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1.
Calcium (Ca 2+) entry from the extra-cellular space into the cytoplasm through voltage-dependent Ca 2+ channels, specifically dipyridamole (DHP) sensitive ones (L-type), control a variety of biological processes, including excitation-contraction coupling in vascular and GI muscle cells. It has also been proposed that these channels may control esophageal contractility. However, DHP-sensitive Ca 2+ channels in esophagus have not been well characterized biochemically. Thus, it is not known if these channels are similar in number or affinity to those in vascular or neural tissues — organs for which clinical use of calcium channel blockers has been successful. Thus, the purpose of this study was to identify and characterize DHP-sensitive calcium channels in esophagus and compare them to vascular, neural, and other GI tissues. Methods — We carried out in vitro receptor binding assays on lower esophageal muscle homogenates, gastric and intestinal and colonic homogenates, and aortic muscle homogenates from ca; and on brain homogenates from rat. We used a radio-labeled dihydropyridine derivative [ 3H]nitrendipine, to label these sites and co-administration of unlabeled nimodipine to define specific binding. Results — As expected, ligand binding to L-type Ca 2+ channels in aortic vascular smooth muscle and brain was readily detectable: brain, Bmax = 252 fmol/mg protein, Kd = 0.88 nM; aorta, Bmax = 326 fmol/mg protein, Kd = 0.84 nM. For esophagus (Bmax = 97; Kd = 0.73) and for other GI tissues, using the same assay conditions, we detected a smaller signal, suggesting that L-type Ca 2+ channels are present in lower quantities. Conclusion — L-type Ca 2+ channel are present in esophagus and in other GI muscles, their affinity is similar, but their density is relatively sparse. These findings are consistent with the relatively limited success that has been experienced clinically in the use of calcium channel blockers for treatment of esophageal dysmotility. 相似文献
2.
The effect ot Cu 2+ and Ca 2+ ions, on the ultraviolet differential (UVD) spectra of single-stranded poly I was studied and the coordination (Δε b) and conformation (Δε c) conponents of the spectra calculated The comparison of Δε b and the UVD spectrum of protonated IMP leads to the conclusion that N(7) ot inosine-5'-monophosphate (IMP) is a coordinating site tor Ca 2+ and Cu 2+ ions on the polymer bases. The binding ot Ca 2+ and Cu 2+ ions causes differently directed displacements of the four absorption bands of poly I, which are observed in the wavenumber range (50-34) × 10 3 cm −1 The calculation of concentration dependencies tor the association constants ( K“) ot Ca 2+ and Cu 2+ ions binding to poly I bases shows that the binding is cooperative The K“ values for the poly I + Ca 2+ complex are two orders of magnitude lower than those for the poly 1 + Cu 2+ complex At low ion concentrations, binding to the poly I phosphates predominates and increases the degree of the polynucleotide helicity. At higher concentrations the spectra are mainly affected by the ion binding to bases, which results in melting of the helical parts of poly I At Ca 2+ concentrations exceeding 10 −3 M light-scattering aggregates are formed. The degree of monomer order in them is close to that observed in multistranded helices of poly I 相似文献
3.
1. 1.|The influence of temperature changes on Ca2+-binding to brain ganglioside mixtures of different polarity, to single gangliosides (GM1, GD1a, GT1b) and to their deceramide was investigated potentiometrically by means of ion-selective electrodes. 2. 2.|Following cooling (3.5°C/min.) from 37 to 13°C the Ca2+-binding to gangliosides, except GM1, was increased (7–30%). 3. 3.|Subsequent rewarming from 13 to 37°C resulted in up to 100% release of previously-bound Ca2+. 4. 4.|When comparing the maximal absolute binding difference of Ca2+ to gangliosides during temperature changes a decrease of these differences could be stated which corresponds to an increase in the polarity of the gangliosides. 5. 5.|From these experiments it is concluded that a higher polarity of neuronal gangliosides is responsible for a lower thermal sensitivity of Ca2+-binding to these compounds. This may be involved in the process of thermal adaptation of ectothermic vertebrates.
Author Keywords: Ganglioside—Ca2+ complex; temperature; potentiometry; Gallus domesticus; Salmo gairdneri; brain 相似文献
4.
