Competitive Inhibition of NMDA Receptor–Mediated Currents by Extracellular Calcium Chelators

2000 ◽  
Vol 84 (2) ◽  
pp. 693-697 ◽  
Author(s):  
Nansheng Chen ◽  
Timothy H. Murphy ◽  
Lynn A. Raymond
Keyword(s):  
Nmda Receptor ◽  
Nmda Receptors ◽  
Dose Response ◽  
Response Curve ◽  
Competitive Inhibition ◽  
Response Shift ◽  
Dose Response Curve ◽  
Hek 293 ◽  
Electrophysiological Recordings ◽  
The Right

Calcium chelators have been widely used in electrophysiological recordings of N-methyl-d-aspartate (NMDA) receptor–mediated currents, as well as in studies of excitotoxicity. Intracellularly applied calcium chelators are known to inhibit, at least in part, such calcium-dependent processes as calmodulin-dependent inactivation, calcineurin-dependent desensitization, and rundown of NMDA receptors. On the other hand, the functional consequences and potential nonspecific effects of extracellularly applied chelators have not been extensively investigated. In whole-cell patch-clamp recordings from human embryonic kidney (HEK) 293 cells transiently transfected with recombinant NMDA receptors, we found that addition of calcium chelators such as EGTA shifted the glutamate dose-response curve to the right, from an EC50 for NR1A/NR2A of 8 μM in 1.8 mM Ca2+ to ∼24 μM in a solution containing nominal 0 Ca2+/5 mM EGTA and further to ∼80 μM in 20 mM EGTA. A similar shift in glutamate dose-response was observed for NR1A/NR2B currents. This dose-response shift was not due to a decrease in extracellular Ca2+ concentration because there was no change in the glutamate EC50 at Ca2+concentrations ranging from 10 mM to nominal 0/200 μM EGTA. Moreover, addition of 5 mM EGTA fully chelated with 6.8 mM Ca2+ did not produce any shift in the glutamate dose-response curve. We propose that calcium chelators, containing four free carboxyl moieties, competitively inhibit glutamate binding to NMDA receptors.

Copper inhibits pressor responses to noradrenaline but not potassium. Interactions with prostaglandins E1, E2, and I2 and penicillamine

1979 ◽  
Vol 57 (1) ◽  
pp. 35-40 ◽  
Author(s):  
S. C. Cunnane ◽  
H. Zinner ◽  
D. F. Horrobin ◽  
M. S. Manku ◽  
R. O. Morgan ◽  
...  
Keyword(s):  
Dose Response ◽  
Response Curve ◽  
Wilson’S Disease ◽  
Wilson's Disease ◽  
Biological Action ◽  
Dose Response Curve ◽  
Low Concentrations ◽  
Pressor Responses ◽  
The Right ◽  
Copper Effect

Low concentrations of copper inhibited responses to norepinephrine and angiotensin (IC50 3 × 10−6 M) but not to potassium in rat mesenteric vascular preparations perfused either with buffer or indomethacin and prostaglandin (PGE2). The dose–response curve was not shifted by indomethacin, imidazole, or PGE2 but was moved to the right by 2.8 × 10−11 M PGE1 and to the left by 2.8 × 10−7 M PGE1. These effects of copper are similar to the effects of PGI2 in the preparation. Copper moved the PGI2 dose–response curve against noradrenaline in parallel to the left, suggesting that the two were interacting at some point. Penicillamine, which may stimulate PGE1 synthesis, had PGE1-like interactions with the copper effect, suggesting that its value in Wilson's disease may be partly due to antagonism of the biological action of copper as well as to its copper-chelating properties.

