Hiroaki Furuya

The Effect of EGF on Electrolyte Transport Is Mediated by Tyrosine Kinases in the Rabbit Cortical Collecting Duct

Epidermal growth factor (EGF) inhibits amiloride-sensitive Na+ conductance in the apical membrane of the isolated rabbit cortical collecting duct. However, there is no information on the relationship between electrolyte transport and tyrosine kinase. We examined the effect of EGF on transport of potassium and chloride as well as sodium and the roles of tyrosine kinases in the rabbit cortical collecting duct using in vitro isolated tubular microperfusion. Basolateral EGF depolarized the transepithelial voltage in a dose-dependent manner within a concentration range of 10−10 in 10−8 M. Basolateral ouabain and luminal amiloride completely abolished EGF-induced depolarization. However, luminal BaCl2 did not abolish its depolarization. To confirm the mechanism, sodium, potassium, and chloride fluxes were measured in the presence of 10−10M EGF. EGF significantly decreased the lumen-to-bath isotope flux of sodium and chloride from 93.6±12.5 to 61.1±9.6 pmol/mm/min (n = 5, p<0.05) and from 86.6±10.0 to 54.8±9.7 pmol/mm/min (n = 10, p<0.01), respectively. EGF also decreased net potassium secretion from −27.7±5.9 to –7.8±1.5 pmol/mm/min (n = 6, p<0.01). To examine whether EGF-induced depolarization is mediated by tyrosine kinase, tyrosine kinase inhibitors were applied from the basolateral side. Pretreatment with 1 µg/ml herbimycin A for 120 min completely abolished EGF-induced depolarization (90.9±5.4%, n = 4; NS). Herbimycin A itself also did not change the lumen-to-bath isotope flux of sodium and completely abolished the inhibition of Na+ absorption on EGF action (control 65.4±6.8, herbimycin A 61.8±6.3, EGF with herbimycin A 60.0±4.4 pmol/min/mm, n = 5; NS). In conclusion, EGF depolarizes transepithelial voltage by inhibiting sodium transport primarily and potassium and chloride transport secondarily. These effects were blocked by nonspecific tyrosine kinase inhibitors.

A New Device to Monitor Blood Volume in Hemodialysis Patients

We developed a new optical device (Nikkiso) to assess changes through blood volume monitoring (BVM) during hemodialysis and were able to determine the ideal levels in which changes in blood volume percentage (BV%) occur among hemodialysis patients in one hemodialysis center. We evaluated both the reliability of BVM and these ideal levels in a multicenter group. The purpose of this manuscript is to develop a navigating system to set dry weight in a variety of situations as the final goal. First, based on the obtained BVM (BV%BVM) measurements, the relationships between BV% and hematocrit (BV%HT) and between BV% and CRIT‐LINE (BV%CLM; Hema Metrics, Kaysville, UT, USA) were then evaluated. In 30 hemodialysis patients, there was a close correlation between both BV%BVM vs. BV%HT and BV%BVM vs. BV%CLM (n = 30, r = 0.967, P < 0.001, and n = 36, r = 0.7867, P < 0.001, respectively). Second, BV% data were obtained from 464 treatment cases performed on 26 subjects in one satellite hemodialysis center on patients whose body weight was deemed clinically suitable. The formulas for the levels of BV% (standardized by the percent change in body weight at the end of hemodialysis treatment: BW%end) were determined.

Effect of ticlopidine hydrochloride on erythropoietin-induced rise in blood pressure in patients on maintenance hemodialysis.

Background/Aims: A recent observation that antiplatelet-aggregation drugs, including ticlopidine hydrochloride, may prevent erythropoietin (EPO)-induced rise in blood pressure in hemodialysis (HD) patients remains a subject of particular interest. The aim of the present study was to determine the effect of ticlopidine hydrochloride on EPO-induced rise in blood pressure of HD patients with special reference to blood levels of vasoactive substances. Methods: HD patients who showed hypertension or aggravation of preceding hypertension with EPO treatment were selected for this study. Ticlopidine hydrochloride was administered at a dose of 200 mg daily for 4 weeks. Blood pressure and serum levels of nitric oxide (NO), atrial natriuretic peptide (ANP) and endothelin (ET) were determined before and after drug administration. Patients were divided into two groups, one of which showed a drop in mean blood pressure (MBP) of >10 mm Hg (group I) and one which did not (group II), and a comparison was made between them with respect to the blood parameters. Results: Five of 15 patients showed a drop of MBP of >10 mm Hg (group I), and 10 patients did not show any change in MBP (group II). In group I, there was a significant increase in blood NO levels compared to the concentrations before ticlopidine administration, while there was no change in group II. With respect to ANP and ET, there was no significant change in either of the groups. Conclusion: The findings suggest that the preventive effect of ticlopidine hydrochloride on EPO-induced rise in blood pressure may partly be related to the enhancement of NO production in patients on maintenance HD.

