黔西南北盘江镇喀斯特高原峡谷区植被演替阶段碳氮稳定同位素特征

为了探究森林不同演替阶段碳氮(C、N)、稳定碳氮同位素值(δ¹³C、δ¹⁵N)随演替发生的变化特征与内在联系,该文以喀斯特高原峡谷区草灌、灌木、乔灌和乔木4个演替阶段的森林植物群落为研究对象,测定了叶片-凋落物-土壤的C、N及稳定同位素值,并分析其在不同层次间的互作效应。结果表明:(1)喀斯特地区森林叶片-凋落物-土壤δ¹³C值分别为-31.31‰～-28.23‰、-29.96‰～-20.07‰、-26.83‰～-21.14‰,相应的δ¹⁵N值依次为-3.41‰～1.54‰、-2.61‰～0.99‰、5.36‰～8.63‰,总体上土壤表现出富集效应。(2)伴随着演替发生,叶片δ¹³C值与土壤δ¹⁵N值均为先减小后增大,土壤、凋落物δ¹³C值呈降低趋势,叶片和凋落物δ¹⁵N值均无明显变化规律。(3)乔灌阶段叶片-土壤δ¹⁵N值最低,表明该阶段生态系统N饱和程度较小,N含量相对亏缺。(4)叶片-土壤C、N及稳定同位素之间相关性较强,表明两者间养分循环紧密相关,具有显著抑制或促进效应。综上认为,该区生态系统修复时,应选择水分利用效率高的川钓樟(Lindera pulcherima)、圆叶乌桕(Triadica rotundifolia)、翅荚香槐(Cladrastis platycarpa)等树种,提高生态系统对资源利用和养分吸收的自调控能力。     

柴达木盆地白刺叶片δ13C与叶片和土壤养分指标的关系

在青海省柴达木盆地选择6个重要的唐古特白刺分布区域,通过测定不同白刺居群的叶片营养元素、土壤养分含量和叶片碳同位素组成δ¹³C,对比不同白刺居群间的叶片δ¹³C特征差异,并分析白刺叶片δ¹³C与地理位置信息及叶片营养和土壤养分含量指标的关系。结果显示:（1）白刺居群间叶片δ¹³C存在显著空间变异性,其叶片δ¹³C变化范围在-25.47‰~-27.66‰之间,平均为-26.66‰。(2）纬度、经度和海拔是白刺叶片δ¹³C重要影响因子,白刺叶片δ¹³C与纬度、经度和海拔分别呈极显著负相关,正相关和正相关关系（n=10）。（3）白刺叶片δ¹³C与叶片有机C含量、N、P、K含量总体均呈负相关关系,但仅叶片有机C含量达到极显著水平（n=30）,其余均未达到显著性水平（n=30）。（4）叶片δ¹³C与表层土壤（0~15 cm）有机质、全N、速效K含量呈极显著负相关关系（n=30）,与全P、碱解N和有效P含量呈显著负相关关系（n=30）,并与15~30 cm土壤有机质和全N含量显著负相关（n=30）,但叶片δ¹³C与30~45 cm土壤各化学指标相关性均不显著（n=30）。研究表明,环境因子纬度、经度、海拔,叶片有机C含量,以及立地土壤全N、全P、碱解N、有效P、速效K含量的变化均显著影响柴达木盆地唐古特白刺居群叶片δ¹³C值。     

