受体酪氨酸激酶抑制剂linifanib的合成

目的合成受体酪氨酸激酶抑制剂linifanib。方法以2-氟-5-甲基苯胺为起始原料,经3步反应制得中间体Ⅳ．（4．硼酸频哪醇酯苯基）-N＇-（2-氟-5-甲基苯基）脲（5）;以2,6-二氯苯腈为起始原料,经关环反应制得另一中间体3-氨基-4-氯-吲唑（7）;中间体5和7经Suzuki偶联反应得到目标化合物linifanib。结果与结论目标化合物和中间体的结构经1H—NMR、MS谱确证,总收率为11．4％。     

克里唑替尼的合成工艺研究

目的研究克里唑替尼的合成工艺。方法以2,6-二氯-3-氟苯乙酮为起始原料,经还原、手性拆分、Mitsunobu反应、还原、溴代得中间体(R)-5-溴-3-(1-(2,6-二氯-3-氟苯基)乙氧基)-吡啶-2-胺,然后该中间体与1-(N-Boc-4-哌啶基)吡唑-4-硼酸频哪醇酯经Suzuki反应、脱除Boc保护基得到目标化合物克里唑替尼。结果与结论目标化合物的结构经1H-NMR、13C-NMR、MS及IR确证。总收率达14.6%(以2,6-二氯-3-氟苯乙酮计)。该路线原料易得、操作简便、条件温和、收率较高,为工业化生产奠定一定的基础。     

非放射性氟代乙酸的氟标记合成反应研究

目的用新工艺实现氟代乙酸的氟标记合成。方法以对硝基苯磺酰氯和羟基乙酸乙酯为原料,合成2-（4-硝基）-苯磺酸酯基乙酸乙酯,以此作为中间体,模拟F-18↑F自动化放化合成的氟化反应条件合成氟乙酸乙酯,对产物进行高效液相色谱-质谱、核磁共振谱（NMR）分析。结果中间体2-（4-硝基）-苯磺酸酯基乙酸乙酯产率可达79.38%,以此作为中间体可以实现非放射性F-氟化反应合成18↑F-氟代乙酸乙酯,HPLC-MS及NMR分析表明其就是目标产物。结论以2-（4-硝基）-苯磺酸酯基乙酸乙酯作为前体进行F-18↑F全自动化氟化反应合成18F-氟代乙酸盐可行。     

芳基哒嗪酮酸姜黄素酯的合成

目的:合成芳基哒嗪酮酸姜黄素酯。方法:以5-甲基-2-(3-氯-4-氟苯基)-2-氧代哒嗪酸(化合物1)和姜黄素为原料,在N,N-二环己基碳二酰亚胺(DCC)/4-二甲氨基吡啶(DMAP)催化下,姜黄素两侧酚羟基与哒嗪酮6位羧基双侧成酯。经柱层析分离,得到目标产物,质谱和核磁表征其结构,并单因素考察原料配比、反应温度、反应时间、催化剂对反应的影响。结果:经表征,目标产物即芳基哒嗪酮酸姜黄素酯,产率为56.3%(以姜黄素计),高效液相色谱法测得含量为98.1%。最优反应条件为姜黄素-化合物1的配比为1∶3,反应温度为50℃,反应时间为10 h,催化剂为DCC/DMAP。结论:成功合成芳基哒嗪酮酸姜黄素酯,且工艺稳定。     

对羟基苯硼酸频哪醇酯的合成

用叔丁基二甲基氯硅烷保护对溴苯酚的酚羟基,制成Grignard试剂后与硼酸三甲酯反应制得对叔丁基二甲基硅氧基苯硼酸二甲酯,再与频哪醇进行酯交换反应后脱去保护基得到对羟基苯硼酸频哪醇酯,总收率28.2%.     

自动化合成N-琥珀酰亚胺-4-[18F]氟苯甲酸酯

目的 合成18F同位素标记蛋白质、配体、多肽类的中间体N-琥珀酰亚胺-4-[18F]氟苯甲酸酯(18F-FB).方法 以乙基-4-三甲胺苯甲酸酯-三氟磺酸盐为反应前体,利用正电子发射断层成像(PET)显像药物2-氟-18-氟-2-脱氧-D-葡萄糖(18F-FDG)合成专用模块TRACERlab FX-FDG和多用合成模块TRACERlab FX-FN及其固相萃取系统,基于控制软件的改造,通过亲核取代、氢氧化钠水解、酯化反应"三步法"合成.结果 合成18F-FB的总放射性合成时间小于80 min,校正后放射化学产率(38±3)%(n=10),放射化学纯度＞99%,与标准品19F-FB行HPLC比对分析,在柱平均保留时间Tr=8.515 min,两者保留时间基本吻合.结论 此法可以成功合成18F-FB,合成工艺成熟稳定,完全实现了自动化合成,为成功实现18F同位素标记蛋白、多肽类大分子物质进而实现PET成像提供了良好条件.     

