异丙嗪对家兔EGTA性发热的解热作用及其机制研究

目的：观察异丙嗪（ｐｒｏｍｅｔｈａｚｉｎｅ,ＰＭＺ）对家兔ＥＧＴＡ性发热的影响并探讨其作用机制。方法：侧脑室和静脉给药。用Ｆｕｒａ－２荧光分光光度法测定细胞内游离钙浓度（［Ｃａ２＋］ｉ）。结果：（１）侧脑室灌注０６μｍｏｌＥＧＴＡ引起家兔明显的发热反应,侧脑室灌注０６μｍｏｌＥＧＴＡ２０ｍｉｎ后,静脉注射ＰＭＺ（５ｍｇ／ｋｇ）明显抑制ＥＧＴＡ引起的结肠温度上升,其３ｈ发热反应指数明显低于侧脑室灌注０６μｍｏｌＥＧＴＡ２０ｍｉｎ后静脉注射生理盐水（ＮＳ）组。而侧脑室灌注人工脑脊液（ＡＣＳＦ）２０ｍｉｎ后静脉注射ＰＭＺ（５ｍｇ／ｋｇ）组家兔结肠温度明显低于ＡＣＳＦ＋ＮＳ对照组。（２）体外实验发现,向下丘脑细胞悬液中加入终浓度为０７４ｍｍｏｌ／Ｌ的ＰＭＺ,下丘脑细胞［Ｃａ２＋］ｉ从（１５９２±１８８）ｎｍｏｌ／Ｌ升高到（５３３７±９０１）ｎｍｏｌ／Ｌ（Ｐ＜００５）。结论：ＰＭＺ诱导体温调节中枢神经细胞［Ｃａ２＋］ｉ升高可能是ＰＭＺ抑制家兔ＥＧＴＡ性发热的中枢机制之一。     

尼可地尔降低血管平滑肌细胞内ATP诱导的游离钙浓度

目的：探讨尼可地尔对血管平滑肌细胞内游离钙（［Ｃａ２＋］ｉ）的影响及机理。方法：培养的兔主动脉平滑肌细胞加入Ｆｕｒａ－２ＡＭ２５μｍｏｌ／Ｌ,在３７℃下孵育５０ｍｉｎ,［Ｃａ２＋］ｉ用荧光分光光度计检测。结果：ＡＴＰ（０１ｍｍｏｌ／Ｌ）诱导的［Ｃａ２＋］ｉ峰相和持续相增加可被尼可地尔抑制,且呈剂量依赖性,尼可地尔（１０μｍｏｌ／Ｌ）的抑制作用可被优降糖（１０μｍｏｌ／Ｌ）完全阻断（峰相：５３０±３１ｖｓ５４４±４１ｎｍｏｌ／Ｌ,持续相：３７０±１９ｖｓ３８１±１１ｎｍｏｌ／Ｌ,Ｐ＞００５）;在无钙溶液中,先给尼可地尔能显著抑制ＡＴＰ诱导的［Ｃａ２＋］ｉ峰相增加。结论：尼可地尔抑制ＡＴＰ诱导的［Ｃａ２＋］ｉ增加,可能与减少细胞外钙内流及细胞内钙释放有关。     

内皮素对成年鼠离体心室肌细胞内游离钙浓度的影响及机制

目的和方法：采用分离的Ｓｐｒａｇｕｅ－Ｄａｗｌｅｙ大鼠心室肌细胞,以Ｆｕｒａ－２／ＡＭ荧光指示剂负载,检测心肌细胞内游离钙浓度（［Ｃａ２＋］ｉ）变化,探讨内皮素－１（ＥＴ－１）对［Ｃａ２＋］ｉ的作用及其机制。结果：ＥＴ－１（１×１０－７ｍｏｌ／Ｌ）引起［Ｃａ２＋］ｉ升高分两个时相：快速相和持续相,可被ＥＴＡ的特异性受体阻断剂ＢＱ１２３（２×１０－６ｍｏｌ／Ｌ）所阻断。移去细胞外液钙以及用百日咳毒素（２００ｎｇ／ｍＬ）处理１０ｈ后,ＥＴ－１仍引起快速相,但持续相消失。Ｒｙａｎｏｄｉｎｅ（４μｍｏｌ／Ｌ）和异搏定（２×１０－５ｍｏｌ／Ｌ）对ＥＴ－１诱导［Ｃａ２＋］ｉ升高的作用无显著影响。结论：ＥＴ－１升高［Ｃａ２＋］ｉ是通过ＥＴＡ受体介导;快速相［Ｃａ２＋］ｉ升高主要由胞内Ｒｙａｎｏｄｉｎｅ不敏感的钙池释放造成,与百日咳毒素敏感的Ｇ蛋白无关;持续相［Ｃａ２＋］ｉ升高主要由胞外Ｃａ２＋内流引起,不是通过电压依赖性Ｌ－型钙通道介导,与百日咳毒素敏感的Ｇ蛋白有关     

