, using perfused rat CB (n=6) in the presence of normal extracellular [Ca2+] we show that chemosensory response to CO (pCO approximately 550 Torr) in normoxic (pO2 approximately 100 Torr) normocapnia (pCO2 approximately 30 Torr, pH approximately 7.4) is completely but reversibly inhibited by Cd2+ (200 microM), a voltage-gated Ca2+ channel blocker. Thus, extracellular Ca2+ is necessary for excitatory chemosensory response to high pCO. Cd2+ block occurs in spite of an enhanced [Ca2+]i rise. This shows that Ca2+ rise alone is unable to release neurotransmitter and to elicit a chemosensory response. Therefore, as a corollary, we conclude that Cd2+ blocks the Ca2+ flux that is needed for vesicle-membrane fusion for neurotransmitter release and neural discharge.
Animals↗
Redox-dependent binding of CO to heme protein controls P(O2)-sensitive chemoreceptor discharge of the rat carotid body.
Simultaneous recordings of chemoreceptor discharge and redox state of cytochromes have been carried out on the rat carotid body in vitro under the influence of carbon monoxide (CO) in order to identify the primary oxygen sensor protein controlling transmitter release and electrical activity. CO excites in a photolabile manner chemoreceptor discharge under normoxic conditions and inhibits under hypoxic conditions probably by binding to heme proteins. We hypothesize that type I cells and adjacent nerve endings of the carotid body tissue have a different apparatus with oxygen sensing heme proteins to cooperate for the generation of peripheral chemoreceptor response. Transmitter release from type I cells might be established in a redox dependent manner whereas membrane potential of nerve endings might be controlled by a heme coupled to ion channels.
Animals↗
Separation of carrier free 151,152Tb produced in 16O irradiated lanthanum oxide matrix.
Charged particle activation of natural La2O3 with approximately 78.5 MeV 16O results in the formation of carrier free 151,152Tb isotopes in the matrix. The liquid cation exchanger, HDEHP, has effectively been utilised as an extractant in the quantitative separation of the activation products from the bulk target matrix of lanthanum oxide.
Cation Exchange Resins↗
High PCO does not alter pHi, but raises [Ca2+]i in cultured rat carotid body glomus cells in the absence and presence of CdC12.
We measured the effect of high PCO (500-550 Torr) on the pHi and [Ca2+]i in cultured glomus cells of adult rat carotid body (CB) as a test of the two models currently proposed for the mechanism of CB chemoreception. The metabolic model postulates that the rise in glomus cell [Ca2+]i, the initiating reaction in the signalling pathway leading to chemosensory neural discharge, is due to [Ca2+] release from intracellular Ca2+ stores. The membrane potential model postulates that the rise in [Ca2+]i comes from influx of extracellular Ca2+ through voltage-dependent Ca2+ channels (VDCC) of the L-type. High PCO did not change pHi at PO2 of 120-135 Torr, showing that CO-induced changes in [Ca2+]i are not due to changes in pHi. High PCO caused a highly significant rise in [Ca2+]i from 90+/-12 nM to 675+/-65 nM, both in the absence and in the presence of 200 microM CdCl2, a potent blocker of L-type VDCCs. This result is fully consistent with release of Ca2+ from glomus cell intracellular stores according to metabolic model, but inconsistent with influx of extracellular Ca2+ through VDCCs according to the membrane potential model.
Animals↗
Further characterization of stimulus interaction of cat carotid chemoreceptors.