二氟泼尼酯的合成

目的合成二氟泼尼酯。方法以6α,9α-二氟泼尼龙为起始原料,经酯化、水解、乙酰化得到二氟泼尼酯。结果合成了二氟泼尼酯。结论目标化合物结构经MS、1H-NMR确证,该反应路线操作简洁,总收率为67.1%。     

选择性COX-2抑制剂NS-398的制备

目的制备选择性COX-2抑制剂NS-398。方法以2-氟硝基苯为起始原料,经4步反应化合成化合物NS-398。结果与结论用该方法可以在温和条件下合成出该药,最终产品纯度大于99%。     

4-(4,6-二吗啉-1,3,5-三嗪-2-基)苯胺的合成

目的合成4-(4,6-二吗啉-1,3,5-三嗪-2-基)苯胺。方法三氯聚氰与吗啉在冰浴条件下经取代反应制得4,4’-(6-氯-1,3,5-三嗪-2,4-二基)二吗啉,再与苯胺-4-硼酸频那醇酯经Suzuki反应制得4-(4,6-二吗啉-1,3,5-三嗪-2-基)苯胺。结果与结论结构经核磁及质谱确证,总收率约61.7%。     

(1R,2R)-1,2-环己烷二甲醇二甲磺酸酯的合成

目的:合成(1R,2R)-1,2-环己烷二甲醇二甲磺酸酯(化合物1)。方法:以(±)-反式-4-环己烯-1,2-二甲酸(化合物2)为原料,经钯碳还原、(R)-1-苯乙胺拆分、在甲醇中与氯化亚砜反应、硼氢化钠-无水氯化锂还原、甲基磺酰氯反应得到目标化合物,并进行核磁共振(1H-NMR)或质谱(MS)表征。以(1R,2R)-1,2-环己烷二甲酸(化合物4)/氯化亚砜的投料比、反应温度和时间对酰化反应进行优化,以化合物4/硼氢化钠/无水氯化锂的投料比、反应温度和时间、溶剂对酯还原反应进行优化,筛选(1R,2R)-1,2-环己烷二甲醇(化合物5)的合成条件。结果:表征确证目标化合物为化合物1,总收率为27.9%,纯度>99%。化合物5的合成中,酰化反应条件为化合物4/氯化亚砜投料比为1.0:2.2,反应温度为65℃,反应时间为2h;酯还原反应条件为化合物4/硼氢化钾/无水氯化锂投料比为1.0:3.0:3.0,反应温度为20～30℃,反应时间为24h,溶剂为四氢呋喃。结论:所建立的反应条件温和、操作简便易行,各步原料价格低廉。     

Inhibition of Na+-pump enhances carbachol-induced influx of 45Ca2+ and secretion of catecholamines by elevation of cellular accumulation of 22Na+ in cultured bovine adrenal medullary cells

Summary In bovine adrenal medullary cells, we reported that ²²Na⁺ influx via nicotinic receptor-associated Na⁺ channels is involved in ⁴⁵Ca²⁺ influx, a requisite for initiating the secretion of catecholamines (Wada et al. 1984, 1985b).In the present study, we investigated whether the inhibition of Na⁺-pump modulates carbachol-induced ²²Na⁺ influx, ⁴⁵Ca²⁺ influx and catecholamine secretion in cultured bovine adrenal medullary cells. We also measured ⁸⁶Rb⁺ uptake by the cells to estimate the activity of Na⁺, K⁺-ATPase. (1) Ouabain and extracellular K⁺ deprivation remarkably potentiated carbachol-induced ²²Na⁺ influx, ⁴⁵Ca²⁺ influx and catecholamine secretion; this potentiation of carbachol-induced ⁴⁵Ca²⁺ influx and catecholamine secretion was not observed in Na⁺ free medium. (2) Carbachol increased the uptake of ⁸⁶Rb⁺; this increase was inhibited by hexamethonium and d-tubocurarine. In Na⁺ free medium, carbachol failed to increase ⁸⁶Rb⁺ uptake. (3) Ouabain inhibited carbachol-induced ⁸⁶Rb⁺ uptake in a concentration-dependent manner, as it increased the accumulation of cellular ²²Na⁺. These results suggest that Na⁺ influx via nicotinic receptor-associated Na⁺ channels increases the activity of Na⁺, K⁺-ATPase and the inhibition of Na⁺, K⁺-ATPase augmented carbachol-induced Ca²⁺ influx and catecholamine secretion by potentiating cellular accumulation of Na⁺. It seems that nicotinic receptor-associated Na⁺ channels and Na⁺, K⁺-ATPase, both modulate the influx of Ca²⁺ and secretion of catecholamines by accomodating cellular concentration of Na⁺.     

