Gesek F A
Department of Pharmacology and Toxicology, Dartmouth Medical School, Hanover, New Hampshire 03755.
Am J Physiol. 1993 Oct;265(4 Pt 2):F561-8. doi: 10.1152/ajprenal.1993.265.4.F561.
The influence of alpha-adrenoceptor subtypes on Na+ transport in distal convoluted tubules (DCT) has not been examined due to the difficulty of isolating and quantifying responses in this segment. These experiments were designed to test the hypothesis that alpha-adrenergic receptors stimulate Na+ absorption in DCT cells. Norepinephrine and epinephrine increased 22Na+ uptake into immortalized mouse DCT cells by 49 and 55% compared with basal uptake. Selective alpha 2-agonists (guanabenz, clonidine, and B-HT 933) stimulated 22Na+ uptake by 39-45%, but alpha 1-agonists had no effect. alpha 2-Agonist-stimulated 22Na+ uptake was abolished with alpha 2-antagonists (yohimbine, idazoxan). The entry pathways for alpha 2-agonist-stimulated 22Na+ uptake were determined with the NaCl cotransport inhibitor, chlorothiazide (10(-4) M), and the Na+ channel blocker, amiloride (10(-6) M). Agonist-stimulated 22Na+ uptake was inhibited 42 +/- 5 with chlorothiazide and 47 +/- 7% with amiloride. These results suggested that alpha 2-receptors may activate Na(+)-K(+)-adenosinetriphosphatase (Na(+)-K(+)-ATPase), resulting in an increased driving force for luminal Na+ entry through both pathways. Ouabain-suppressible 86Rb uptake and intracellular Na+ activity ([Na+]i; measured in single cells on glass cover slips loaded with the fluorescent probe sodium-binding benzofuran isophthalate) were used to measure Na(+)-K(+)-ATPase activity. alpha 2-Agonists significantly increased 86Rb uptake within 30 s. After 2.5 min, epinephrine and B-HT 933 decreased [Na+]i from a control level of 13 +/- 1 to 5 +/- 1 mM.(ABSTRACT TRUNCATED AT 250 WORDS)
由于在分离和定量该节段反应方面存在困难，α-肾上腺素能受体亚型对远曲小管（DCT）中Na+转运的影响尚未得到研究。这些实验旨在检验α-肾上腺素能受体刺激DCT细胞中Na+吸收的假说。与基础摄取相比，去甲肾上腺素和肾上腺素使永生化小鼠DCT细胞对22Na+的摄取增加了49%和55%。选择性α2-激动剂（胍那苄、可乐定和B-HT 933）使22Na+摄取增加了39%-45%，但α1-激动剂无作用。α2-拮抗剂（育亨宾、咪唑克生）可消除α2-激动剂刺激的22Na+摄取。用NaCl共转运抑制剂氯噻嗪（10(-4) M）和Na+通道阻滞剂阿米洛利（10(-6) M）确定α2-激动剂刺激22Na+摄取的进入途径。氯噻嗪使激动剂刺激的22Na+摄取抑制42±5，阿米洛利使其抑制47±7%。这些结果表明，α2-受体可能激活Na(+)-K(+)-三磷酸腺苷酶（Na(+)-K(+)-ATP酶），导致通过两条途径使管腔Na+进入的驱动力增加。哇巴因可抑制的86Rb摄取和细胞内Na+活性（[Na+]i；在装载有荧光探针钠结合苯并呋喃异酞酸酯的玻璃盖玻片上的单细胞中测量）用于测量Na(+)-K(+)-ATP酶活性。α2-激动剂在30秒内显著增加86Rb摄取。2.5分钟后，肾上腺素和B-HT 933使[Na+]i从对照水平的13±1降至5±1 mM。（摘要截短于250字）