粤北低山林地改建梯田对土壤碳、氮、磷及其化学计量特征的影响

为了阐明土地利用方式转变对土壤碳、氮、磷及其化学计量特征的影响,以粤北低山区4种土地利用方式:自然林地、坡地果园、旱作梯田和稻作梯田为研究对象,探索20年生林地向梯田转变后土壤有机碳(OC)、全氮(TN)和全磷(TP)的含量、储量及化学计量变化特征。结果表明: 土地利用转变明显改变了土壤碳、氮、磷含量和化学计量特征,随着土壤深度增加,旱作梯田和稻作梯田OC、TN含量呈显著下降趋势,自然林地和坡地果园呈“V”字型变化趋势,4种土地利用方式TP变化趋势不明显。土壤剖面OC含量以稻作梯田最高,均值为12.36 g·kg^-1,其次为林地(10.32 g·kg^-1)和旱作梯田(8.80 g·kg^-1),坡地果园最低(5.96 g·kg^-1);TN含量表现为稻作梯田(1.01 g·kg^-1)>旱作梯田(0.78 g·kg^-1)>林地(0.66 g·kg^-1)>坡地果园(0.33 g·kg^-1);TP含量以旱作梯田(0.71 g·kg^-1)最高,坡地果园(0.22 g·kg^-1)最低。4种土地利用方式土壤C∶N为8.87～22.94,以坡地果园土壤最高;C∶P为8.73～81.74,N∶P为0.77～5.13,均以林地土壤最高。土地利用方式、土壤深度及两者交互作用显著影响土壤碳、氮、磷及其化学计量特征,而土壤容重、pH值和黏粒含量也是重要的影响因素。研究结果可为粤北低山林地的土地利用和梯田生态系统的合理施肥提供科学依据。     

黄土高原小流域土壤养分空间变异特征及预测

在黄土高原小流域尺度上,地形和土地利用是影响土壤属性变异的重要因素.在横山县朱家沟小流域采集111个表层土样,比较不同土地利用及景观位置土壤养分变异及分布特征,分析土壤养分与地形因素的关系并利用相关环境信息进行空间预测.结果表明,不同土地利用类型土壤养分存在显著性差异.有机质和全氮含量表现为坝地最高,灌木地最低,而全磷含量以梯田最高.在不同景观位置,沟平地有机质和全氮含量显著高于其他景观位置,而全磷差异不显著.土壤有机质与复合地形指数CTI、汇流动力SPI、沉积物运移指数STI显著负相关,全氮与沉积物运移指数STI显著负相关,而全磷只与坡度β显著负相关.多元线性逐步回归模型预测土壤有机质和全氮较好,而全磷预测结果较差;回归-克里格预测有效地减小了残差,与实测值较为接近,预测精度高于回归预测.     

长白山苔原带凋落物生态化学计量特征及其对模拟氮沉降的响应

长白山苔原是我国乃至欧亚大陆东部独有的高山苔原,根据前人调查植被以灌木苔原为主要类型。在全球变暖背景下,近30年来,长白山岳桦林下的草本植物侵入苔原带,原生灌木苔原分化为灌木苔原、灌草苔原和草本苔原,形成了灌木、灌草混合和草本3种不同类型的凋落物,凋落物数量和质量发生显著改变。与此同时长白山苔原氮沉降量也在逐年增加,导致了土壤中氮的累积,势必影响凋落物的分解。凋落物作为连接植物和土壤的纽带,其分解过程中碳（C）、氮（N）、磷（P）等化学组分和化学计量比的变化直接和间接影响着土壤养分有效性和植物养分利用策略。为揭示氮沉降增加对长白山苔原带不同类型凋落物化学组分及生态化学计量特征早期变化的影响,开展了为期8个月的模拟氮沉降室内凋落物分解实验。在苔原带采集灌木优势种牛皮杜鹃和草本优势种小叶章的凋落物带回实验室,模拟灌木牛皮杜鹃群落、灌草混合的牛皮杜鹃-小叶章群落和草本小叶章群落的3种不同类型凋落物,设置三个施氮处理：对照（CK,0 g N m^-2 a^-1）、低氮（LN,10 g N m^-2 a^-1）、高氮（HN,20 g N m^-2 a^-1）。研究表明：（1）不施氮处理时,3种凋落物的C、P均呈释放状态,木质素（Li）呈先累积再略有降解趋势;牛皮杜鹃凋落物的N元素富集而其余两种凋落物N元素呈释放状态;灌草混合和草本凋落物比原生的灌木凋落物C和N元素释放快、Li累积少;而灌木凋落物的P释放略快于灌草和草本凋落物。3种植被类型凋落物的C/N、C/P、Li/N大小表现为：牛皮杜鹃凋落物>牛皮杜鹃-小叶章混生群落凋落物>小叶章凋落物;N/P表现为：小叶章凋落物>牛皮杜鹃凋落物>牛皮杜鹃-小叶章混生群落凋落物。（2）氮沉降促进3种类型凋落物分解过程中C、N和P化学组分的释放,且氮浓度越高促进作用越显著。在牛皮杜鹃凋落物分解过程中,氮素添加到达某一阈值后,其C/N、C/P、N/P、Li/N的降幅最大,后续若再增加氮素,其对化学计量比的影响均会减弱;本实验中的氮素添加量增加促进了小叶章凋落物的C/N、Li/N下降。（3）草本植物入侵引起凋落物类型的变化带来凋落物分解加快,将导致长白山苔原带养分循环的变化;氮沉降增加对小叶章凋落物化学组分的释放及C/N、Li/N的下降更为促进,小叶章凋落物内难分解化合物减少,分解受到促进。高氮沉降加快了小叶章凋落物与土壤、草本植物之间的养分循环。因此,随着未来苔原带氮沉降量的增加,将更有利于小叶章在与牛皮杜鹃的竞争中获胜,使苔原带呈现草甸化趋势。     