Intracellular alkalosis stimulates potassium secretion in rabbit CCD

AbstractBackground. Clinically, it is well known that alkalosis induces hypokdemia, but the precise mechanisms of these interactions between acid-base disturbances and potassium homeostasis are not known with certainty. The role of intracellular alkalosis in the regulation of transepithelial potassium transport was examined in rabbit cortical collecting ducts (CCD). Methods. Intracellular alkalosis was induced by 25 mM N-2 hydroxyethylpiperazine-N′-2-ethanesulfonic acid (HEPES) buffer in which bicarbonate and CO2 were eliminated. Intracellular pH (pHi) was measured by the load of 2′,7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF) dye in principal cells. Isolated CCD was perfused in vitro, and electrophysiological studies and electrolyte transport studies were performed with or without HEPES buffer. Results. Basal pHi in the Krebs-Ringer-Bicarbonate solution was 7.11 ± 0.06. Alkalization by HEPES buffer solution (pH 7.4) resulted in pHi 7.54 ± 0.16. Intracellular alkalization induced by HEPES solution significantly hyperpolarized transepithelial voltage, while net potassium flux increased from −17.3 ± 3.6 to −21.0 ± 3.4 pmol·min−1·mm−1. However, lumen-to-bath isotope sodium flux did not change. The basolateral membrane voltage of the principal cells increased from −74.6 ± 3.0 to −79.6 ± 2.9 mV and transepithelial resistance decreased significantly from 113.1 ± 2.7 to 100.9 ± 20.1 Ω·cm2. The calculated fractional resistance of the apical membrane decreased, indicating that intracellular alkalosis increases apical potassium conductance. In the presence of either basolateral ouabain, luminal amiloride, or luminal barium, the HEPES-induced hyperpolarization was preserved. Conclusion. The present study demonstrates that intracellular pH is an important determinant of apical potassium conductance in CCD. Additionally, it should be noted that in the experiments using HEPES buffer solution, intracellular pH in certain epithelial cells was alkalinized by the elimination of bicarbonate and CO2.

Enhanced Volume-Sensitive K Flux in Patients on Chronic Hemodialysis

Swelling-activated K flux was investigated in erythrocytes from patients on regular hemodialysis. K influx, measured by 86Rb uptake, was increased in hemodialysis patients from 25.5 +/- 0.6 to 47.3 +/- 3.4 nmol/10(9) cells/h (n = 4, p < 0.01), when the medium osmolarity of Hepes buffer was decreased by 100 mosm/kg H2O. In normal subjects, K influx was also stimulated from 28.1 +/- 1.2 to 37.8 +/- 2.1 nmol/10(9) cells/h (n = 4, p < 0.01). The swelling-activated increment of K influx was comparatively higher in hemodialysis patients (85.5 vs. 34.5% in controls). Reduction of the medium osmolarity by 100 mosm/kg H2O also caused a larger increase of K efflux in hemodialysis patients than in control subjects (171.1 vs. 118.1%). K efflux was increased even in the presence of 10(-4) M ouabain (from 284 +/- 25 to 879 +/- 122 nmol/10(9) cells/h), although the increment of K efflux was completely abolished when Cl was replaced by gluconate (555 +/- 47 nmol/10(9) cells/h with Cl and 467 +/- 44 nmol/10(9) cells/h without Cl). These data suggest that in hemodialysis patients, swelling-activated K transport is enhanced via activation of the Cl-dependent ouabain-insensitive K transport pathway.

Hydrothorax in a patient on CAPD therapy: Successful treatment with autologous blood pleurodesis.

症例は14歳女性. 慢性腎炎による慢性腎不全のため平成3年2月CAPD導入となった. 6か月後に咳嗽, 軽度呼吸困難が出現したため入院した. 胸部X線で右側胸水が認められた. 胸水中の糖濃度が血糖より高く腹膜透析液の胸腔への移行を疑い99mTcHSAを用いて腹腔胸腔漏の確診を得た. 治療として自家血40ml注入による胸膜癒着術を施行し, 1回注液量を減少させたCAPDを併用した. 3週間後に通常量に戻したが胸水貯留は認められなかった. さらに副作用としての発熱, 胸痛もごく軽度で, 自家血による胸膜癒着術はCAPD横隔膜交通症の治療に有効であると思われた.