Using a new fluorescence imaging technique, LAMP, we recently reported that Ca 2+ influx through store operated Ca 2+ channels (SOCs) strongly inhibits cell coupling in primary human fibroblasts (HF) expressing Cx43. To understand the mechanism of inhibition, we studied the involvement of cytosolic pH (pH i) and Ca 2+([Ca 2+] i) in the process by using fluorescence imaging and ion clamping techniques. During the capacitative Ca 2+ influx, there was a modest decline of pH i measured by BCECF. Decreasing pH i below neutral using thioacetate had little effect by itself on cell coupling, and concomitant pH i drop with thioacetate and bulk [Ca 2+i rise with ionomycin was much less effective in inhibiting cell coupling than Ca 2+ influx. Moreover, clamping pH i with a weak acid and a weak base during Ca 2+ influx largely suppressed bulk pH i drop, yet the inhibition of cell coupling was not affected. In contrast, buffering [Ca 2+i with BAPTA, but not EGTA, efficiently prevented cell uncoupling by Ca 2+ influx. We concluded that local Ca 2+ elevation subjacent to the plasma membrane is the primary cause for closing Cx43 channels during capacitative Ca 2+ influx. To assess how Ca 2+ influx affects junctional coupling mediated by other types of connexins, we applied the LAMP assay to Hela cells expressing Cx26. Capacitative Ca 2+ influx also caused a strong reduction of cell coupling, suggesting that the inhibitory effect by Ca 2+ influx may be a more general phenomenon. 相似文献
5.
We examined the profile of two bombesin (BN) antagonists, (CH 3) 2CHCO-His-Trp-Ala-Val-
-Ala-His-Leu-NHCH 3] (ICI 216140) and [
-Phe 6,des-Met 14]BN(6–14)ethylamide (DPDM-BN EA), against neuromedin B-induced Ca 2+ mobilization in the small cell lung cancer (SCLC) line NCI-H345. Neuromedin B (NMB), a BN-like peptide sharing sequence homology with ranatensin, elicited a concentration-dependent Ca 2+ release (in part) from intracellular stores. Sequential addition of NMB attenuated Ca 2+ mobilization. Desensitization occurred between BN and NMB; depletion of intracellular Ca 2+ is a likely mechanism because thapsigargin stimulated Ca 2+ release after a maximally desensitizing dose of NMB. ICI 216140 and DPDM-BN EA competitively inhibited BN-induced Ca 2+ transients. In contrast, these compounds antagonized NMB-stimulated Ca 2+ transients in a noncompetitive manner. The pharmacological profiles obtained support receptor heterogeneity for BN-like peptides on this SCLC line, underscoring the need for thorough examination of dose-response relationships when investigating effects of BN analogues on intact cells. 相似文献
6.
Charybdotoxin, a short scorpion venom neurotoxin, which was thought to be specific for the blockade of Ca 2+-activated K + channels also blocks a class of voltage-sensitive K + channels that are known to be the target of other peptide neurotoxins from snake and bee venoms such as dendrotoxin and MCD peptide. Charybdotoxin also inhibits 125-dendrotoxin and 125I-MCD peptide binding to their receptors. All these effects are observed with an IC 50 of about 30 nM. 相似文献
7.
Troponin prepared from rabbit skeletal muscle in the presence of dithiothreitol (SH-troponin) was found to have a sulfhydryl content of about 4 moles/1 × 10 5 g in the presence of a Ca 2+-chelating agent. The addition of physiological concentrations of Ca 2+ reduced the reactive sulfhydryl content to 2.0–2.5 moles/1 × 10 5 g. These sulfhydryl groups are evidently not direct participants in the inhibition of actomyosin superprecipitation, since treatment with N-ethylmaleimide had no effect on the Ca 2+-sensitizing activity of SH-troponin. Troponin prepared in the absence of dithiothreitol (S-S-troponin) showed a significant reduction in Ca2+-sensitizing activity, relative to SH-troponin. The sulfhydryl groups of S-S-troponin, approx. 2 moles/1 × 105 g were not appreciably affected by Ca2+. It is postulated that the Ca2+-sensitive sulfhydryl groups exist at a site which is essential for the regulatory function of troponin and which undergoes a conformational change upon the binding of Ca2+. 相似文献
8.