土地利用方式对滇池流域土壤养分时空分布的影响

选择滇池流域6种土地利用方式(废弃大棚区、林地、坡耕地、台地、平坝菜地和设施大棚菜地)逐月定点测定表层土壤pH以及氮、磷和有机质含量,分析土地利用方式对滇池流域土壤养分时空分布的影响.结果表明:研究区不同土地利用方式的土壤pH、有机质含量、总氮含量、总磷含量、C/N均存在显著差异.pH值依次为废弃大棚＞平坝菜地＞设施大棚＞台地＞坡耕地＞林地;有机质含量依次为废弃大棚＞平坝菜地＞设施大棚＞坡耕地＞林地＞台地;总氮含量依次为设施大棚＞平坝菜地＞废弃大棚＞坡耕地＞台地＞林地;总磷含量依次为平坝菜地＞设施大棚＞废弃大棚＞坡耕地＞台地＞林地;C/N值依次为林地＞坡耕地＞平坝菜地＞台地＞废弃大棚＞设施大棚.土壤中有机质、氮、磷含量受施肥、灌溉、田间耕作及季节因素等影响.不同样点各指标的高值均出现在雨季,可能与当地追肥习惯有关.各种土地利用方式下,土壤总氮、总磷和有机质含量之间呈显著正相关.高强度利用的设施大棚和废弃大棚的土壤pH以及氮、磷、有机质含量明显异于人为扰动较小的林地和台地.     

长期氮沉降下杉木人工林凋落物与土壤的C、N、P化学计量特征

为研究长期氮沉降条件下林木凋落物与土壤养分之间的关系,该文以亚热带杉木(Cunninghamia lanceolata)人工林为研究对象,分析了模拟氮沉降处理第12年时杉木林凋落物不同组分(叶、枝、果)与不同土层土壤(0～20 cm、20～40 cm、40～60 cm)的C、N、P含量及其化学计量比。氮沉降处理分4个水平,分别为N0(0 kg N·hm^-2·a^-1)、N1(60 kg N·hm^-2·a^-1)、N2(120 kg N·hm^-2·a^-1)、N3(240 kg N·hm^-2·a^-1),每处理重复3次。结果表明:(1)凋落物各组分的C、N、P含量及其化学计量比均高于土壤; 凋落物和土壤化学计量比均表现为C/P>C/N>N/P; 凋落物不同组分的C、N含量表现为叶>果>枝,而P含量表现为叶>枝>果。(2)12 a氮沉降增加了凋落物叶、枝和果的N含量,增幅分别为4.24%、15.97%、6.47%; 同时增加了凋落物枝N/P,降低了凋落物枝C含量、C/N和C/P; 中-高氮沉降(N2、N3)增加了土壤N含量,低氮沉降(N1)增加了土壤C/P、N/P。(3)相关性分析表明凋落物N与土壤N显著正相关,土壤C/P与凋落物C/P、N/P显著负相关,土壤P与凋落物N/P显著负相关。综上结果说明凋落物N是土壤N的重要N素来源之一,而土壤N可能是决定长期氮沉降后凋落物N/P的主要因素。     