大鼠心房特殊颗粒Ca^2＋—ATP酶特性的研究

本实验对心房特殊颗粒（ＡＳＧ）膜上Ｃａ＾２＋－ＡＴＰ酶的特性进行研究，并与肌浆网（ＳＲ）膜上的Ｃａ＾２＋－ＡＴＰ酶特性进行比较。在１０ｍｍｏｌ／Ｌ Ｃａ＾２＋溶液中，二者膜上均显示酶活性，酶活性在１ｍｍｏｌ／Ｌ Ｃａ＾２＋孵育液中均减弱，并在Ｃａ＾２＋浓度降至０．１ｍｍｏｌ／Ｌ时酶反应均不显示。在加入０．１ｍｍｏｌ／Ｌ槲皮黄酮后，ＳＲ和ＡＳＧ膜上的酶活性同时被抑制；当加入０．１ｍｍｏｌ／Ｌ寡霉素后     

去甲肾上腺素对大鼠腹腔巨噬细胞内IP_3、［Ca~（2＋）］_i和Ia抗原表达

本文应用细胞膜放射标记和离子交换层析法测定巨噬细胞（ＭФ）内肌醇－１，４，５－三磷酸（ＩＰ３）、用Ｃａ￣（２＋）指示剂的分光光谱法测定ＭФ内Ｃａ￣（２＋）浓度（［Ｃａ￣（２＋）］）、用ＡＰＡＡＰ桥联酶标法检测ＭФ表面Ｉａ抗原的表达，研究去甲肾上腺素（ＮＥ）对大鼠腹腔的ＭФ内ＩＰ３、［Ｃａ￣（２＋）］ｉ和ＭФ表面ｌａ抗原表达的影响。结果显示ＮＥ（１０￣（－８）ｍｏｌ／Ｌ）可显著增高ＭФ中ＩＰ＿３含量（４４２±２２ｃｐｍ／１０￣６ｃｅｌｌｓ，对照组１０２±８ｃｐｍ／１０￣６ｃｅｌｌｓ，Ｐ＜０．０１）；ＮＥ可使ＭФ内［Ｃａ￣（２＋）］ｉ显著增高（３２２±７８ｎｍｏｌ／Ｌ，对照组９７±１７ｎｍｏｌ／Ｌ，Ｐ＜０．０１）；ＮＥ可显著增高ＭФ表面Ｉ－Ａ、Ｉ－Ｅ抗原的表达（６４±８％、５８±６％，对照组５０±３％，４４±４％，Ｐ＜０．０１）。提示神经递质ＮＥ促进ＭФ表面Ｉａ抗原表达的作用可能是通过第二信使ＩＰ＿３和Ｃａ￣（２＋）介导的。     