A scale of selectivity for the binding of calcium and some heavy metal ions by citrus and sugar-beet pectins was set up by pH-measurements. The same order of selectivity was found for the two pectins, decreasing as follows: Cu 2+ Pb 2+ Zn 2+ > Cd 2+ Ni 2+ ≥ Ca 2+. Binding isotherms for Ca 2+, Cu 2+, Ni 2+, Pb 2+ and Zn 2+ ions have shown a greater binding level when the ionic strength decreased and when the pectin concentration increased in the presence of 0.1 M NaNO 3. By comparing binding isotherms, the same order of selectivity was found as by pH-studies. Scatchard plots and Hill index evaluation showed for all ions and all pectins anticooperative interactions in water. In the presence of 0.1 M NaNO 3, citrus pectins displayed cooperative interactions for all metal ions. In contrast, for sugar-beet pectins, cooperative interactions only occured with Cu 2+ and Pb 2+. With Ca 2+, Ni 2+ and Zn 2+ sugar-beet pectins displayed Scatchard plots which could not be distinguished from an anticooperative binding. This difference of behaviour could be related to the presence of acetyl groups decreasing the affinity of Me 2+ for sugar-beet pectins. 相似文献
9.
This study demonstrates that Ca 2+ regulates thrombosthenin ATPase activity, likening the control of platelet contraction to that of cardiac and skeletal muscle. Thrombosthenin, the platelet contractile protein, was isolated by repeated low ionic strength and isoelectric precipitation. Thrombosthenin superprecipitation and ATPase activity were measured in 10 −4 M CaCl 2 (high ionized Ca 2+) and 0.25 mM ethylene glycol bis-(β-aminoethyl ether)- N, N′-tetraacetic acid (EGTA) (low ionized Ca 2+). In both high and low Ca 2+, superprecipitation, measured as an increase in turbidity, ocurred shortly after addition of ATP. ATP hydrolysis by thrombosthenin, which proceeded linearly for several hours, was greater in high Ca 2+ (approx. 2.3 nmoles·mg −1·min −1) than in low Ca 2+ (approx. 1.8 nmoles·mg −1·min −1). This difference, when analyzed by the Student's t-test for paired samples was highly significant ( P < 0.001). Thrombosthenin ATPase activity was not significantly altered by azide, an inhibitor of mitochondrial ATPase, nor by ouabain, an inhibitor of (Na + + K +)-activated ATPase. The dependence of thrombosthenin activation on ionized Ca 2+, measured with the use of CaEGTA buffers, was studied. The Ca 2+-dependent portion of thrombosthenin ATPase was half maximal at 4.5·10 −7 M Ca 2+. This corresponds to an apparent binding constant of 2.2·10 6 M −1, a value that is comparable to that of skeletal and cardiac muscle. These data suggest that a Ca 2+ control mechanism similar to that of the troponin-tropomyosin complex of muscle exists in the platelet. 相似文献
10.
Calcium activation of oxygen evolution from French-press preparations of Phormidium luridum is largely reversible upon removal of added Ca 2+. Activation occurs via a first-order binding with a dissociation constant of 2.8 mM. An 8-fold increase in oxygen evolution rate observed upon Ca 2+ addition is accounted for by a 4-fold increase in the number of active photosynthetic units, and a doubling of turnover rate. While both Ca 2+ and Mg 2+ stimulate turnover, unit activation is Ca 2+ specific. Under optimal conditions, 30% of the units functioning in the intact cell can be recovered in the Ca 2+-activated preparation. The Ca2+ requirement of P. luridum preparations is not relieved by proton-carrying uncouplers, or by rate-saturating concentrations of the Hill acceptor, ferricyanide. Taken together with the reported stimulation by Ca2+ of oxygen evolution in the presence of DCMU (Piccioni, R.G. and Mauzerall, D.C. (1976) Biochim. Biophys. Acta 423, 605–609) these observations strongly suggest a site of Ca2+ action within Photosystem II. The pronounced specificity of the Ca2+ requirement appears in preparations of other cyanobacteria (Anabaena flos-aquae and Anacystis nidulans) but not in the eucaryote Chlorella vulgaris. While milder cell-disruption methods bring about some Ca2+ dependence in P. luridum, French-press treatment is required for maximal expression of Ca2+-specific effects. French-press breakage causes a release of endogenous Ca2+ from cells, supporting the view that added Ca2+ restores oxygen evolution by satisfying a physiological requirement for the cation. 相似文献
11.