Radiopharmaceutical chemistry for positron emission tomography

Molecular imaging is an emerging technology that allows the visualization of interactions between molecular probes and biological targets. Molecules that either direct or are subject to homeostatic controls in biological systems could be labeled with the appropriate radioisotopes for the quantitative measurement of selected molecular interactions during normal tissue homeostasis and again after perturbations of the normal state. In particular, positron emission tomography (PET) offers picomolar sensitivity and is a fully translational technique that requires specific probes radiolabeled with a usually short-lived positron-emitting radionuclide. PET has provided the capability of measuring biological processes at the molecular and metabolic levels in vivo by the detection of the gamma rays formed as a result of the annihilation of the positrons emitted. Despite the great wealth of information that such probes can provide, the potential of PET strongly depends on the availability of suitable PET radiotracers. However, the development of new imaging probes for PET is far from trivial and radiochemistry is a major limiting factor for the field of PET. In this review, we provided an overview of the most common chemical approaches for the synthesis of PET-labeled molecules and highlighted the most recent developments and trends. The discussed PET radionuclides include ¹¹C (t_1/2 = 20.4 min), ¹³N (t_1/2 = 9.9 min), ¹⁵O (t_1/2 = 2 min), ⁶⁸Ga (t_1/2 = 68 min), ¹⁸F (t_1/2 = 109.8 min), ⁶⁴Cu (t_1/2 = 12.7 h), and ¹²⁴I (t_1/2 = 4.12 d).     

Some degree of overlap exists between the K+-channels opened by cromakalim and those opened by minoxidil sulphate in rat isolated aorta

Summary The effects of the K⁺ channel opening drugs minoxidil sulphate and cromakalim, on ⁴²K⁺ and ⁸⁶Rb⁺ efflux and on vasorelaxation in rat isolated aorta, were compared. In rat aortic rings precontracted with noradrenaline (100 nmol/l), minoxidil sulphate and cromakalim concentration-dependently inhibited induced tension by up to 90%, with pD₂ values of 7.35±0.1 and 7.17±0.1, respectively. Glibenclamide (300 nmol/l), produced 2200- and 19-fold rightward shifts in the concentration-relaxation curves to minoxidil sulphate and cromakalim, respectively, without an effect on the maximum relaxation.Both minoxidil sulphate and cromakalim increased the efflux of ⁴²K⁺ and ⁸⁶Rb⁺ from aorta in a concentration-dependent manner, with midpoints in the µmol/l range; the maximum efflux induced by minoxidil sulphate being approximately one tenth of that induced by cromakalim. The ratio of stimulated ⁸⁶Rb⁺/⁴²K⁺ efflux increased from 0.22 to 0.48 with increasing cromakalim concentrations, but was approximately constant (0.39) when the minoxidil sulphate concentration was varied. In the presence of minoxidil sulphate, the effects of cromakalim on ⁴²K⁺ and ⁸⁶Rb⁺ efflux were inhibited in a concentration-dependent manner, by up to 60%. In the continuing presence of cromakalim (300 nmol/l), minoxidil sulphate (10 µmol/l)-induced increases in ⁴²K⁺ and ⁸⁶Rb⁺ efflux were inhibited by 45%, whereas conditioning with cromakalim (1 µmol/l) inhibited the ⁸⁶Rb⁺ efflux stimulated by additional superfusion of cromakalim (1 µmol/l) by 85%. Glibenclamide inhibited minoxidil sulphate (10 µmol/l)- and cromakalim (1 µmol/l)-induced increases in ⁴²K⁺ and ⁸⁶Rb⁺ efflux in a concentration-dependent manner with IC₅₀ values of approximately 80 nmol/l.In conclusion, the efflux data suggest that considerable overlap exists between the channels opened by minoxidil sulphate and those opened by cromakalim in rat aorta. Minoxidil sulphate has a weak efficacy as a K⁺ channel opener, and may act to open a homogeneous population of K⁺ channels. In contrast, the actions of cromakalim (1 µmol/l) are associated with large increases in tracer efflux, which are probably mediated via a heterogeneous population of K⁺ channels. However, only a small proprtion of this induced efflux appears to be required for relaxation. The differential inhibition by glibenclamide of the vasorelaxant effects of minoxidil sulphate and cromakalim may result from (a) the partial agonist properties of minoxidil sulphate in opening K⁺ channels and/or (b) additional mechanisms of vasorelaxation, which differ in their sensitivity to glibenclamide. Send offprint requests to U. Quasi at the above address     