SRBC膜提取物对猪PBMNC第二信使的影响

胰酶水解绵羊红细胞（ＳＲＢＣ）释放膜表面活性蛋白组分Ⅲ（ＴＲＦ－Ⅲ），单独作用可使猪外周血单个核细胞（ＰＢＭＮＣ）胞内ｃＡＭＰ水平升高，以１００μｇ／ｍｌ浓度刺激达最高峰，由对照组０．９４±０．１４ｐｍｏｌ／Ｌ升高到２．７５±０．２５ｐｍｏｌ／Ｌ（Ｐ＜０．０１）。如果ＰＢＭＮＣ事先与腺苷酸环化酶（ＡＣａｓｅ）抑制剂ＬｉC１孵育后再以ＴＲＦ－Ⅲ或ＰＡＨ刺激。ｃＡＭＰ增高受到抑制（Ｐ＜０．０１）；而ＥＤＴＡ－２Ｎａ（一种磷酸二酯酶ＰＤＥ抑制剂）对此ｃＡＭＰ升高无影响。结果提示，此ｃＡＭＰ升高主要是通过活化ＡＣａｓｅ水解ＡＴＰ生成ｃＡＭＰ，而不像是抑制ＰＤＥ减少ｃＡＭＰ降解引起的。ＴＲＦ－Ⅲ诱导猪ＰＢＭＮＣ胞内Ｃａ~(２＋)浓度升高，以１００μｇ／ｍｌ刺激２分钟升高最多，由对照组的２４２±７ｎｍｏｌ／Ｌ升高到３２３±１５ｎｍｏｌ／Ｌ（Ｐ＜０．０１）。以ＥＧ－ＴＡ除去胞外Ｃａ~(２＋)再以ＴＲＦ－Ⅲ或ＰＡＨ刺激，仅观察到小范围［Ｃａ~(２＋)］ｉ升高。看来这一过程包括了刺激胞内Ｃａ~(２＋)释放和胞外Ｃａ~(２＋)内流两种方式。以上结果证明，ＴＲＦ－Ⅲ对淋巴细胞功能影响与细胞内第二信使有关。     

咖啡因对胎鼠及乳鼠睾丸生殖细胞DNA合成影响的体外研究

目的：了解咖啡因对胚胎及新生时期生殖细胞合成ＤＮＡ的影响及其机制。方法：采用低（０３ｍｍｏｌ／Ｌ）、中（０６ｍｍｏｌ／Ｌ）、高（１２ｍｍｏｌ／Ｌ）浓度咖啡因体外培养ＳＤ孕１８ｄ胎鼠、０ｄ及４ｄ乳鼠睾丸组织块,培养时间分别为１、２、３周,用放射自显影、计算机图像分析的方法观察咖啡因对生殖细胞摄取［３Ｈ］－ＴｄＲ及ＤＮＡ含量的影响。结果：（１）１８ｄ胎鼠、０ｄ乳鼠、４ｄ乳鼠睾丸培养组织内生殖细胞受咖啡因影响依次增加。（２）浓度越高、培养时间越长,咖啡因对生殖细胞影响越明显。（３）生殖细胞数量的减少往往伴随ＤＮＡ含量和［３Ｈ］－ＴｄＲ摄取的降低。结论：高浓度咖啡因长时间培养后使生殖细胞数量减少可能与干扰细胞摄取ＤＮＡ前体物质,降低细胞内ＤＮＡ含量有关。     

下丘脑[Ca^2＋]i,cAMP在家兔EGTA性发热机制中的作用

用６０只新西兰兔分两部分进行实验。（１）用１２只制备下丘脑细胞悬液，在离体条件下，应用Ｆｕｒａ－２荧光指示剂测定细胞内Ｃａ＾２＋浓度（Ｃａ＾２＋］ｉ）。结果表明，用ＥＧＴＡ络合神经细胞外Ｃａ＾２＋而降低细胞外Ｃａ＾２＋浓度时，下丘脑神经细胞（［Ｃａ＾２＋］ｉ）明显降低（Ｐ＞０．０１）；相反，增加细胞外Ｃａ＾２＋浓度，则［Ｃａ＾２＋］ｉ明显增高（Ｐ＞０．０１）。（２）用４８只家兔分４组，分别向侧脑室     

乙酰胆碱对大鼠腹腔巨噬细胞内钙离子浓度和表面Ia抗原表达的影响

用Ｆｕｒａ－２作为荧光探针测定大鼠腹腔巨噬细胞（Ｍ）内钙离子浓度（［Ｃａ￣（２＋）］ｉ），ＡＰＡＡＰ桥联酶标法检测Ｍ表面Ｉａ抗原的表达。结果表明：５×１０￣（－６）ｍｏｌ／Ｌ的乙酞胆碱（Ａｃｈ）可使Ｍ［Ｃａ￣（２＋）］ｉ；明显上升，可促进Ｍ表面Ｉ－Ａ和Ｉ－Ｅ抗原的表达，而阿托品（１０￣（－５）ｍｏｌ／Ｌ）可阻断Ａｃｈ升高［Ｃａ￣（２＋）］ｉ的作用。阿托品、三氟啦嚎（ＴＦＰ，５０μｍｏｌ／Ｌ）、ＥＧＴＡ（６ｍｍｏｌ／Ｌ）均可阻断Ｍ促进ＭＩａ抗原表达的作用，ｃＡＭＰ依赖性蛋白激酶抑制剂（ＰＫＩ，２５μｇ／ｍｌ）对Ａｃｈ促进ＭＩａ抗原表达的作用无影响。     

