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A Mokashi

Publications and source records attributed to A Mokashi.

At least 37 records · Page 2Linked to original sources
PubMed2000

P(O(2))-P(CO(2)) stimulus interaction in [Ca(2+)](i) and CSN activity in the adult rat carotid body.

Since glomus cell intracellular calcium ([Ca(2+)](i)) plays a key role in generating carotid sinus nerve (CSN) discharge, we hypothesized that glomus cell [Ca(2+)](i) would correspond to CSN discharge rates during P(O(2))-P(CO(2)) stimulus interaction in adult rat carotid body (CB). Accordingly, we measured steady state P(O(2))-P(CO(2)) interaction in CSN discharge rates during hypocapnia (P(CO(2))=8-10 Torr), normocapnia (P(CO(2))=33-35 Torr) and hypercapnia (P(CO(2))=68-70 Torr) in normoxia (P(O(2)) approximately 130 Torr) and hypoxia (P(O(2)) approximately 36 Torr). The results showed P(O(2))-P(CO(2)) stimulus interaction in CSN responses. [Ca(2+)](i) levels were measured in isolated type I cells (2-3 cells/field), using Ca(2+) sensitive fluoroprobe indo-1AM. The [Ca(2+)](i) responses increased with increasing P(CO(2)) in normoxia. In hypoxia, [Ca(2+)](i) did not increase during hypocapnia but increased during normocapnia, showing P(O(2))-P(CO(2)) interaction. However, CSN response during hypoxia was far greater than that for [Ca(2+)](i) response, particularly during hypocapnic hypoxia. Thus, the [Ca(2+)](i) interaction cannot account for the whole CSN interaction. The origin of this CSN P(O(2)-)P(CO(2)) interaction must have occurred in part beyond cellular [Ca(2+)](i) interaction. Interactions at both sites (glomus cell membrane and sinus nerve endings) are reminiscent of reversible O(2)-heme protein reaction with a Bohr effect.

Animals↗
PubMed1999

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↗
PubMed1998

The soluble granulocyte-macrophage colony-stimulating factor receptor's carboxyl-terminal domain mediates retention of the soluble receptor on the cell surface through interaction with the granulocyte-macrophage colony-stimulating factor receptor beta-subunit.

The hematopoietic cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF) mediates its activity through binding to cell-surface receptors. The high-affinity GM-CSF receptor (GMR) consists of two transmembrane-anchored subunits: a ligand-specific, low-affinity subunit (GMRalpha); and a signal-transducing beta-subunit (GMRbeta). The human GMRalpha subunit also exists in a soluble isoform (SOLalpha) which antagonizes GM-CSF activity in vitro. Previous studies by us have shown that coexpression of SOLalpha and a mutated GMRbeta in BHK cells results in retention of SOLalpha on the cell surface and the formation of an intermediate affinity binding complex (Kd approximately 300 pM). This paper investigates the mechanism of the retention of SOLalpha on the cell surface. The data demonstrate that SOLalpha is anchored by a direct, ligand-independent interaction with GMRbeta which also occurs when SOLalpha is coexpressed with wild-type GMRbeta. However, SOLalpha and wild-type GMRbeta form a complex which binds GM-CSF with high affinity (Kd = 39 pM), indistinguishable from the binding characteristics of the TMalpha/GMRbeta complex. The experiments further reveal that the interaction between SOLalpha and GMRbeta is abrogated by removal of the unique 16 amino acid carboxyl-terminal domain of SOLalpha. Specific mutation of cysteine 323 in this carboxyl-domain to alanine also eliminates the cell-surface retention of SOLalpha identifying this residue as being necessary for the formation of the SOLalpha/GMRbeta complex.

Amino Acid Sequence↗
PubMed1998

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↗
PubMed1998

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↗
PubMed1998

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↗
PubMed1998

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↗
PubMed1998

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↗
PubMed1998

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↗
PubMed1998

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↗
PubMed1997

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↗
PubMed1997

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↗
PubMed1997

Effect of CO on VO2 of carotid body and chemoreception with and without Ca2+.