The hypothesis that the maximal response to pCO2 of carotid body chemoreceptors would be the same regardless of pO2, if the receptor molecule behaves like a hemoglobin molecule, was investigated using single or a few fiber carotid body chemoreceptors in cats in vivo which were anesthetized and artificially ventilated. In one series, graded levels of CO2 inhalation in steady-state at p(a)O2 = 354 +/- 19 Torr showed a linear response from 1 to 20.1 +/- 2.3 imp/s for p(a)CO2 increase from 32 to 178 +/- 18 Torr, and at p(a)O2 of 48 +/- 3.8 Torr, from 3.8 to 18.6 +/- 1.7 imp/s for p(a)CO2 increase from 21 to 109 +/- 11 Torr, levelling off thereafter. In another series of multi-fiber preparation, close intra-arterial injection of blood plus saline containing pCO2 of about 270 Torr gave peak responses of 44 +/- 9, 42 +/- 6 and 42 +/- 7 imp/s at p(a)O2 of 40 +/- 4, 82 +/- 6 and 388 +/- 18 Torr, respectively. Thus, the chemosensory responses to p(a)CO2 reached the same level of maximal activity regardless of p(a)O2. Taken together, the maximal responses in both steady-state and transient-state to p(a)CO2 appeared to be the same at hypoxic and hyperoxic p(a)O2. This stimulus-response relationship of the receptor molecule is analogous to O2-CO2 interaction with hemoglobin molecule with a Bohr effect, reaching a saturation point at a finite pO2.
Acidosis↗
Anion exchanger and chloride channel in cat carotid body chemotransduction.
In order to test the hypothesis that carotid body (CB) chemoreception depends on the functions of anion channels and HCO3-/Cl- exchangers, we studied the effects of the anion channel blocker anthracene-9-carboxylic acid (9-ANC), the carbonic anhydrase inhibitor methazolamide, and the HCO3-/Cl- exchanger blocker 4,4 diisothiocyanatostilbene-2-2'disulfonic acid (DIDS) on the chemosensory discharges of cat CB, perfused-superfused in vitro at 36.5 +/- 0.5 degrees C, with a modified Tyrode solution. The chemosensory responses to hypoxia (PO2 approximately 50 Torr), hypercapnia (PCO2 approximately 60 Torr, pH = 7.10), nicotine (2-4 nmol) and NaCN (20-40 nmol) were recorded. 9-ANC (2 microM) and DIDS (10 microM) decreased the chemosensory baseline activity, and eliminated the initial peak responses to hypercapnia and hypoxia and increased the time to achieve it. Methazolamide (0.13 mM) did not alter the effect of 9-ANC. The steady state responses to hypoxia and hypercapnia were not diminished after 9-ANC but DIDS lowered the responses. Responses to NaCN effects were all diminished but those to nicotine were not affected. The results suggest that the functions of anion channels and HCO3-/Cl- exchangers are important for the resting dischargers and for the fast responses to hypoxia and hypercapnia.
4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
K+-current modulated by PO2 in type I cells in rat carotid body is not a chemosensor.
According to the membrane channel hypothesis of carotid body O2 chemoreception, hypoxia suppresses K+ currents leading to cell depolarization, [Ca2+]i rise, neurosecretion, increased neural discharge from the carotid body. We show here that tetraethylammonium (TEA) plus 4-aminopyridine (4-AP) which suppressed the Ca2+ sensitive and other K+ currents in rat carotid body type I cells, with and without low [Ca2+]o plus high [Mg2+]o, did not essentially influence low PO2 effects on [Ca2+]i and chemosensory discharge. Thus, hypoxia may suppress the K+ currents in glomus cells but K+ current suppression of itself does not lead to chemosensory excitation. Therefore, the hypothesis that K+-O2 current is linked to events in chemoreception is not substantiated. K+-O2 current is an epiphemenon which is not directly linked with O2 chemoreception.
4-Aminopyridine↗
Inhibition of dopamine release with simultaneous chemosensory excitation by hypercapnia with and without [Ca2+]0 in the cat carotid body.