Alteration of islet neurotransmitter sensitivity following ventromedial hypothalamic lesion

1983 ◽  
Vol 244 (5) ◽  
pp. R635-R640 ◽  
Author(s):  
L. A. Campfield ◽  
F. J. Smith
Keyword(s):  
Insulin Secretion ◽  
Beta Cell ◽  
Dose Response ◽  
Response Curve ◽  
Pancreatic Beta Cell ◽  
Dose Response Curve ◽  
Norepinephrine Dose ◽  
Increased Sensitivity ◽  
The Right ◽  
Glucose Responsiveness

Recent studies suggest that alterations in autonomic neural activity may mediate the obese state observed following ventromedial hypothalamic (VMH) lesion. To assess the role of these alterations in the increased glucose responsiveness of the beta-cell observed in this state, we have determined the sensitivity of insulin secretion to norepinephrine or/and acetylcholine in statically incubated pancreatic islets from rats 30-40 days after VMH lesion. In islets from VMH-lesioned rats compared with islets from sham-operated and intact rats, the acetylcholine dose-response curve was shifted down and to the right, indicating a decreased sensitivity, whereas the norepinephrine dose-response curve was translated to the left, indicating an increased sensitivity. The interaction profile, which summarizes combined neurotransmitter exposure on insulin secretion, was shifted in the direction of net inhibition. Thus it was concluded that, following VMH lesion, autonomic neurotransmitter sensitivity of the pancreatic beta-cell was altered. It is suggested that these alterations play a role in the adaptation of the beta-cell to the experimentally induced obese state.

Leukotriene receptor on U-937 cells: discriminatory responses to leukotrienes C4 and D4

1991 ◽  
Vol 261 (2) ◽  
pp. L164-L171 ◽  
Author(s):  
L. A. Wetmore ◽  
N. P. Gerard ◽  
D. K. Herron ◽  
N. G. Bollinger ◽  
S. R. Baker ◽  
...  
Keyword(s):  
Cell Surface ◽  
Dose Response ◽  
Response Curve ◽  
Spatial Configuration ◽  
Dose Response Curve ◽  
Striking Difference ◽  
Cell Surface Receptors ◽  
Leukotriene D4 ◽  
Surface Receptors ◽  
The Right

Dimethyl sulfoxide (DMSO)-differentiated U-937 cells develop cell surface receptors for leukotrienes that, when stimulated, initiate a transient increase in intracellular calcium concentration [( Ca2+]i). We investigated the calcium transient that occurs after addition of leukotriene C4 (LTC4) to determine whether it occurs due to 1) the bioconversion of LTC4 to leukotriene D4 (LTD4), which then acts at the LTD4 receptor; 2) the direct action of LTC4 at the LTD4 receptor; or 3) the action of LTC4 at a receptor selective for LTC4. Bioconversion of [3H]LTC4 to [3H]LTD4 was inhibited by 98% when DMSO-differentiated U-937 cells were incubated with 10 mM AT-125 compared with control cells. The dose-response curve for LTC4, with [Ca2+]i as the index of response, was parallel to that for LTD4 but was significantly (P less than 0.0001) shifted 1.6 +/- 0.11 log units to the right. AT-125 did not change the response to LTD4 but the LTC4 dose-response curve was shifted on additional 1.7 logo units to the right. The antagonists SKF 104353 (1 microM) and LY 171883 (10 microM) shifted the dose-response curve for LTD4 3.0 +/- 0.23 and 2.5 +/- 0.23 log units, respectively, to the right and completely inhibited the change in [Ca2+]i due to LTC4 in the presence of 10 mM AT-125. Molecular modeling studies demonstrated a striking difference in the spatial configuration of LTC4 and LTD4, likely accounting for the ability of cell surface receptors to discriminate between the effects of these two molecules.(ABSTRACT TRUNCATED AT 250 WORDS)

Histamine Receptors in Normal Human Bronchi

1980 ◽  
Vol 58 (6) ◽  
pp. 537-544 ◽  
Author(s):  
Noemi M. Eiser ◽  
Jane Mills ◽  
K. D. McRae ◽  
P. D. Snashall ◽  
A. Guz
Keyword(s):  
Receptor Antagonist ◽  
Dose Response ◽  
Response Curve ◽  
Normal Subjects ◽  
Dose Response Curve ◽  
Significant Shift ◽  
H2 Receptor Antagonist ◽  
Anticholinergic Activity ◽  
H2 Receptor ◽  
The Right