Role of Na+ and protein kinase C in angiotensin desensitization and tachyphylaxis in the guinea-pig ileum

Summary Simultaneous recordings of the tension and intracellular Ca²⁺ concentration of guinea-pig ileum longitudinal smooth muscle strips, as well as ²⁴Na⁺ and ⁴⁵Ca²⁺ influx measurements in cultured myocytes from the same tissue, were used to investigate the mechanisms underlying angiotensin-induced desensitization and tachyphylaxis. Angiotensin II and [2-lysine]-angiotensin II (Lys²All), incubated for prolonged periods (10 min) with muscle strips, induced fading of the contractile response (desensitization) and reappearance of the intracellular Ca²⁺ concentration oscillations, which were inhibited during the initial increase in cytosolic Ca²⁺. The desensitization was paralleled, in cultured myocytes, by inhibition of the ⁴⁵Ca²⁺ but not of the ²⁴Na⁺ influxes which were initially stimulated by the peptides. On the other hand, repeated administrations of angiotensin II (but not of Lys²All) caused gradual reduction of the contractile response and of the ²⁴Na⁺ influx stimulation evoked by the agonist (tachyphylaxis). Treatment with phorbol 12–13 dibutyrate accelerated the desensitization induced by both angiotensin II and by Lys²All and aggravated the tachyphylaxis to angiotensin II. The results support the hypothesis that activation of protein kinase C is responsible for the desensitization and that tachyphylaxis is due to the slow dissociation of angiotensin II from a postulated Na⁺-dependent regulatory site on the receptor.Correspondence to S.I. Shimuta at the above address     

Distribution of 2, 21,4,41, 5,51-hexaehlorobiphenyl in mice and Chinese Hamsters

The distribution of 2,2¹,4,4¹,5,5¹-hexachlorobiphenyl-¹⁴C was studied in mice and Chinese Hamsters using whole body autoradiography and liquid scintillation counting. The mice exhibited a strong and persistent accumulation of radioactivity in the bronchial mucosa, and this accumulation was not fully developed until about 24 hrs after an intravenous injection. The labelled substance passed to the fetuses of pregnant mice and was also concentrated in the fetal bronchi. Mice pretreated with a large dose of unlabelled PCB per os in peanut oil showed a completely different distribution pattern in the lungs — only traces of label being taken up by the bronchi. Quantitative measurements revealed a concomitant reduction of the total radioactivity retained by the lungs. Except for the lungs, however, no major differences in the distribution pattern were found at the various dose levels. The distribution in the Chinese hamsters equaled approximately that of the mice, but a very weak accumulation of label was observed in the hamster bronchi. The radioactivity in the mouse bronchi was considered as perhaps representing metabolized PCB.     

Decontamination of rat and human skin experimentally contaminated with 99mTc, 201Tl and 131I radionuclides using “Dermadecon” – a skin decontamination kit: an efficacy study

Radioactive skin contamination is one of the most likely risks which occurs after accidental or occupational radiological accidents apart from internal contamination. In such cases where the radioactive contamination has occurred, the person who is contaminated should be decontaminated as early as possible to reduce the damaging health effects of radiation. In the present study, the decontamination efficiency of a developed skin decontamination kit “dermadecon” has been evaluated in animal models and human subjects using gamma scintigraphy. Decontamination efficiency (percentage of the radioactive contaminant removed) was calculated for each radioactive isotope of the study and compared with control where general washing procedure was followed using liquid and soap. The effectiveness of the kit was calculated in animal model with respect to ^99mTc-sodium-pertechnetate (^99mTcO^4?), ²⁰¹TlCl and ¹³¹I and was found 92.84?±?4.9%, 91.18?±?3.23% and 94.67?±?2.92%, respectively. Whereas, in case of human skin, the decontamination efficiency for ^99mTcO^4? was observed to be 95.00?±?3.21%. On the basis of findings from the study, it can be concluded that the decontamination agents of the used skin decontamination kit are effective for removal of localized radioactive contaminants from skin, as compared with normal decontamination using soap and water.     

