Liedtke C M
Department of Pediatrics, Rainbow Babies and Children Hospital, Cleveland, Ohio.
Am J Physiol. 1990 Aug;259(2 Pt 1):L66-72. doi: 10.1152/ajplung.1990.259.2.L66.
The marked sensitivity of Cl and fluid secretion in mammalian airways to basolateral application of loop diuretics has led to postulates that electrically neutral Na-Cl entry plays a critical role during secretion. Electrically neutral Na-Cl(K) cotransport was investigated by determining the initial rate of 22Na and 36Cl efflux in epithelial cells isolated from rabbit trachea and preequilibrated with radioactive tracer at 25 degrees C. Tracer transport was initiated by 10-fold dilution of an aliquot of cells in radioisotope-free medium. The initial rate of radiolabeled ion transport was calculated from the linear portion of efflux curves. Base-line Na and Cl transport rates were not affected by furosemide or bumetanide. l-Epinephrine stimulated Na and Cl transport rates 1.8-fold each in Ca2(+)-replete and 2.6- and 2.3-fold, respectively, in Ca2(+)-deficient transport medium. Loop diuretics and yohimbine, an alpha 2-adrenergic antagonist, blocked the effects of l-epinephrine, and, clonidine, an alpha 2-adrenergic agonist, stimulated yohimbine- and furosemide-sensitive Cl transport. The beta-adrenergic agonist l-isoproterenol alone did not affect tracer transport and, in combination with clonidine, did not affect the response to clonidine. Elevation of intracellular Ca2+ with ionomycin stimulated tracer transport, and buffering of intracellular Ca2+ with 1,2-bis(aminophenoxy)ethane- N,N,N',N'-tetraacetic acid blocked the stimulatory effects of alpha-adrenergic agents. These results indicate an alpha 2-adrenergic stimulation of loop diuretic-sensitive Na and Cl transport that requires elevated intracellular Ca2+ as the second messenger. The transport mechanism is probably a Na-Cl or Na-K-2Cl cotransport located in the basolateral membrane.
哺乳动物气道中氯离子（Cl）和液体分泌对基底外侧应用袢利尿剂具有显著敏感性，这使得人们推测电中性的钠-氯进入在分泌过程中起关键作用。通过测定从兔气管分离的上皮细胞中22Na和36Cl流出的初始速率，研究了电中性钠-氯（钾）共转运，这些细胞在25℃下用放射性示踪剂进行预平衡。示踪剂转运通过在无放射性同位素的培养基中对一份细胞进行10倍稀释来启动。放射性标记离子转运的初始速率根据流出曲线的线性部分计算得出。基线钠和氯的转运速率不受呋塞米或布美他尼的影响。在富含Ca2+的转运培养基中，l-肾上腺素分别刺激钠和氯的转运速率1.8倍，在缺乏Ca2+的转运培养基中分别刺激2.6倍和2.3倍。袢利尿剂和α2-肾上腺素能拮抗剂育亨宾阻断了l-肾上腺素的作用，而α2-肾上腺素能激动剂可乐定刺激了对育亨宾和呋塞米敏感的氯转运。β-肾上腺素能激动剂l-异丙肾上腺素单独不影响示踪剂转运，与可乐定联合使用时也不影响对可乐定的反应。用离子霉素升高细胞内Ca2+刺激示踪剂转运，用1,2-双（氨基苯氧基）乙烷-N,N,N',N'-四乙酸缓冲细胞内Ca2+可阻断α-肾上腺素能药物的刺激作用。这些结果表明，α2-肾上腺素能刺激袢利尿剂敏感的钠和氯转运，这需要升高的细胞内Ca2+作为第二信使。转运机制可能是位于基底外侧膜的钠-氯或钠-钾-2氯共转运。
