Takaichi K, Kurokawa K
Fourth Department of Internal Medicine, University of Tokyo School of Medicine, Japan.
J Clin Invest. 1988 Oct;82(4):1437-44. doi: 10.1172/JCI113749.
Vasopressin (AVP) plays a key role in maximal urine concentration by stimulating NaCl reabsorption in the medullary thick ascending limbs of Henle (MAL) and by increasing water permeability in the medullary collecting tubules (MCT). These effects of AVP in MAL and MCT are mediated by cAMP. Alpha 2-adrenergic stimulation in MCT, and high ambient Ca2+ and PGE2 in MAL inhibit AVP-dependent cAMP production and thereby modulate urine concentration. The present study was undertaken to clarify the mechanisms underlying the inhibition of AVP-dependent cAMP production by these agents using microdissected mouse MAL and MCT. Preincubation of MCT and MAL with 1 microgram/ml pertussis toxin for 3 and 6 h, respectively, resulted in ADP-ribosylation of an approximately 41-kD protein, which was presumably an alpha subunit of the inhibitory GTP-binding protein Gi. Epinephrine, 10(-6) M, via alpha 2-adrenergic stimulation, inhibited AVP-dependent cAMP production in MCT. Preincubation of MCT for 3 h with pertussis toxin abolished the inhibition of AVP-dependent cAMP production by epinephrine. High ambient Ca2+ and PGE2 both inhibited AVP-dependent cAMP production in MAL. Preincubation of MAL for 6 h with pertussis toxin abolished the inhibition by high ambient Ca2+ and attenuated the inhibition by PGE2. Preincubation of MCT or MAL with pertussis toxin for 1 h was ineffective in ADP-ribosylation and did not modify the inhibition of AVP-dependent cAMP production by these agents in both nephron segments. Our data suggest that the inhibition of AVP-dependent cAMP production by alpha 2-adrenergic stimulation in MCT, and by high ambient Ca2+ and adrenergic stimulation in MCT, and by high ambient Ca2+ and PGE2 in MAL, is mediated, at least in part, through activation of Gi.
血管加压素（AVP）通过刺激髓袢升支粗段（MAL）对氯化钠的重吸收以及增加髓质集合管（MCT）的水通透性，在最大尿浓缩过程中发挥关键作用。AVP在MAL和MCT中的这些作用是由环磷酸腺苷（cAMP）介导的。MCT中的α2 - 肾上腺素能刺激以及MAL中的高细胞外钙（Ca2+）和前列腺素E2（PGE2）会抑制AVP依赖的cAMP生成，从而调节尿浓缩。本研究旨在使用显微解剖的小鼠MAL和MCT来阐明这些因素抑制AVP依赖的cAMP生成的潜在机制。分别将MCT和MAL与1微克/毫升百日咳毒素预孵育3小时和6小时，导致一种约41-kD的蛋白质发生ADP核糖基化，该蛋白质可能是抑制性GTP结合蛋白Gi的α亚基。10(-6) M的肾上腺素通过α2 - 肾上腺素能刺激抑制了MCT中AVP依赖的cAMP生成。将MCT与百日咳毒素预孵育3小时可消除肾上腺素对AVP依赖的cAMP生成的抑制作用。高细胞外钙和PGE2均抑制了MAL中AVP依赖的cAMP生成。将MAL与百日咳毒素预孵育6小时可消除高细胞外钙的抑制作用，并减弱PGE2的抑制作用。将MCT或MAL与百日咳毒素预孵育1小时对ADP核糖基化无效，并且不会改变这些因素对两个肾单位节段中AVP依赖的cAMP生成的抑制作用。我们的数据表明，MCT中的α2 - 肾上腺素能刺激以及MAL中的高细胞外钙和PGE2对AVP依赖的cAMP生成的抑制作用至少部分是通过Gi的激活介导的。