Calmodulin binding to a membrane fraction enriched in synaptic plasma membranes of sheep brain cells was investigated with [ 125I]calmodulin. Calmodulin binding to these membranes is Ca 2+-dependent with a half maximal saturation at the pCa value of about 5.5. The binding is reduced by replacing Ca 2+ with Mg 2+, but it is significantly enhanced when both cations are present in the medium. Cation-dependent binding is specific and saturable with an apparent KD of about 47–50 nM and a maximal capacity of about 4 pmol mg −1 protein. The results indicate that synaptic plasma membranes isolated from sheep brain cells interact with calmodulin in a Ca 2+-dependent, Mg 2+-facilitated manner. 相似文献
12.
Dihydropyridine-sensitive Ca 2+ channels and the relationship between binding of dihydropyridine derivatives and depolarization-induced Ca 2+ uptake have been studied in aneurally cultured human muscle. Analysis of the equilibrium binding of the 1,4-dihydropyridine derivative (+)-PN200-110 revealed a single high-affinity binding site with a Kd of 0.15±0.05 nM and a Bmax of 87±12 fmol/mg protein. Inhibition of (+)-[ 3H]PN200-110 binding by nitrendipine revealed a Ki of 0.8 nM for the nitrendipine-receptor complex. Depolarization of cultured human muscle achieved by elevating the K + concentration increased the uptake 45Ca 2+ which was inhibited by nitrendipine with an IC 50 of 1.1 nM. This study demonstrates that aneurally cultured human muscle has dihydropyridine-sensitive voltage-dependent Ca 2+ channels which are functional when the fibers are depolarized. 相似文献
13.
We investigated the initiation of Ca 2+waves underlying triggered propagated contractions (TPCs) occurring in rat cardiac trabeculae under conditions that simulate the functional non-uniformity caused by mechanical or ischemic local damage of the myocardium. A mechanical discontinuity along the trabeculae was created by exposing the preparation to a small constant flow jet of solution with a composition that reduces excitation–contraction coupling in myocytes within that segment. Force was measured and sarcomere length as well as [Ca 2+] i were measured regionally. When the jet-contained Caffeine, BDM or Low-[Ca 2+], muscle-twitch force decreased and the sarcomeres in the exposed segment were stretched by shortening of the normal regions outside the jet. During relaxation the sarcomeres in the exposed segment shortened rapidly. Short trains of stimulation at 2.5 Hz reproducibly caused Ca 2+-waves to rise from the borders exposed to the jet. Ca 2+-waves started during force relaxation of the last stimulated twitch and propagated into segments both inside and outside of the jet. Arrhythmias, in the form of non-driven rhythmic activity, were triggered when the amplitude of the Ca 2+-wave increased by raising [Ca 2+] o. The arrhythmias disappeared when the muscle uniformity was restored by turning the jet off. We have used the four state model of the cardiac cross bridge (Xb) with feedback of force development to Ca 2+ binding by Troponin-C (TnC) and observed that the force–Ca 2+ relationship as well as the force–sarcomere length relationship and the time course of the force and Ca 2+ transients in cardiac muscle can be reproduced faithfully by a single effect of force on deformation of the TnC·Ca complex and thereby on the dissociation rate of Ca 2+. Importantly, this feedback predicts that rapid decline of force in the activated sarcomere causes release of Ca 2+ from TnC.Ca 2+,which is sufficient to initiate arrhythmogenic Ca 2+ release from the sarcoplasmic reticulum. These results show that non-uniform contraction can cause Ca 2+-waves underlying TPCs, and suggest that Ca 2+ dissociated from myofilaments plays an important role in the initiation of arrhythmogenic Ca 2+-waves. 相似文献
14.
Intravenous administration of ovokinin(2–7), a cleavage peptide derived from ovalbumin, dose-dependently (0.1–5 mg/kg) lowered the mean arterial pressure (MAP) that was not accompanied by a significant change in the heart rate (HR) of urethane-anesthetized rats. The hypotensive effects of ovokinin(2–7) were five orders of magnitude lower compared to that of bradykinin and were largely prevented by pretreatment with the bradykinin B 2 receptor antagonist HOE140 (81.6±18.4%) and moderately affected by the B 1 receptor antagonist [des-Arg 10]-HOE140 (26.3±15.5%). Intracellular Ca 2+ levels, as measured by Fur 2-AM, were significantly elevated in cultured aorta smooth muscle cells by ovokinin(2–7). The increases were abolished by HOE140 and unaffected by [des-Arg 10]-HOE140. The elevation of intracellular Ca 2+ by ovokinin(2–7) was dependent on Ca 2+ entry from extracellular space as it was reduced in a Ca 2+-free solution. Pretreatment of the cells with the phospholipase C inhibitor U73122 (2 μM) eliminated the Ca 2+ increase by the peptide. PA phosphohydrolase and phospholipase A 2 inhibitors significantly reduced the responses as well. Our results show that ovokinin(2–7) modulates cardiovascular activity by interacting with B 2 bradykinin receptors. 相似文献
15.