1. Nine normal subjects inhaled increasing concentrations of histamine aerosol from an aerosol generator attached to a breath-actuated dosimeter. The responses were monitored by measuring specific airways-conductance in a body plethysmograph, and the results were expressed as cumulative log dose-response curves. On separate days, histamine challenges were repeated after intravenous injections of sodium chloride solution (placebo), or an H1-receptor antagonist chlorpheniramine, or an H2-receptor antagonist cimetidine, or H1- and H2-receptor antagonists together. The anticholinergic activity of chlorpheniramine was estimated by comparing the effect of chlorpheniramine and atropine on methacholine challenge. 2. In all subjects the response to histamine was reproducible. Analysis of the variance showed that placebo did not alter the histamine dose-response curve significantly. In contrast, chlorpheniramine produced a large shift in the histamine dose-response curve to the right and cimetidine produced a significant shift of this curve to the right only at the highest dose of histamine. A combination of cimetidine and chlorpheniramine produced a shift not significantly different from that seen with chlorpheniramine alone. Chlorpheniramine showed no significant anticholinergic activity in this study. 3. In the normal subjects histamine-induced bronchoconstriction appeared to be mediated predominantly by the H1-receptors. The H2-receptor contributed very little to this bronchoconstriction.

Postsynaptic potentiation and desensitization in frog neuromuscular junction

1988 ◽  
Vol 66 (5) ◽  
pp. 624-629 ◽  
Author(s):  
M. I. Glavinqvić
Keyword(s):  
Neuromuscular Junction ◽  
Dose Response ◽  
Response Curve ◽  
Dose Response Curve ◽  
Maximal Response ◽  
Frog Neuromuscular Junction ◽  
Receptor Complexes ◽  
Fractional Increase ◽  
The Right ◽  
Postsynaptic Potentiation

The fractional increase in ACh responses that occurs at the beginning of each train of iontophoretically applied ACh pulses has been examined at the frog neuromuscular junction at room temperature, in the presence of active cholinesterase, during desensitization produced by a rapid sequence (every 20 s) of short (5 Hz, 5 s) iontophoretic trains of ACh. The fractional increase in ACh responses, which is used as an indicator of postsynaptic potentiation, becomes progressively greater with ACh application, often markedly (>100%), although ACh responses are greatly reduced (as much as 90%) owing to desensitization. Clearly postsynaptic potentiation can exist concomitantly with desensitization. In addition, the dose–response curve is shifted to the right and its maximal response is diminished. The shift in the dose–response curve to the right, which can explain greater postsynaptic potentiation, is unlikely to be caused by accumulation of "monoligand-bound ACh receptor complexes," since experiments were done with active cholinesterase. The shift probably results from a greater number of desensitized receptors which, because of their large affinity for ACh molecules, serve as "high affinity traps." A small decrease of the maximal dose–response suggests only a small fractional decrease in the number of activable receptors, whereas a large shift to the right indicates a large fractional increase in the number of desensitized receptors. It appears that prior to ACh application only a small fraction of all receptors are desensitized. Alternatively, the shift to the right occurs because the cooperative action of ACh on receptors increases during desensitization.

Desensitisation in Human and Rabbit Blood Platelets

1982 ◽  
Vol 47 (03) ◽  
pp. 278-284 ◽  
Author(s):  
T J Hallam ◽  
P A Ruggles ◽  
M C Scrutton ◽  
R B Wallis
Keyword(s):  
Dose Response ◽  
Response Curve ◽  
Blood Platelets ◽  
Human Platelets ◽  
Dose Response Curve ◽  
Maximal Response ◽  
Significant Shift ◽  
Type I ◽  
Rabbit Blood ◽  
The Right