This study was done using high PCO (> 500 Torr at PO2 of 120 Torr) in the carotid body perfusate in vitro, and recording simultaneously the activity of the whole carotid sinus nerve (CSN) and VO2 of the carotid body. In the cascade of excitation of CSN by high PCO in the dark [light eliminated the excitation; S. Lahiri, News Physiol. Sci. 9 (1992) 161-165], Ca2+ effects occur at the level of neurosecretion after the level of oxygen consumption, according to the following scheme: CO-hypoxia-->VO2 decrease-->K+ conductance decrease-->cell depolarization-->cytosolic Ca2+ rise-->neurosecretion-->neural discharge. Thus, a part of the hypothesis was that [Ca2+] decrease, being a downstream event, may not affect VO2 of the carotid body. Also, to determine to what extent the intracellular calcium stores contribute to cystolic [Ca2+] and chemosensory discharge with high PCO, we tested the effect of interruption of perfusate flow with medium nominally free of [Ca2+] on CSN excitation and VO2 of the carotid body with and without high PCO. High PCO in the dark decreased carotid body VO2, independent of [Ca2+]o. CSN excitation was always enhanced by high PCO, and its sensitivity to perfusate flow interruption. Also, nominally Ca(2+)-free solution increased the latency and decreased the rate of rise and peak activity of CSN during interruption of perfusate flow, but CO augmented the responses. This reversal effect by CO suggests that Ca2+ is released from intracellular stores, because CO has no other way to excite the chemoreceptors than by acting on the intracellular stores.

Animals↗
PubMed1997

CO interact with intracellular [H+] with and without CO2-HCO3- in the cat carotid chemosensory discharge.

To test the hypothesis whether CO2-HCO3- buffer is essential for the expression of chemoreception and to distinguish between pHi and pHo interaction with pCO in the carotid chemosensory response, we superfused-perfused in vitro cat carotid bodies using HEPES-Tyrode's solution with and without CO2-HCO3-, and compared the responses at the same pHo in the absence and presence of light. In the absence of light, pCO (> 138 Torr) stimulated the carotid body chemoreceptors in CO2-HCO3- buffer at pHo of 7.40, whereas pCO (69-550 Torr) did not stimulate the neural discharge in HEPES buffer at the pHo of 7.4-7.1 but did so below pHo 7.1. In the presence of light, all the responses were diminished proportionately.

Animals↗
PubMed1997

Potential role of H2O2 in chemoreception in the cat carotid body.

The hypothesis that H2O2 plays a critical role in hypoxic chemoreception in the cat carotid body (CB) was tested using a perfused-superfused preparation in vitro, measuring chemosensory discharge and CB tissue PO2 (PtiO2). According to the hypothesis NADPH mediated, PO2 dependent increase in H2O2 production would hyperpolarize the glomus cell, decreasing the chemosensory discharge. Thus, lactate and aminotriazole which would increase H2O2 concentration, would decrease the chemosensory discharge during hypoxia. However, 2.5-5.0 mM lactate and 25 mM aminotriazole did not diminish the hypoxic response. But, 2.5 mM lactate decreased the chemosensory discharge during normoxia which can be explained by an increase of CB PtiO2. Diethyldithiocarbamic acid (5 mM), which blocks the conversion of superoxide to H2O2, also diminished the chemosensory discharge, presumably due to an increased CB PtiO2. Menadione (increasing H2O2) and t-butyl hydroperoxide irreversibly decreased the chemosensory discharge, and the data are not useful. H2O2 increased the PO2 of the perfusate, and therefore could not be tested against PO2. Thus, perturbation of endogenous or exogenous H2O2 did not provide any evidence for its critical role in O2 chemoreception.

Amitrole↗
PubMed1997

Cat carotid body chemosensory discharge (in vitro) is insensitive to charybdotoxin.

Charybdotoxin (ChTX), a venom protein, suppresses Ca2+-activated K+ (K+(Ca)) currents in the glomus cell of neonatal rat carotid body. If it works similarly for cat carotid body chemoreceptors, charybdotoxin is expected to stimulate the chemosensory discharge during normoxia, and particularly hypoxia and hypercapnia. We studied the effects of charybdotoxin (20-40 nM) in vitro (perfused/superfused) on the cat carotid chemosensory discharge, and simultaneously tissue PO2 (PtiO2), as a measure of positive control. ChTX (20 nM) only increased PtiO2 and decreased carotid chemosensory discharge during hypoxia, indicating vasodilation. We conclude that K+(Ca) channels do not appear to play a significant role in chemotransduction in the cat carotid body.

Animals↗