Ando Y, Jacobson H R, Breyer M D
Division of Nephrology, Vanderbilt University, Nashville 37232.
Am J Physiol. 1989 Oct;257(4 Pt 2):F524-30. doi: 10.1152/ajprenal.1989.257.4.F524.
Phosphatidic acid (PA), best known as an intermediate of phosphatidylinositol bisphosphate (PIP2) turnover, inhibits vasopressin (AVP)-induced increase in hydraulic conductivity (Lp) in rabbit cortical collecting ducts (CCD) perfused in vitro (Ando, Y., H. R. Jacobson, and M. D. Breyer, J. Clin. Invest. 80: 590, 1987). The present study addresses the mechanism(s) responsible for this action of PA. In control experiments, 10 microU/ml AVP (23 pM) increased Lp of CCDs from a basal of 4.9 +/- 0.4 X 10(-7) cm.atm-1.s-1 to a peak of 171.2 +/- 4.6 X 10(-7) cm.atm-1.s-1. Basolateral pretreatment of the tubule with PA (25 micrograms/ml) suppressed AVP-induced increase in peak Lp by 45.0%. This suppression was not attenuated by 5 microM indomethacin pretreatment. L-alpha-dipalmitoyl(C16) PA (DPPA, 25 micrograms/ml), an arachidonate-free synthetic PA, inhibited peak Lp by 79.0%, whereas another synthetic PA with shorter fatty acid (C12), L-alpha-dilauroyl PA (DLPA, 25 micrograms/ml), had no significant effect on AVP-induced peak Lp. In the presence of 100 nM staurosporine, a protein kinase C (PKC) inhibitor, the inhibition by PA and DPPA on AVP-induced peak Lp were abolished. Furthermore, another PKC inhibitor, 100 microM 1-(5-isoquiniline-sulfonyl)-2-methylpiperzine, also reversed the DPPA-induced inhibition of AVP action. In separate experiments using fura-2-loaded isolated perfused CCDs, however, neither PA nor DPPA caused a significant increase in intracellular free Ca2+ concentration [( Ca2+]i). Taken together, in CCD, PA-induced inhibition of AVP action is primarily mediated by PKC but not by an increased [Ca2+]i or the production of arachidonate metabolites, such as prostaglandins. Thus the PA-induced activation of PKC does not seem to involve the classic pathway for PKC activation, breakdown of PIP2.
磷脂酸（PA）作为磷脂酰肌醇二磷酸（PIP2）代谢的中间产物最为人所知，它能抑制体外灌注的兔皮质集合管（CCD）中血管加压素（AVP）诱导的水通透率（Lp）增加（安藤洋、H.R.雅各布森和M.D.布雷耶，《临床研究杂志》80:590，1987）。本研究探讨了PA产生这种作用的机制。在对照实验中，10微单位/毫升的AVP（23皮摩尔）使CCD的Lp从基础值4.9±0.4×10⁻⁷厘米·大气压⁻¹·秒⁻¹增加到峰值171.2±4.6×10⁻⁷厘米·大气压⁻¹·秒⁻¹。用PA（25微克/毫升）对肾小管进行基底外侧预处理可使AVP诱导的Lp峰值增加受到45.0%的抑制。5微摩尔吲哚美辛预处理并未减弱这种抑制作用。L-α-二棕榈酰（C16）PA（DPPA，25微克/毫升），一种不含花生四烯酸的合成PA，使Lp峰值受到79.0%的抑制，而另一种脂肪酸较短（C12）的合成PA，L-α-二月桂酰PA（DLPA，25微克/毫升），对AVP诱导的Lp峰值没有显著影响。在存在100纳摩尔星形孢菌素（一种蛋白激酶C（PKC）抑制剂）的情况下，PA和DPPA对AVP诱导的Lp峰值的抑制作用被消除。此外，另一种PKC抑制剂，100微摩尔1-（5-异喹啉磺酰基）-2-甲基哌嗪，也能逆转DPPA对AVP作用的抑制。然而，在使用负载fura-2的分离灌注CCD的单独实验中，PA和DPPA均未引起细胞内游离钙离子浓度[Ca²⁺]i的显著增加。综上所述，在CCD中，PA诱导的对AVP作用的抑制主要由PKC介导，而非通过[Ca²⁺]i增加或花生四烯酸代谢产物如前列腺素的产生。因此，PA诱导的PKC激活似乎不涉及PKC激活的经典途径，即PIP2的分解。