Adrenomedullin (ADM) is a hypotensive peptide, highly expressed in the mammalian adrenal medulla, which belongs to a peptide superfamily including calcitonin gene-related peptide (CGRP) and amylin. Quantitative autoradiography demonstrated the presence of abundant [ 125I]ADM binding sites in both zona glomerulosa (ZG) and adrenal medulla. ADM binding was selectively displaced by ADM(22–52), a putative ADM-receptor antagonist, and CGRP(8–37), a ligand that preferentially antagonizes the CGRP1-receptor subtype. ADM concentration-dependently inhibited K +-induced aldosterone secretion of dispersed rat ZG cells, without affecting basal hormone production. Both ADM(22–52) and CGRP(8–37) reversed the ADM effect in a concentration-dependent manner. ADM counteracted the aldosterone secretagogue action of the voltage-gated Ca 2+-channel activator BAYK-8644, and blocked K +- and BAYK-8644-evoked rise in the intracellular Ca 2+ concentration of dispersed ZG cells. ADM concentration-dependently raised basal catecholamine (epinephrine and norepinephrine) release by rat adrenomedullary fragments, and again the response was blocked by both ADM(22–52) and CGRP(8–37). ADM increased cyclic-AMP release by adrenal-medulla fragments, but not capsule-ZG preparations, and the catecholamine response to ADM was abolished by the PKA inhibitor H-89. Collectively, the present findings allow us to draw the following conclusions: (1) ADM modulates rat adrenal secretion, acting through ADM(22–52)-sensitive CGRP1 receptors, which are coupled with different signaling mechanisms in the cortex and medulla; (2) ADM selectively inhibits agonist-stimulated aldosterone secretion, through a mechanism probably involving the blockade of the Ca 2+ channel-mediated Ca 2+ influx; (3) ADM raises catecholamine secretion, through the activation of the adenylate cyclase/PKA signaling pathway. 相似文献
16.
The effect of clomiphene, an ovulation-inducing agent, on cytosolic free Ca 2+ levels ([Ca 2+] i) in populations of PC3 human prostate cancer cells was explored by using fura-2 as a Ca 2+ indicator. Clomiphene at concentrations between 10-50 μM increased [Ca 2+] i in a concentration-dependent manner. The [Ca 2+] i signal was biphasic with an initial rise and a slow decay. Ca 2+ removal inhibited the Ca 2+ signal by 41%. Adding 3 mM Ca 2+ increased [Ca 2+] i in cells pretreated with clomiphene in Ca 2+-free medium, confirming that clomiphene induced Ca 2+ entry. In Ca 2+-free medium, pretreatment with 50 μM brefeldin A (to permeabilize the Golgi complex), 1 μM thapsigargin (to inhibit the endoplasmic reticulum Ca 2+ pump), and 2 μM carbonylcyanide m-chlorophenylhydrazone (to uncouple mitochondria) inhibited 25% of 50 μM clomiphene-induced store Ca 2+ release. Conversely, pretreatment with 50 μM clomiphene in Ca 2+-free medium abolished the [Ca 2+] i increase induced by brefeldin A, thapsigargin or carbonylcyanide m-chlorophenylhydrazone. The 50 μM clomiphene-induced Ca 2+release was unaltered by inhibiting phospholipase C with 2 μM 1-(6-((17β-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione (U73122). Trypan blue exclusion assay suggested that incubation with clomiphene (50 μM) for 2-15 min induced time-dependent decrease in cell viability by 10-50%. Collectively, the results suggest that clomiphene induced [Ca 2+] i increases in PC3 cells by releasing store Ca 2+ from multiple stores in an phospholipase C-independent manner, and by activating Ca 2+ influx; and clomiphene was of mild cytotoxicity. 相似文献
17.