Role of Acid-Base Disturbance on Potassium Transport Along the Nephron

We evaluated the role of acidosis on the regulation of transepithelial potassium transport in rabbit early proximal convoluted tubules (PCT) and cortical collecting ducts (CCD) by using in vitro microperfusion and conventional microelectrode methods. In PCT, when the bath medium pH declined from 7.4 to 6.8, transepithelial voltage (Vt) and net potassium flux (JK) increased; however, in CCD, Vt and JK decreased significantly without changing net Na flux. In CCD, basolateral acidosis decreased basolateral membrane voltage and increased transepithelial resistance, with an increment of calculated fractional resistance of apical membrane in principal cells. Inhibition of JK by basolateral acidosis remained significant in the presence of 2mM luminal BaC12. Elimination of ambient bicarbonate (Hepes buffer solution) did not affect the inhibitory effect of basolateral acidosis on JK. Basolateral 1 mM amiloride diminished the inhibitory effect of basolateral acidosis on JK. The 86Rb and 22Na efflux coefficients were not significantly affected by basolateral acidosis.

The correlation of arterial blood pH and erythrocyte potassium concentration in regulaly hemodialized patients

血液透析患者のカリウム (K) 動態を検討する目的で, 前回は透析によるK除去量と赤血球内K濃度を測定した (透析会誌 19 (8), 1986). その結果, 透析前後のK値の変化が同程度でも, Kが細胞外へ流出してK除去が行われる例と, 細胞内へ流入してK除去が少ない例がある事が明らかにされた. 今回は, 透析前後の赤血球内K濃度を測定し, 動脈血pHとの関係を, 血液透析患者12名について検討した. 透析前, 赤血球内K濃度は102.1±3.7mEq/l. cell, 正常者は94.4±0.58mEq/l. cellで, 有意差はなかった. 透析後, 赤血球内K濃度が上昇するもの3例, 低下するもの5例であり, 上昇した3例の透析前動脈血pHは7.229±0.008, 低下した5例は7.336±0.016で有意差を認めた (p<0.01). 赤血球内K濃度の変化と動脈血pHはy=0.084 x-7.30, r=0.74, p<0.01と有意の正相関を示した. 透析前にacidosisが強い例では, 透析後赤血球内K濃度が上昇しKが細胞内に入り込むものと考えられた.

Treatment of fulminant hepatitis by charcoal column with plasma separator

劇症肝炎の治療として, 現在血漿交換 (PEX), 活性炭吸着法 (HP) が用いられるが, PEXでは血清肝炎, HPでは血小板減少などの合併症がある. 今回我々は血漿分離膜を用いて血漿を分離したのち, 回路内にポンプを組み込み, 活性炭吸着筒に通すplasma-perfusion (PP) により劇症肝炎の治療を試み, 若干の知見を得たので報告する. 方法: 旭メディカル社製の血漿分離膜 (AP-05H, AP-08H) を用い血漿を分離した後, 住友ベークライト社製CR-200, CR-300 (活性炭充填量120g) または日本メディカルサプライ社製のBespore® (活性炭充填量80g) 活性炭吸着筒に通した. 対象は軽度から中等度の肝性昏睡を伴った劇症型の肝不全7例. 効果判定は臨床症状および血液検査, 特にビリルビンとアミノ酸分析によって行った. 結果: ビリルビン減少率は, PEXで35.9±3.7%, PPでは22.9±5.2%であった. また同時に実施したアミノ酸分析では, 分枝アミノ酸であるロイシン, イソロイシン, バリンに比して芳香族アミノ酸であるフェニルアラニン, チロジンでより高い減少率が得られた. 芳香族アミノ酸と分枝アミノ酸の比であるFisher scoreを用いた検討では, PP実施中, 時間経過とともにFisher scoreの上昇を認めた. 抗凝固剤としてヘパリンを使用したが使用量は比較的少量で済み, 血小板減少等の副作用は認められなかった. 結論: 1) 血漿分離膜を用いたPPは血小板減少を起こすことなく, またヘパリン使用量も少なく実施可能であった. 2) ビリルビン減少率は22.9%であり血漿交換にはやや劣るもののHP単独よりはるかに有効と考えられた. 3) 肝性脳症の原因の1つと考えられる芳香族アミノ酸の除去に有効であるなどの利点があり, 劇症肝炎の治療に有用であると思われた.