Summary1. Exposure of human and rabbit blood platelets to all full agonists tested induces agonist-specific (or homologous) desensitisation except in the case of adrenaline and collagen in human platelets.2. Desensitisation to vasopressin and 5-hydroxytryptamine (5HT) develops rapidly and results from suppression of maximal responsiveness without significant shift in the dose/response curve (Type I). In rabbit platelets, maintenance of desensitisation to 5HT is correlated with the extracellular 5HT concentration. Responsiveness to other agonists is either unaffected, or is enhanced due to a shift in the dose/response curve to the left without change in maximal responsiveness.3. Homologous desensitisation to ADP, U-46619 and thrombin develops more slowly, is correlated with disaggregation and is associated with a shift in the dose/response curve to the right without suppression of maximal responsiveness (Type II). Responsiveness to most other agonists is either unaffected, or is enhanced due to a shift in the dose/response curve to the left without a change in maximal responsiveness. However, exposure to thrombin suppresses the maximal response to vasopressin without a shift in the dose/response curve, and exposure to U-46619 causes a shift in the dose/response curve for collagen to the right.4. In human platelets prolonged exposure to 5HT causes agonist non-specific (or heterologous) desensitisation in which responsiveness to all agonists except adrenaline is suppressed as a result of shifts in the dose/response curves to the right.5. We propose that Types I and II homologous desensitisation result respectively from prolonged receptor occupancy and from either activation of degradative mechanisms for the agonist or processing of the receptor to a lower affinity state.

Role of Endothelial K + Channels in NO-Dependent Vasorelaxant Responses to Acetylcholine in Rat Aorta.

Hypertension ◽  
2000 ◽  
Vol 36 (suppl_1) ◽  
pp. 698-698
Author(s):  
John Quilley ◽  
Yue Qiu
Keyword(s):  
Dose Response ◽  
Response Curve ◽  
Rat Aorta ◽  
Dose Response Curve ◽  
Response Curves ◽  
K Channels ◽  
Voltage Dependent ◽  
The Right ◽  
Stimulation Of

P30 Endothelium-dependent vasorelaxant responses to acetylcholine (Ach) in rat aorta are mediated solely by NO. Rings precontracted with U46619 were used to investigate the role of endothelial K + channels. Thus, any effect of K + channel inhibitors on Ach responses in the absence of an effect on those to nitroprusside (NP) can be attributed to interference with Ach-induced stimulation of NO. Vasorelaxant responses to Ach (log EC 50 -7.29M) were abolished by removal of the endothelium or inhibition of NO synthesis with nitroarginine (100μM) which potentiated responses to NP (log EC 50 -9.41M vs -8.47M for control). In the presence of TEA (10mM) to inhibit K + channels, the dose-response curve for Ach, but not NP, was shifted to the right (log EC 50 -6.06). Elevation of extracellular K + (25mM KCl)also shifted the dose-response curve for Ach to the right. Inhibitors of specific types of K + channels: BaCl 2 (30μM), apamin (100nM), glibenclamide (10μM), charybdotoxin (50nM) and iberiotoxin (100nM) were without effect on dose-response curves to either Ach or NP. However, the combination of apamin (100nM) and charybdotoxin (50nM) but not apamin plus iberiotoxin, reduced relaxant responses to Ach (log EC 50 -6.95M) without affecting those to NP.These results confirm that Ach-induced relaxation of rat aorta is mediated entirely by endothelium-derived NO, the release of which apparently involves hyperpolarization of the endothelium. This effect is dependent on activation of a K + channel that is blocked by a combination of apamin/charybdotoxin but neither agent alone, possibly indicating characteristics of both Ca 2+ - activated and voltage-dependent K + channels.

The Effect of Vagotomy on the Lower Part of the Acid Dose-Response Curve to Pentagastrin in Man

1972 ◽  
Vol 43 (2) ◽  
pp. 193-200 ◽  
Author(s):  
J. B. Elder ◽  
G. Gillespie ◽  
E. H. G. Campbell ◽  
I. E. Gillespie ◽  
G. P. Crean ◽  
...  
Keyword(s):  
Duodenal Ulcer ◽  
Dose Response ◽  
Response Curve ◽  
Response Pattern ◽  
Positive Response ◽  
Dose Response Curve ◽  
Threshold Dose ◽  
Truncal Vagotomy ◽  
Small Doses ◽  
The Right

1. The acid secretory responses to insulin of forty-seven duodenal ulcer patients after truncal vagotomy and drainage were classified according to the criteria of Hollander (1946) into positive or negative. 2. The acid response to ranges of small doses of pentagastrin was studied in these two groups. In the group with a positive acid response after insulin the dose-response pattern to pentagastrin was very similar to that in preoperative patients. 3. In those who failed to satisfy criteria for a positive response after insulin the dose-response curve to pentagastrin appeared to shift to the right. It had a lower level and a smaller slope. Truncal vagotomy appeared to cause an eightfold increase in the threshold dose found in preoperative patients. 4. Supersensitivity of the stomach to small doses of pentagastrin after vagotomy was not apparent in the present study.