The hypothesis that dopamine (DA) overflow corresponds to carotid sinus nerve (CSN) discharge during hypercapnia and is dependent on [Ca2+]0 was tested. We simultaneously measured the time course of DA overflow and CSN discharge of the cat carotid body, perfused/superfused in vitro at 37 degrees C at decreasing [Ca2+]0, during transition from normocapnia (PCO2 approximately 30-35 Torr) to hypercapnia (PCO2 approximately 60-65 Torr). In the presence of normal [Ca2+]0, hypercapnia instantaneously increased nerve discharge to peak levels followed by a decrease to steady states which were above the basal rate of activity. CSN discharge rate did not differ at decreasing [Ca2+]0 between 2.2 and 1.0 mM, and it began to decline at 0.1 mM [Ca2+]0, culminating to zero level in most cases, at zero [Ca2+]0. DA overflow increased slightly during hypercapnic peak CSN activity. Thereafter it declined to steady state levels below those of normocapnic conditions. Decreases in steady state DA levels were significantly less at 0 mM [Ca2+]0 compared to the higher calcium concentrations (0.1, 1.0 and 2.2 mM). Overall, steady state CSN activity and DA overflow were inversely related. Thus, DA release cannot have excitatory implications for carotid chemoreceptors during hypercapnia in the cat.
Animals↗
Suppression of glomus cell K+ conductance by 4-aminopyridine is not related to [Ca2+]i, dopamine release and chemosensory discharge from carotid body.
The hypothesis that suppression of O2-sensitive K+ current is the initial event in hypoxic chemotransduction in the carotid body glomus cells was tested by using 4-aminopyridine (4-AP), a known suppressant of K+ current, on intracellular [Ca2+]i, dopamine secretion and chemosensory discharge in cat carotid body (CB). In vitro experiments were performed with superfused-perfused cat CBs, measuring chemosensory discharge, monitoring dopamine release by microsensors without and with 4-AP (0.2, 1.0 and 2.0 mM in CO2-HCO3- buffer) and recording [Ca2+]i by ratio fluorometry in isolated cat and rat glomus cells. 4-AP decreased the chemosensory activities in normoxia but remained the same in hypoxia and in flow interruption. It decreased the tissue dopamine release in normoxia, and showed an additional inhibition with hypoxia. Also, 4-AP did not evoke any rise in [Ca2+]i in glomus cells either during normoxia and hypoxia, although hypoxia stimulated it. Thus, the lack of stimulatory effect on chemosensory discharge, inhibition of dopamine release and unaltered [Ca2+]i by 4-AP are not consistent with the implied meaning of the suppressant effect on K+ current of glomus cells.
4-Aminopyridine↗
Tissue oxygen sensing and the carotid body.
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Animals↗
Vascular and metabolic effects of nitric oxide synthase inhibition evaluated by tissue PO2 measurements in carotid body.
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Animals↗
Immunodetection of manganese superoxide dismutase in cultured human retroocular fibroblasts using sera directed against the thyrotropin receptor.
The identification of antigenic targets in the retroocular autoimmune response of Graves' ophthalmopathy is likely to increase our understanding of mechanisms underlying this disorder. While a number of putative autoantigens have been identified on the basis of molecular weight or cell of origin, a determination of the significance of these antigens is contingent upon an identification of the amino acid sequence. Our group has previously identified immunoreactive retroocular fibroblast (ROF) proteins recognized by thyrotropin receptor (hTSH-R) antisera (anti-p1), at molecular weights of 95, 71, 41, and 14-25 kDa. In the present study, proteins detected by anti-p1 and visualized by Ponceau staining were isolated and processed for microsequencing. Ponceau staining revealed dense bands at molecular weights of 14 and 23 kDa, and a weak band at 41 kDa. N-terminal sequencing was performed on the prominent band at approximately 23 kDa, showing it to be manganese superoxide dismutase (MnSOD), a mitochondrial enzyme responsible for protection against oxygen free radical-associated cellular damage. Sequence comparison of MnSOD to the hTSH-R peptide, p1, revealed a linear segment of amino acid homology. Preincubation of anti-p1 with p1 blocked immunodetection of the 23 kDa band corresponding to MnSOD, and immunoprecipitation of ROF protein using anti-pi yielded protein recognized by anti-MnSOD. Autoimmunity against human recombinant MnSOD was further assessed by ELISA. Patients with Graves' disease (n = 53) had significantly higher ELISA indices than normal control subjects (n = 29), while patients with Hashimoto's thyroiditis had intermediate values. These results document MnSOD autoantibodies in patients with Graves' disease and suggest that this may result from an immune cross-reactivity between MnSOD and the TSH-receptor.