农牧交错带不同土地利用类型土壤碳氮磷生态化学计量特征

为了阐明土地利用方式对土壤养分含量及土壤碳氮磷生态化学计量特征的影响,选择阴山北麓农牧交错带4种主要的土地利用类型(放牧草地、封育草地、弃耕地和耕地)为研究对象,分析了浅层土壤(0—25 cm)有机碳(SOC)、全氮(TN)、全磷(TP)、碱解氮(AN)和速效磷(AP)含量及土壤C、N、P生态化学计量特征。结果表明:1)研究区土壤贫瘠,养分含量整体水平不高,SOC、TN、TP含量分别为14.57、0.63、0.76 g/kg,AN和AP含量分别为39.87、6.72 mg/kg,5项养分指标均为中等变异。2)土地利用方式对土壤养分含量和土壤C、N、P生态化学计量特征均存在显著的影响,草地(封育草地、放牧草地)的SOC、TN和AN含量均高于农耕地(弃耕地、耕地),而TP和AP含量低于农耕地;草地的C∶N、C∶P和C∶P值均高于农耕地。3)土壤C、N、P元素化学计量值与C、N、P元素之间的最优拟合关系显示C∶N、C∶P主要受SOC影响,C∶P主要受N影响,表明SOC和N含量决定了研究区土壤中C、N、P化学计量特征的变化过程。研究结果对丰富土壤生态化学计量学科学理论具有重要意义,同时可为阴山北麓农牧交错带脆弱生态区的生态功能恢复提供科学依据。     

科尔沁沙地优势固沙灌木叶片氮磷化学计量内稳性

为科学认识科尔沁沙地优势固沙灌木的生态适应性和固沙植被演变规律, 该研究对科尔沁沙地流动沙丘、半固定沙丘、固定沙丘和丘间低地的优势固沙灌木小叶锦鸡儿(Caragana microphylla)和盐蒿(Artemisia halodendron)进行野外调查, 研究了这两种固沙灌木的叶片氮(N)、磷(P)化学计量特征、灌丛土壤养分状况以及内稳性特征。结果表明: 1)与盐蒿相比, 灌木小叶锦鸡儿具有较高的叶片N含量及N:P, 而P含量仅为盐蒿的1/2; 2)两种优势固沙灌木灌丛下土壤的全N、全P含量及速效N、速效P含量高于该地区土壤的平均水平, 小叶锦鸡儿灌丛下土壤养分含量显著高于盐蒿灌丛下土壤; 3)盐蒿叶片N、P化学计量内稳性指数(H)表现为H_P > H_N:P > H_N, 说明盐蒿更易受土壤N的限制; 小叶锦鸡儿叶片N、P化学计量内稳性指数表现为H_N:P > H_N > H_P, 意味着小叶锦鸡儿更易受土壤P的限制。在N含量较低的沙化草地, H_N较高的固沙灌木小叶锦鸡儿比盐蒿更具生长优势, 对于该地区生态恢复及保护具有不可替代的作用。然而, 小叶锦鸡儿额外吸收的N, 使其生长过程可能易受P的限制, 因此在沙地恢复过程中应注意土壤P的供应。     