In this study we investigated the release of Ca 2+ in brain microsomes after Ca 2+ loading by the Ca 2+-ATPase or by the Na +/Ca 2+ exchanger. The results show that in microsomes loaded with Ca 2+ by the Ca 2+-ATPase, Ins(1,4,5)P 3 (5 μM) release 21±2% of the total Ca 2+ accumulated, and that in the microsomes loaded with Ca 2+ by the Na 2+/Ca 2+ exchanger, Ins(1,4,5)P 3 released 28±3% of the total Ca 2+ accumulated. These results suggest that receptors of Ins(1,4,5)P 3 may be co-localized with the Na 2+/Ca 2+ exchanger in the endoplasmic reticulum membrane or that there are Ins(1,4,5)P 3 receptors in the plasma membrane where the Na 2+/Ca 2+ exchanger is normally present, or both. We also found that Ins(1,4,5)P 3 inhibited the Ca 2+-ATPase by 33.7%, but that it had no significant effect on the Na 2+/Ca 2+ exchanger. 相似文献
18.
The store-mediated Ca 2+ entry was detected in single and cluster of rat submandibular acinar cells by measuring the Ca 2+ activated ionic membrane currents. In the cells where intracellular Ca 2+ was partly depleted by stimulation with submaximal concentration of acetylcholine (ACh) under a Ca 2+-free extracellular condition, an employment of external Ca 2+ in the absence of ACh caused a sustained increase of the K + current without affecting the Cl − current. A renewed ACh challenge without external Ca 2+ caused repetitive spikes of both K + and Cl − currents due to the Ca 2+ release. SK & F 96365 inhibited the generation of the sustained K + current and refilling of the Ca 2+ store following the Ca 2+ readmission. It is suggested that the Ca 2+ enters the cell through the store-mediated pathway near the K + channels and is taken up by the store. Thus, only Ca 2+ released from the store can activate both the K + and Cl − currents. 相似文献
19.
Fluoxetine, a selective 5-HT uptake inhibitor, inhibited 15 mM K +-induced [ 3H] 5-HT release from rat spinal cord and cortical synaptosomes at concentrations > 0.5 uM. This effect reflected a property shared by another selective 5-HT uptake inhibitor paroxetine but not by less selective uptake inhibitors such as amitriptyline, desipramine, imipramine or nortriptyline. Inhibition of release by fluoxetine was inversely related to both the concentration of K + used to depolarize the synaptosomes and the concentration of external Ca 2+. Experiments aimed at determining a mechanism of action revealed that fluoxetine did not inhibit voltage-independent release of [ 3H] 5-HT release induced by the Ca 2+-ionophore A 23187 or Ca 2+-independent release induced by fenfluramine. Moreover the 5-HT autoreceptor antagonist methiothepin did not reverse the inhibitory actions of fluoxetine on K +-induced release. Further studies examined the effects of fluoxetine on voltage-dependent Ca 2+ channels and Ca 2+ entry. Whereas fluoxetine and paroxetine inhibited binding of [ 3H] nitrendipine to the dihydropyridine-sensitive L-type Ca 2+ channel, the less selective uptake inhibitors did not alter binding. The dihydropyridine antagonist nimodipine partially blocked fluoxetine-induced inhibition of release. Moreover enhanced K +-stimulated release due to the dihydropyridine agonist Bay K 8644 was reversed by fluoxetine. Fluoxetine also inhibited the K +-induced increase in intracellular free Ca 2+ in fura-2 loaded synaptosomes. These data are consistent with the suggestion that fluoxetine inhibits K +-induced [ 3H] 5-HT release by antagonizing voltage-dependent Ca 2+ entry into nerve terminals. 相似文献
20.
The preservative, methylhydroxybenzoate inhibited O 2- secretion from human neutrophils activated by both the chemotactic peptide fMet-Leu-Phe and phorbol myristate acetate (PMA): the low level of oxidant secretion activated by the ionophore A23187 was similarly reduced in preservative-treated suspensions. Oxidant secretion was similarly reduced in fMet-Leu-Phe and A23187 treated suspensions in which intracellular Ca 2+ was buffered by loading with Quin-2, indicating that methylhydroxybenzoate may exert its effects by perturbation of intracellular Ca 2+ -dependent processes. Methylhydroxybenzoate could mimic EGTA in preventing the Ca 2+ dependent enhancement of trypsin activity and could also bind this cation in experiments using a Ca 2+ electrode, although the preservative bound Ca 2+ more slowly and had a lower affinity than EGTA. These data indicate that methylhydroxybenzoate may exert its effects on neutrophils by perturbation of Ca 2+-dependent activation pathways and this phenomenon may also explain its other known pharmacological effects. Furthermore, these observations provide an insight into the mechanisms by which intracellular Ca 2+ may regulate oxidant secretion. 相似文献
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