Amino Acid Sequence↗
Dopamine, sensory discharge, and stimulus interaction with CO2 and O2 in cat carotid body.
It is hypothesized that carotid body chemosensory activity is coupled to neurosecretion. The purpose of this study was to examine whether there was a correspondence between carotid body tissue dopamine (DA) levels and neuronal discharge (ND) measured from the carotid sinus nerve of perfused cat carotid bodies and to characterize interaction between CO2 and O2 in these responses. ND and tissue DA were measured after changing from normoxic, normocapnic control bicarbonate buffer (PO2 >120 Torr, PCO2 25-30 Torr, pH approximately 7.4) to normoxic hypercapnia (PCO2 55-57 Torr, pH 7.1-7.2) or to hypoxic solutions (PO2 30-35 Torr) with normocapnia (PCO2 25-30 Torr, pH approximately 7.4) or hypocapnia (PCO2 10-15 Torr, pH 7.6-7.8). Similar temporal changes for ND and tissue DA were found for all of the stimuli, although there was a much different proportional relationship for normoxic hypercapnia. Both ND and DA increased above baseline values during flow interruption and normocapnic hypoxia, and both decreased below baseline values during hypoxic hypocapnia. In contrast, normoxic hypercapnia caused an initial increase in ND, from a baseline of 175 +/- 12 (SE) to a peak of 593 +/- 20 impulses/s within 4.6 +/- 0.9 s, followed by adaptation, whereas ND declined to 423 +/- 20 impulses/s after 1 min. Tissue DA initially increased from a baseline of 17.9 +/- 1.2 microM to a peak of 23.2 +/- 1.2 microM within 3.0 +/- 0.7 s, then declined to 2.6 +/- 1.0 microM. The substantial decrease in tissue DA during normoxic hypercapnia was not consistent with the parallel changes in DA with ND that were observed for hypoxic stimuli.
Animals↗
Regulating the ventilatory pump: a splendid control system prone to fail during sleep.
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Altitude↗
Dopamine increases in cat carotid body during excitation by carbon monoxide: implications for a chromophore theory of chemoreception.
Studies of dopamine (DA) release were conducted with 10 perfused/superfused cat carotid bodies using shallow recessed Nafion polymer-coated microsensors (tips approximately 5 microns). Simultaneous measurements of tissue DA and neuronal discharge (ND) from the sinus nerve were made after switching from normoxic, normocapnic control perfusate (20% O2, 5% CO2, balance N2) to a normoxic, normocapnic perfusate equilibrated with a high tension (> 550 Torr) of carbon monoxide (CO). When high PCO perfusate was delivered in the dark, ND increased from a baseline of 89 +/- 24 (SE) impulses/s, to a peak excitation of 374 +/- 44 impulses/s within 15-30 s. Excitation then diminished to a plateau of 281 +/- 36 impulses/s within 1-2 min. Both peak and plateau ND were significantly above baseline (P < 0.05). Average tissue DA values increased above basal levels by +7.2 +/- 1.0 and +5.6 +/- 0.6 microns, respectively, during the peak and plateau ND phases (P < 0.05). Bright light restored the chemosensory activity to baseline, but had no effect on DA. Both chemosensory excitation and tissue DA responses to high CO in the dark were diminished in 3 carotid bodies perfused with Ca(2+)-free solutions. Responses were reduced even further with Ca2+ chelator (EGTA) in the perfusate. The results suggest that the effect of high PCO on DA release and chemosensory excitation are dependent on Ca2+ in the media, but the two events are not coupled.
Action Potentials↗
Acid-sensing by carotid body is inhibited by blockers of voltage-sensitive Ca2+ channels.
The membrane potential hypothesis that the responses to hypercapnia of carotid chemosensory activity is mediated by voltage-gated Ca2+ channels was investigated by measuring directly the chemosensory output from rat and cat carotid bodies, perfused and superfused in vitro. We found that the inorganic and organic blockers of voltage-gated Ca2+ channels suppressed the hypercapnic responses, thereby supporting the membrane potential hypothesis.
Acids↗