泸沽湖流域土地利用方式对土壤肥力的影响

为探讨泸沽湖流域不同土地利用方式对土壤肥力的影响,采用野外调查、取样和室内分析相结合的方法,对泸沽湖流域内3种主要土地利用方式(农田、草地、林地)的土壤理化性状进行对比分析。结果表明:(1)土地利用类型对土壤肥力影响明显,农田含水率、全氮、速效氮、速效磷和速效钾含量相对较高;(2)林地有机质含量相对较高,草地全磷全钾含量相对较高;(3)土壤养分含量与土壤颗粒组成之间有一定的相关性,其中土壤全磷与砂粒呈显著正相关,土壤速效氮含量与粉粒呈显著负相关。     

血清IL-6、IL-8、IgM抗体及T细胞亚群水平对新生儿先天性梅毒的诊断价值

目的:探讨血清白介素-6(IL-6)、白介素-8(IL-8)、IgM抗体及T细胞亚群对先天性梅毒新生儿的诊断价值。方法:选择2015年5月至2017年5月在我院进行临床治疗的先天性梅毒新生儿81例为观察组,另选同期来我院进行健康体检81例新生儿为对照组。比较两组患者血清IL-6、IL-8、T细胞亚群中CD~(3+)、CD~(4+)、CD~(8+)、CD~(4+)/CD~(8+)细胞及IgM抗体的阳性率。结果:治疗后,观察组血清IL-6、IL-8水平均明显高于对照组(P0.05),T细胞亚群中CD~(3+)、CD~(4+)、CD~(4+)/CD~(8+)明显低于对照组,而CD~(8+)T细胞比例高于对照组(P0.05)。19S-IgM-TP ELISA法检测出IgM的阳性率92.59%,明显高于TRUST法(74.07%)及TP-ELSA法(70.37%)(P0.05)。ROC曲线中,血清IL-8特异度为88.34%明显高于血清IL-6特异度81.48%、IgM抗体特异度60.13%、T细胞亚群特异度65.34%;IgM抗体的曲线面积88.91 cm~2明显大于IL-6的曲线面积45.09 cm~2、IL-8的曲线面积76.19 cm~2、T细胞亚群的曲线面积77.35 cm~2;T细胞亚群准备性67.89%明显高于IL-6准确性60.39%、IL-8准确性51.09%、IgM抗体准确性50.12;IgM抗体的灵敏度60.13%高于IL-6灵敏度59.19%、IL-8灵敏度42.35%、T细胞亚群灵敏度59.37%。具有比较意义(P0.05)。结论:血清IL-6、IL-8水平、T细胞亚群中CD~(3+)、CD~(4+)、CD~(8+)、CD~(4+)/CD~(8+)及IgM抗体阳性率是诊断先天性梅毒新生儿的重要指标。     

Internal radiotherapy of painful bone metastases

Internal radiotherapy is effective in the treatment of metastatic bone pain and can improve quality of life. A number of controlled studies using various agents have shown a mean response rate in pain relief of 70–80% of treated patients. Some investigators prefer radionuclides which emit low beta particles for the treatment of bone pain, because the assumption of lower bone marrow toxicity of this agents. However, neither dosimetric data for radiation absorbed dose to the bone marrow nor clinical blood count depression have shown any significant differences between these agents. Other researchers suggest enhanced antitumoral effects using high-energy beta emitters and propose aggressive first-line treatment in the early disease stage instead of using these radiopharmaceuticals only in end-stage patients suffering intractable bone pain. Another approach consists of including other treatment modalities such as autologous stem cell rescue or in combination with chemo or bisphosphonate therapy to a radionuclide treatment scheme. Future research should focus more on the curative effects of combination with radiosensitizer, for example, chemotherapy, or repeated treatments with bone seeking agents.     

Specific 15N, NH correlations for residues in15 N, 13C and fractionally deuterated proteins that immediately follow methyl-containing amino acids

A triple-resonance pulse scheme is described which records¹⁵N, NH correlations of residues that immediately follow amethyl-containing amino acid. The experiment makes use of a¹⁵N, ¹³C and fractionally deuterated proteinsample and selects for CH₂D methyl types. The experiment isthus useful in the early stages of the sequential assignment process as wellas for the confirmation of backbone ¹⁵N, NH chemical shiftassignments at later stages of data analysis. A simple modification of thesequence also allows the measurement of methyl side-chain dynamics. This isparticularly useful for studying side-chain dynamic properties in partiallyunfolded and unfolded proteins where the resolution of aliphatic carbon andproton chemical shifts is limited compared to that of amide nitrogens.     