Effects of propylthiouracil and methylthiouracil on cyclic AMP and ion movements in rat pancreatic islets

Summary Propylthiouracil and methylthiouracil have been shown to potentiate glucose-induced insulin secretion from rat pancreatic islets: the effect of methylthiouracil being less pronounced than that of propylthiouracil. In this study the effects of these substances on cAMP levels, ⁸⁶Rb⁺ efflux, ⁴⁵Ca²⁺ net uptake, and ⁴⁵Ca²⁺ efflux were tested in isolated rat islets in order to obtain information on their possible mechanism of action. Propylthiouracil and to a lesser extent methylthiouracil increased islet cyclic AMP in a concentration-related manner. Maximum increases at the highest concentrations tested were 261% and 190% respectively. In the presence of 3 mM glucose propylthiouracil and methylthiouracil led to a decrease in the ⁸⁶Rb efflux rate. With 5.6 mM glucose, both thiourea derivatives produced an increase in the ⁸⁶Rb⁺ efflux rate which was independent of the presence or absence of calcium in the medium. Propylthiouracil and methylthiouracil augmented the ⁴⁵Ca²⁺ efflux rate in the presence as well as in the absence of external calcium at various glucose concentrations. Propylthiouracil did not change, and methylthiouracil only slightly augmented, ⁴⁵Ca²⁺ net uptake into the isolated islets. It is suggested that the synergistic effect of propylthiouracil and methylthiouracil on glucose-induced insulin release is at least in part due to an increase in islet cAMP levels. Whether the two substances have additional direct effects on ionic fluxes which contribute to their insulinotropic action or whether the observed changes in ion movements are secondary to the elevation of cAMP levels remains to be unclear and needs further investigation. Send offprint requests to H. P. T. Ammon at the above address     

Comparison of the effluxes of 42K+ and 86Rb+ elicited by cromakalim (BRL 34915) in tonic and phasic vascular tissue

Summary The cromakalim-induced effluxes of ⁴²K⁺ and ⁸⁶Rb⁺ were compared in rat aortic segments and in guinea-pig portal vein. In both vessels, low concentrations of cromakalim (0.1 M) increased the permeability to ⁸⁶Rb⁺ 3–4 times less than that to ⁴²K⁺; at 10 M the difference was about a factor of 1.3–2. In rat aorta, the threshold concentration of cromakalim for ⁴²K⁺ efflux was 0.03 M; with ⁸⁶Rb⁺ as the tracer ion it was 0.1 M. At similar concentrations, cromakalim relaxed the tension of aortic segments precontracted with 23 mM KCl (IC₅₀ = 0.06 ± 0.01 M). However, no concomitant increase in ⁴²K⁺ or ⁸⁶Rb⁺ efflux could be detected from this stimulated preparation at these concentrations. In guinea-pig portal vein, ⁴²K⁺ efflux measurements were performed in the presence and absence of the dihydropyridine Ca²⁺ entry blocker PN 200-110 (isradipine) yielding comparable results. In the presence of PN 200-110, where spontaneous activity and the K⁺ efflux associated with it were abolished, the threshold concentration of cromakalim for ⁴²K⁺ efflux was 0.02 M as compared to 0.06 M for ⁸⁶Rb⁺ efflux. In the absence of PN 200-110, spontaneous activity of the portal vein was inhibited by 70% and 90% at these concentrations. In double isotope experiments, the K⁺ channel inhibitor tetraethylammonium did not discriminate between the effluxes of ⁴²K⁺ and ⁸⁶Rb⁺ stimulated by cromakalim.It is concluded that in the two vascular tissues examined, cromakalim increased the permeability to ⁴²K⁺ more than to ⁸⁶Rb⁺, the difference being more marked at low cromakalim concentrations. The use of ⁴²K⁺ as the tracer ion narrows the apparent gap between the concentrations of cromakalim which elicit vasorelaxant effects and those which induce an observable increase in K⁺ permeability; however a significant difference persists.Part of the data was presented at the Winter Meeting of the British Pharmacological Society London 1988 [Br J Pharmacol 93 (1988) p 19] Send offprint requests to U. Quasi at the above address     