Glucocorticoids inhibit acetylcholine-induced current in chromaffin cells

1989 ◽  
Vol 257 (5) ◽  
pp. C906-C912 ◽  
Author(s):  
M. Inoue ◽  
H. Kuriyama
Keyword(s):  
Dose Response ◽  
Sodium Salt ◽  
Response Curve ◽  
Membrane Conductance ◽  
Dose Response Curve ◽  
Hill Coefficient ◽  
Outer Cell ◽  
Membrane Excitability ◽  
Patch Clamp Technique ◽  
The Right

The effects of dexamethasone, a synthetic glucocorticoid, on membrane excitability and on the acetylcholine (ACh)-induced inward current (IACh) were studied in dispersed guinea pig adrenal medullary cells by using the whole cell version of the patch-clamp technique. Bath application of 10 microM dexamethasone had no effect on the resting membrane conductance or voltage-gated Na+, Ca2+, or K+ channels, whereas it reversibly inhibited the IACh at a holding potential of -70 mV. Intracellular application of dexamethasone through the patch electrode did not modify the IACh. Application of 10 microM dexamethasone neither shifted the dose-response curve of the peak IACh to the right [dissociation constant (Kd) = 50 microM] nor affected its Hill coefficient (1.2) but inhibited the current amplitudes by approximately 41% in the cells sufficiently pretreated with dexamethasone. Furthermore, fractional inhibition of the IACh at the end of approximately 50-s application was the same for any concentration of ACh (3-100 microM). The dose-response curve of the inhibition by dexamethasone showed a good fit to the theoretical line assuming an inhibition constant (Ki) of 10 microM and a Hill coefficient of 1. Hydrocortisone 21-hemisuccinate sodium salt (25 microM) and prednisolone 21-hemisuccinate sodium salt (25 microM) inhibited the IACh to a lesser extent than 25 microM dexamethasone. These results suggest that dexamethasone binds to the specific site on the outer cell membrane, probably on the ACh receptor-coupled channel, and inhibits the IACh in a noncompetitive manner, thus controlling the immediate catecholamine release from the adrenal medulla.

Histamine dose-response curves in guinea pigs

1985 ◽  
Vol 58 (2) ◽  
pp. 625-634 ◽  
Author(s):  
W. C. Hulbert ◽  
T. McLean ◽  
B. Wiggs ◽  
P. D. Pare ◽  
J. C. Hogg
Keyword(s):  
Dose Response ◽  
Guinea Pigs ◽  
Response Curve ◽  
Dynamic Compliance ◽  
Dose Response Curve ◽  
Base Line ◽  
Response Curves ◽  
Mechanically Ventilated ◽  
Dose Response Curves ◽  
The Right

Histamine dose-response curves were performed on anesthetized tracheostomized guinea pigs that were paralyzed and mechanically ventilated at a constant tidal volume and breathing frequency. The dose was calculated by generating an aerosol of known concentration and measuring the volume delivered to the lung. Increasing the dose was accomplished by increasing the number of breaths of aerosol delivered. The response to each dose was determined by measuring the change in airway resistance (RL) and dynamic compliance (Cdyn) using the method of Von Neergaard and Wirz (Z. Klin. Med. 105: 51–82, 1927). With increasing doses of histamine, RL increased and reached a plateau at approximately five times the base-line value and Cdyn fell to approximately 20% of its initial value. The variability in the base-line and maximum response as well as the calculated sensitivity and reactivity was less than that previously reported. Propranolol pretreatment increased resting RL and shifted the dose-response curve for RL to the left of the controls, increasing reactivity but not sensitivity. Atropine shifted the dose-response curve to the right of the control, decreasing sensitivity but without changing reactivity. The data for Cdyn showed that atropine pretreatment caused a higher resting value and propranolol pretreatment a lower value at the highest histamine dose but no differences in either sensitivity or reactivity.

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