Retention of radionuclides by some aquatic fresh water plants

The uptake of radionuclides ⁶⁰Co, ³²P and ¹³⁴Cs by some aquatic plants (Lemna gibba, Ceratophyllum demersum and Potamogeton crispus) present in the Ismailia Canal at different pH values and for different contamination periods was studied. The experimental results showed that the uptake generally decreases as the water pH increased. The tested macrophytes proved to be reliable biological indicators.     

13C-31P Couplings in the Study of Conformational Properties of Some Diastereomeric Nucleoside-3′-Thiophosphate Derivatives

Synthesis and stereochemical characterization of enantiomerically pure nucleoside-3′-phosphorothioate esters and salts are reported. Vicinal carbon–phosphorus couplings reflect different predominance of the ? conformation in the isomeric (Rp and Sp) esters, while for the salts the ?^t conformation prevails in both stereoisomers. The influence of solvent and temperature on the conformational preferences is also described.     

Plutonium,241Am,90sr,and137cs concentrations in some antarctic matrices

A radioecological survey in Antarctica shows that the^239+240Pu,²³⁸Pu,²⁴¹Am,⁹⁰Sr, and¹³⁷Cs activities were detectable in nearly all the samples. The activity level of^239+240Pu,²⁴¹Am, and¹³⁷Cs in antarctic sediments was about 5–20 times lower than in the northern Adriatic Sea sediments, but the²³⁸Pu activities were relatively high. It was interesting to note that the⁹⁰Sr concentrations in all the sediments tended to be low, which could be the result of the easier exchangeable behavior of⁹⁰Sr in water. High concentrations were detected in mosses and lichens and their activity levels were comparable to those in central Italy. The radionuclide ratio analyses show that the major part of^239+240Pu,²⁴¹Am,⁹⁰Sr, and¹³⁷Cs was a result of nuclear weapon tests. The higher²⁴¹Am/^239+240Pu ratio was observed and it could perhaps be the result of fallout of nuclear weapon tests prior to 1962. The²³⁸Pu/^239+240Pu ratio in the antarctic matrices was about seven times higher than in the Northern hemisphere and it could be inferred that the major part of²³⁸Pu was originating from the SNAP-9A satellite accident.     

Microsampling of Fish Otoliths: A Comparison Between DM 2800 and Dremel in Stable Isotope Analysis

This paper describes and compares two microsampling methods, DM 2800 and Dremel, which were used in taking aragonite samples from otolith zones of cod, Gadus morhua, for stable isotope analysis. There were no significant differences between the two sampling methods both in carbon and oxygen isotope ratios (¹³C/¹²C, ¹⁸O/¹⁶O) and in annual and seasonal otolith zones. The possible finite effect with Dremel could be minimized or negligible by selecting otoliths of younger fishes. Thus, Dremel may be accepted as a convenient microsampling method in stable isotope analysis of otoliths.     

Ischemic changes in myocardial ionic contents of the isolated perfused rat hearts as studied by NMR

