Martin K J, McConkey C L, Jacob A K, Gonzalez E A, Khan M, Baldassare J J
Department of Internal Medicine, St. Louis University School of Medicine, Missouri 63110.
Am J Physiol. 1994 Feb;266(2 Pt 2):F254-8. doi: 10.1152/ajprenal.1994.266.2.F254.
The relative roles of the adenylate cyclase-protein kinase A system (AC-PKA), the phospholipase C-protein kinase C system (PLC-PKC), and increases in cytosolic calcium in mediating the final actions of parathyroid hormone (PTH) remain ill defined. Although an important role for the PLC-PKC system in the regulation of phosphate transport in response to PTH has been suggested, previous studies from our laboratory and others, in OK cells, have emphasized the major role of AC-PKA. The present studies were designed to dissociate the second messengers for PTH by using an inhibitor of PLC (U-73,122). Studies were performed in confluent cultures of OK cells with and without preincubation with U-73,122 (1 microM). This inhibitor did not alter adenosine 3',5'-cyclic monophosphate (cAMP) production or the activation of PKA in response to PTH. Preincubation with U-73,122, however, totally abolished PTH-stimulated increases in diglyceride mass, consistent with inhibition of PLC. Activation of particulate PKC was then examined in response to PTH in the absence and presence of U-73,122. Although PTH resulted in an increase in particulate PKC activity in control cultures, this effect was abolished in the presence of U-73,122 and actually decreased significantly. Therefore, having documented marked attenuation of PLC-PKC, we next examined the effects of PTH on phosphate transport. Basal phosphate uptake was not altered by 1 microM U-73,122. Dose-response curves of the inhibition of phosphate transport in response to PTH were identical in the presence or absence of U-73,122. Thus inhibition of PLC and PKC activities did not alter the effects of PTH on phosphate transport.(ABSTRACT TRUNCATED AT 250 WORDS)
腺苷酸环化酶 - 蛋白激酶A系统（AC - PKA）、磷脂酶C - 蛋白激酶C系统（PLC - PKC）以及胞质钙增加在介导甲状旁腺激素（PTH）最终作用中的相对作用仍不明确。尽管已有研究表明PLC - PKC系统在PTH调节磷酸盐转运中起重要作用，但我们实验室及其他实验室之前在OK细胞中的研究强调了AC - PKA的主要作用。本研究旨在通过使用PLC抑制剂（U - 73,122）来区分PTH的第二信使。研究在OK细胞汇合培养物中进行，细胞在有无1μM U - 73,122预孵育的情况下进行实验。该抑制剂不会改变腺苷3',5'-环磷酸（cAMP）的产生或PKA对PTH的激活反应。然而，用U - 73,122预孵育完全消除了PTH刺激的二酰甘油量增加，这与PLC的抑制一致。然后在有无U - 73,122的情况下检测PTH对颗粒型PKC激活的影响。尽管PTH使对照培养物中的颗粒型PKC活性增加，但在U - 73,122存在时这种作用被消除，实际上还显著降低。因此，在证明PLC - PKC明显减弱后，我们接下来检测PTH对磷酸盐转运的影响。1μM U - 73,122不会改变基础磷酸盐摄取。在有无U - 73,122的情况下，PTH抑制磷酸盐转运的剂量反应曲线相同。因此，抑制PLC和PKC活性不会改变PTH对磷酸盐转运的影响。（摘要截断于250字）