粘附分子对CD3介导的胸腺细胞[Ca^2＋]i应答的影响

ＬＦＡ－１和ＩＣＡＭ－１广泛表达于各胸腺细胞亚群，但ＩＣＡＭ－１在ＰＮＡ￣＋细胞的表达下调。本文报道：用抗ＬＦＡ－１／ＩＣＡＭ－１和抗ＣＤ３单抗，分析了粘附分子ＬＦＡ－１／ＩＣＡＭ－１对抗ＣＤ３诱导的胸腺细胞［Ｃａ￣（２＋）］ｉ应答的影响。结果显示，可溶性抗ＬＦＡ－１／ＩＣＡＭ－１可抑制ＣｏｎＡ刺激的胸腺细胞增殖，且以抗ＬＦＡ－１抗体的作用更为显著，在ＣｏｎＡ或抗ＣＤ３诱导的胸腺细胞［Ｃａ￣（２＋）］ｉ应答中，抗ＬＦＡ－１单抗可明显抑制［Ｃａ￣（２＋）ｉ升高。但如果用二抗交联ＣＤ３和ＬＦＡ－１，胸腺细胞［Ｃａ￣（２＋）ｉ则显著高于单独交联ＣＤ３时的水平（Ｐ＜０．０１），而ＣＤ３与ＩＣＡＭ－ｌ交联却无此效应，此外，仅交联ＬＦＡ－１或ＩＣＡＭ－１也无诱导［Ｃａ￣（２＋）］ｉ应答的作用。提示在ＬＦＡ－ｌ与ＩＣＡＭ－１介导的胸腺细胞与胸腺基质细胞相互作用中，ＬＦＡ－１可为ＴＣＲ／ＣＤ３途径介导的胸腺细胞活化提供复合刺激信号。     

Auxin influx carriers stabilize phyllotactic patterning

One of the most striking features of plant architecture is the regular arrangement of leaves and flowers around the stem, known as phyllotaxis. Peaks in concentration of the plant hormone auxin, generated by the polar localization of the PIN1 auxin efflux carrier, provide the instructive signal for primordium initiation. This mechanism generates the spacing between neighboring primordia, which results in regular phyllotaxis. Studies of the role of auxin transport in phyllotactic patterning have focused on PIN1-mediated efflux. Recent computer simulations indicate an additional role for transporter-mediated auxin uptake. Mutations in the AUX1 auxin influx carrier have not, however, been reported to cause an aerial phenotype. Here, we study the role of AUX1 and its paralogs LAX1, LAX2, and LAX3. Analysis of the quadruple mutant reveals irregular divergence angles between successive primordia. A highly unusual aspect of the phenotype is the occurrence of clusters of primordia, in violation of classical theory. At the molecular level, the sharp peaks in auxin levels and coordinated PIN polarization are reduced or lost. In addition, the increased penetrance of the phenotype under short-day conditions suggests that the AUX LAX transporters act to buffer the PIN-mediated patterning mechanism against environmental or developmental influences.     

Calcium influx pathways in rat pancreatic ducts

A number of agonists increase intracellular Ca²⁺ activity, [Ca²⁺]_i, in pancreatic ducts, but the influx/efflux pathways and intracellular Ca²⁺ stores in this epithelium are unknown. The aim of the present study was to characterise the Ca²⁺ influx pathways, especially their pH sensitivity, in native pancreatic ducts stimulated by ATP and carbachol, CCH. Under control conditions both agonists led to similar changes in [Ca²⁺]_i. However, these Ca²⁺ transients, consisting of peak and plateau phases, showed different sensitivities to various experimental manoeuvres. In extracellular Ca²⁺-free solutions, the ATP-induced [Ca²⁺]_i peak decreased by 25%, but the CCH-induced peak was unaffected; both plateaus were inhibited by 90%. Flufenamate inhibited the ATP-induced peak by 35%, but not the CCH-evoked peak; the plateaus were inhibited by 75–80%. La³⁺ inhibited the ATP-induced plateau fully, but that induced by CCH by 55%. In resting ducts, an increase in extracellular pH, pH_e, by means of HEPES and HCO₃ ⁻/CO₂ buffers, increased [Ca²⁺]_i; a decrease in pH_e had the opposite effect. In stimulated ducts the pH-evoked effects on Ca²⁺ influx were more pronounced and depended on the agonist used. At pH_e 6.5 both ATP- and CCH-evoked plateaus were inhibited by about 50%. At pH 8.0 the ATP-stimulated plateau was inhibited by 27%, but that stimulated by CCH was increased by 72%. Taken together, we show that CCH stimulates Ca²⁺ release followed by Ca²⁺ influx that is moderately sensitive to flufenamate, La³⁺, depolarisation, it is inhibited by low pH, but stimulated by high pH. ATP stimulates Ca²⁺ release and probably an early Ca²⁺ influx, which is more markedly sensitive to flufenamate and La³⁺, and is both inhibited by low and high pH. Thus our study indicates that there are at least two separate Ca²⁺ influx pathways in pancreatic ducts cells. Received: 4 December 1995/Received after revision and accepted: 1 February 1996     