Using³¹P-,²³Na- and³⁹K-NMR, we assessed ischemic changes in high energy phosphates and ion contents of isolated perfused rat hearts continuously and systematically. To discriminate intra- and extracellular Na⁺, a shift reagent (Dy(TTHA)^3–) was used in²³Na-NMR study. In³⁹K-NMR study, the extracellular K⁺ signal was suppressed by inversion recovery pulse sequence in order to obtain intracellular K⁺ signal without using shift reagnets. During the early period of ischemia, increases in intracellular Na⁺ and inorganic phosphate (Pi) were observed in addition to the well-documented decreases in creatine phosphate and ATP and a fall of intracellular pH, suggesting an augmented operation of Na⁺–H⁺ exchange triggered by a fall of the intracellular pH resulted from breakdown of ATP. At around 15 min of ischemia, a second larger increase in intracellular Na⁺ and a decrease in intracellular K⁺ were observed in association with a second increase in Pi. This was accompnanied by an abrupt rise of the ventricular end-diastolic pressure. As there was a depletion of ATP at this time, the increase in intracellular Na⁺ and associated decrease in intracellular K⁺ may be explained by inhibition of the Na⁺–K⁺ ATPase due to the depletion of ATP. A longer observation with³¹P-NMR revealed a second phosphate peak (at lower magnetic field to ordinary Pi peak) which increased its intensity as ischemic time lengthened. The pH of this 2nd peak changed in parallel with the changes in pH of the bathing solution, indicating the appearance of a compartment whose hydrogen concentration is in equilibrium with that of the external compartment. Thus, the peak could be used as an index of irreversible membrane damage of the myocardium.     

HNCAN pulse sequences for sequential backbone resonance assignment across proline residues in perdeuterated proteins

A TROSY-based triple-resonance pulse scheme is described which correlates backbone ¹H and ¹⁵N chemical shifts of an amino acid residue with the ¹⁵N chemical shifts of both the sequentially preceding and following residues. The sequence employs ¹ J _NC and ² J _NC couplings in two sequential magnetization transfer steps in an `out-and-back' manner. As a result, N,N connectivities are obtained irrespective of whether the neighbouring amide nitrogens are protonated or not, which makes the experiment suitable for the assignment of proline resonances. Two different three-dimensional variants of the pulse sequence are presented which differ in sensitivity and resolution to be achieved in one of the nitrogen dimensions. The new method is demonstrated with two uniformly ²H/¹³C/¹⁵N-labelled proteins in the 30-kDa range.     

Palytoxin Acts on Na+,K+-ATPase but not Nongastric H+,K+-ATPase

Palytoxin (PTX) opens a pathway for ions to pass through Na,K-ATPase. We investigate here whether PTX also acts on nongastric H,K-ATPases. The following combinations of cRNA were expressed in Xenopus laevis oocytes: Bufo marinus bladder H,K-ATPase α₂- and Na,K-ATPase β₂-subunits; Bufo Na,K-ATPase α₁- and Na,K-ATPase β₂-subunits; and Bufo Na,K-ATPase β₂-subunit alone. The response to PTX was measured after blocking endogenous Xenopus Na,K-ATPase with 10 μm ouabain. Functional expression was confirmed by measuring ⁸⁶Rb uptake. PTX (5 nm) produced a large increase of membrane conductance in oocytes expressing Bufo Na,K-ATPase, but no significant increase occurred in oocytes expressing Bufo H,K-ATPase or in those injected with Bufo β₂-subunit alone. Expression of the following combinations of cDNA was investigated in HeLa cells: rat colonic H,K-ATPase α₁-subunit and Na,K-ATPase β₁-subunit; rat Na,K-ATPase α₂-subunit and Na,K-ATPase β₂-subunit; and rat Na,K-ATPase β₁- or Na,K-ATPase β₂-subunit alone. Measurement of increases in ⁸⁶Rb uptake confirmed that both rat Na,K and H,K pumps were functional in HeLa cells expressing rat colonic HKα₁/NKβ₁ and NKα₂/NKβ₂. Whole-cell patch-clamp measurements in HeLa cells expressing rat colonic HKα₁/NKβ₁ exposed to 100 nm PTX showed no significant increase of membrane current, and there was no membrane conductance increase in HeLa cells transfected with rat NKβ₁- or rat NKβ₂-subunit alone. However, in HeLa cells expressing rat NKα₂/NKβ₂, outward current was observed after pump activation by 20 mm K⁺ and a large membrane conductance increase occurred after 100 nm PTX. We conclude that nongastric H,K-ATPases are not sensitive to PTX when expressed in these cells, whereas PTX does act on Na,K-ATPase.