On the mechanism of action of phenylephrine in rat atrial heart muscle

Both in rat left atrial heart and in aortic smooth muscle preparations, phenylephrine (PE) caused a concentration-dependent increase in force of contraction (F_c) in the presence of atenolol (10 mol/l), which was antagonized by phentolamine, prazosin and WB 4101 in a competitive manner. The pA₂ values of the antagonists in the cardiac tissue were 10–20fold lower than those in the rat thoracic aorta. In the spontaneously beating right atrium, PE exerted a positive chronotropic action, which was not significantly antagonized by phentolamine or prazosin. It is therefore assumed that the effects of phenylephrine in the left atrium and in the aorta are mediated by different subtypes of ₁-adrenoceptors, whereas the effects in the sino-atrial node are probably unrelated to ₁-adrenoceptors. To further elucidate the mechanisms of the positive inotropic effect of PE, action potential configuration and ⁴⁵Ca²⁺ fluxes were monitored in the rat left atrium. The increase in F_c by PE was associated with an increase in action potential duration (APD) and a reduction in resting membrane potential (RP). In the presence of (–)-devapamil (13888), the effects of PE on APD and RP persisted, whereas the increase in F_c was antagonized in a non-competitive manner. Forskolin (300 nmol/l) enhanced the positive inotropic effect of PE. PE exerted a significant increase in ⁴⁵CA²⁺ uptake in beating preparations, which was abolished in the presence of (–)13888 (1 mol/l). In addition to the PE-induced increase in ⁴⁵Ca²⁺ uptake, a decrease in ⁴⁵Ca²⁺ efflux was observed. Similarly, depolarization of the membrane by raising [K⁺]_o to 85 mmol/l revealed an increase in ⁴⁵Ca²⁺ uptake and a decrease in ⁴⁵Ca²⁺ efflux. The latter observations support the view that the membrane potential strongly determines the movement of ⁴⁵Ca²⁺ across the membrane. It is assumed that the ₁-adrenoceptor-mediated changes in APD and RP may enhance F_c, first, by increasing net Ca²⁺ entry from the extracellular space through voltage-dependent Ca²⁺ channels and, second, by decreasing Ca²⁺ efflux possibly via the Na ⁺/Ca²⁺ exchange mechanism.     

Molecular and functional characterization of the human platelet Na(+) /Ca(2+) exchangers

BACKGROUND AND PURPOSE The Na(+) /Ca(2+) exchanger is a bi-directional transporter that plays an important role in maintaining the concentration of cytosolic Ca(2+) ([Ca(2+) ](i) ) of quiescent platelets and increasing it during activation with some, but not all, agonists. There are two classes of Na(+) /Ca(2+) exchangers: K(+) -independent Na(+) /Ca(2+) exchanger (NCX) and K(+) -dependent Na(+) /Ca(2+) exchanger (NCKX). Platelets have previously been shown to express NCKX1. However, initial studies from our laboratory suggest that NCX may also play a role in platelet activation. The objective of this study was to determine if the human platelet expresses functional NCXs. EXPERIMENTAL APPROACH RT-PCR, DNA sequencing and Western blot analysis were utilized to characterize the human platelet Na(+) /Ca(2+) exchangers. Their function during quiescence and collagen-induced activation was determined by measuring [Ca(2+) ](i) with calcium-green/fura-red in response to: changes in the Na(+) and K(+) gradient, NCX pharmacological inhibitors (CBDMB, KB-R7943 and SEA0400) and antibodies specific to extracellular epitopes of the exchangers. KEY RESULTS Human platelets express NCX1.3, NCX3.2 and NCX3.4. The NCXs operate in the Ca(2+) efflux mode in resting platelets and also during their activation with thrombin but not collagen. Collagen-induced increase in [Ca(2+) ](i) was reduced with the pharmacological inhibitors of NCX (CBDMB, KB-R7943 or SEA0400), anti-NCX1 and anti-NCX3. In contrast, anti-NCKX1 enhanced the collagen-induced increase in [Ca(2+) ](i) . CONCLUSIONS AND IMPLICATIONS Human platelets express K(+) -independent Na(+) /Ca(2+) exchangers NCX1.3, NCX3.2 and NCX3.4. During collagen activation, NCX1 and NCX3 transiently reverse to promote Ca(2+) influx, whereas NCKX1 continues to operate in the Ca(2+) efflux mode to reduce [Ca(2+) ](i) .