Neutrophil leukocyte motility requires directed water influx

The ability of neutrophils to sense and move to sites of infection is essential for our defense against pathogens. For motility, lamellipodium extension and stabilization are prerequisites, but how cells form such membrane protrusions is still obscure. Using contrast-enhanced video microscopy and Transwell assays, we show that water-selective aquaporin channels regulate lamellipodium formation and neutrophil motility. Addition of anti-aquaporin-9 antibodies, HgCl(2), or tetraethyl ammonium inhibited the function(s) of the channels and blocked motility-related shape changes. On human neutrophils, aquaporin-9 preferentially localized to the cell edges, where N-formyl peptide receptors also accumulated, as assessed with fluorescence microscopy. To directly visualize water fluxes at cell edges, cells were loaded with high dilution-sensitive, self-quenching concentrations of fluorophore. In these cells, motile regions always displayed increased fluorescence compared with perinuclear regions. Our observations provide the first experimental support for motility models where water fluxes play a pivotal role in cell-volume increases accompanying membrane extensions.     

Cytoplasmic calcium oscillations and store-operated calcium influx

Intracellular calcium oscillations have fascinated scientists for decades. They provide an important cellular signal which, unlike most signalling mechanisms, is digitally encoded. While it is generally agreed that oscillations most frequently arise from cyclical release and re-uptake of intracellularly stored calcium, it is becoming increasingly clear that influx of calcium across the plasma membrane also plays a critical role in their maintenance and even in delivering their signal to the correct cellular locus. In this review we will discuss the role played by Ca²⁺ entry mechanisms in Ca²⁺ oscillations, and approaches to understanding the molecular nature of this Ca²⁺ entry pathway.     

Prostaglandins induce calcium influx in human spermatozoa

Progesterone, prostaglandin and follicular fluid are reported to enhance the acrosome reaction through the influx of extracellular calcium into the cytoplasm of human spermatozoa. Prostaglandins are present within the male reproductive tract, and high concentrations of prostaglandins exist in seminal fluid. In order to investigate the mechanisms by which prostaglandins enhance the acrosome reaction through calcium influx, the intracellular calcium response induced by progesterone, prostaglandin E1 (PGE1), prostaglandin E2 (PGE2) and follicular fluid was measured using fura-2. PGE1 and PGE2 promoted calcium influx dose dependently through dihydropyridine insensitive calcium channels. Refractoriness of the elevation of intracellular Ca2+ concentration ([Ca2+]i) to a second stimulus occurred when 60 microg/ml PGE1 was administered 100 s after the prior administration of 60 microg/ml of PGE1, and similarly when 1 microg/ml of progesterone was administered 100 s after the prior administration of 1 microg/ml of progesterone. Refractoriness also occurred when 60 microg/ml PGE1 was administered after the prior addition of 60 microg/ml PGE2, but did not occur between PGE1 and progesterone. Pertussis toxin (PTX) did not modify the changes in [Ca2+]i after the addition of PGE1 or PGE2. In conclusion, PGE1 and PGE2 promoted calcium influx through PTX- insensitive calcium channels which appeared to be recognized by a common receptor different from that of progesterone.      

The influx of orthophosphate into squid giant axons

1. The influx of (32)P, applied externally as orthophosphate, into the axoplasm of squid giant axons has been studied.2. An average orthophosphate influx of 20.9 f-mole/cm(2).sec is obtained if the (32)P found in the axoplasm is assumed to be indicative of orthophosphate which has crossed the axolemma.3. The influx does not show very much dependence on external orthophosphate concentration in the range 0.02-0.5 mM.4. The influx is reduced by cyanide, 2,4-dinitrophenol, ouabain and by the absence of external potassium.5. The (32)P appears to arrive in the axoplasm as orthophosphate.6. It is concluded that there is an inward movement of orthophosphate into the axons which is mediated by an active transport process and that this may have some connexion with the active transport of sodium and potassium.     

Ca2+ influx and platelet membrane glycoproteins

When aequorin-loaded platelets were stimulated with thrombin, the luminescence of aequorin showed two peaks. From experiments with 1 mM external Ca2+ or 1 mM EGTA, both one-half of the first peak and the entire second peak reflected the influx of Ca2+ from the external medium, and the remaining half of the first peak reflected the mobilization of Ca2+ from its storage site. A monoclonal antibody (TM83), that recognizes the GPIIb/IIIa complex which has binding sites for fibrinogen, and synthetic peptide GRGDSP are known to inhibit fibrinogen binding and platelet aggregation. Both of them eliminated the second peak of intracellular free calcium. Similar effects were observed during activation by collagen, but not by TPA. Also dihydrocytochalasin B inhibited the second peak of Ca2+ influx by thrombin, suggesting that the signal, which was caused by fibrinogen-binding to GPIIb/IIIa (aggregation) in thrombin-activated platelets, is transferred to the inner sites of GPIIb/IIIa complex and induces the cytoskeletal reorganization such as actin polymerization. This in turn, induces the secondary increase in [Ca2+] i of platelets. It is interesting that ticlopidine inhibited the Ca2+ influx through the GPIIb/IIIa complex. This result suggests the importance of such kinds of antiplatelet drugs to prevent thrombus formation.     

Sodium-dependent influx of orthophosphate in mammalian non-myelinated nerve.

1. The rate of uptake of radiophosphate was measured in desheathed vagus nerves of rabbits mounted in an apparatus where the incubating solution flowed along the preparation. 2. Replacement of the Na of the Locke by either choline or Tris slowed the rate of uptake to about 10% of its value in Na; with K it was slowed to 20%; and with Li to 50%. 3. Measurements of the rate of uptake at different extracellular phosphate concentrations showed that in choline-Locke the influx of phosphate was proportional to the extracellular phosphate concentration, while in Locke the rate of inward flow showed a tendency to saturation with increasing phosphate concentrations. 4. Extracts of nerves after 45 min exposure to labelled solutions showed for different phosphate concentrations a slowing of the labelling of ATP, ADP and creatine-phosphate (CrP) and inorganic phosphate (Pi) when Locke was replaced by choline-Locke. 5. A similar slowing was found when, at 0-2 mM phosphate, the labelling of these compounds was measured at different times: application of choline-Locke reduced the rate of incorporation of 32P to about 15% of the rate in Locke. 6. In preparations that were loaded with radiophosphate and then washed with inactive solution, and the effluent fractionated, over 90% of the radioactivity was found in the inorganic phosphate fraction. 7. The efflux of 32P showed an initial exponential phase with a time constant of 20-30 min and a much slower one. The slow efflux had a rate constant of 0-0014 min-1 in 0-2 mM external phosphate. 8. Increasing the external phosphate concentration increased the efflux. 9. Prolonged incubation in choline-Locke reduced the efflux. 10. The influx of phosphate was calculated for different external phosphate concentrations using the rate of uptake of radiophosphate measured 45 min after the application of isotope and the corresponding efflux rate coefficient and the intracellular specific activities of the labelled compounds. 11. A correction was also introduced for diffusion, using the "limited biophase model". 12. The Na-sensitive influx, i.e. the difference between influx in Locke and influx in choline-Locke, showed saturation kinetics. 13. A Lineweaver-Burk plot for Na-sensitive uncorrected influxes gave a vmax of 16-7 mumole/kg wet wt. min and an apparent Km of 0-42 mM; for the corrected fluxes these values were 18-2 and 0-36. 14. It is concluded that a large part of phosphate influx and some of the phosphate efflux is mediated by a specific Na-dependent phosphate transport system. 15. This system seems to be present also in other types of nervous tissues and probably in many types of animal cells.