Menè P, Pugliese F, Cinotti G A
Chair of Nephrology, University of Rome La Sapienza, Italy.
Exp Nephrol. 1993 Jul-Aug;1(4):245-52.
Na+/Ca2+ exchange contributes to the control of cytosolic free Ca2+ levels ([Ca2+]i) in resting and activated cultured human mesangial cells. We have previously shown that activation of phospholipase C by vasoconstrictors enhances Ca2+ influx upon extracellular Na+ withdrawal. This effect is not mediated by concurrent activation of protein kinase (PK) C, since it occurs even after PKC inhibition, and phorbol esters actually blunt both basal and stimulated Na+/Ca2+ exchange. We now studied the effects of PKA and PKG activation by adenylate/guanylate cyclase stimuli or by permeant analogues of cyclic nucleotides in monolayer cultures loaded with the fluorescent Ca(2+)-sensitive probe, fura-2. The exchanger was inhibited by the stable prostaglandin I2 analogue, iloprost, which is transduced by cAMP (peak [Ca2+]i inhibition by 1 microM iloprost 35 +/- 3%). Similarly, non-receptor activation of adenylate cyclase by 10 microM forskolin inhibited basal and agonist-stimulated Na+/Ca2+ exchange by 52 +/- 4 and 66 +/- 4%, respectively. Dibutyryl-cAMP (0.1 mM) also inhibited stimulated Na(+)-dependent Ca2+ influx by 72 +/- 2%. The particulate guanylate cyclase agonist, atriopeptin III, and the soluble guanylate cyclase activator, glyceryltrinitrate, also inhibited both basal and angiotensin II-stimulated Na+Ca2+ exchange (to a maximum of 53 +/- 5 and 62 +/- 3%, respectively). Dibutyryl-cGMP (1 mM) mimicked the effects of cGMP stimuli, reducing stimulated Na+/Ca2+ exchange by 79 +/- 2%. Therefore, similar to PKC, cyclic nucleotide activation of PKA and PKG regulates Na+/Ca2+ exchange, providing a functional link between transmembrane signalling systems for vasoactive agents in cultured human mesangial cells.
钠钙交换有助于调控静息及激活状态下培养的人系膜细胞内的胞质游离钙水平（[Ca2+]i）。我们之前已经表明，血管收缩剂激活磷脂酶C可增强细胞外钠去除时的钙内流。这种效应并非由蛋白激酶（PK）C的同时激活介导，因为即便在PKC受到抑制后该效应仍会出现，而且佛波酯实际上会减弱基础及刺激状态下的钠钙交换。我们现在通过腺苷酸/鸟苷酸环化酶刺激物或环核苷酸的渗透性类似物激活蛋白激酶A（PKA）和蛋白激酶G（PKG），并在加载了荧光钙敏感探针fura-2的单层培养物中研究其效应。稳定的前列腺素I2类似物伊洛前列素可抑制该交换体，伊洛前列素通过环磷酸腺苷（cAMP）传导（1 μM伊洛前列素使[Ca2+]i峰值抑制35±3%）。同样，10 μM福斯可林对腺苷酸环化酶的非受体激活分别使基础及激动剂刺激的钠钙交换抑制52±4%和66±4%。二丁酰环磷腺苷（0.1 mM）也使刺激状态下的钠依赖性钙内流抑制72±2%。颗粒性鸟苷酸环化酶激动剂心房钠尿肽III及可溶性鸟苷酸环化酶激活剂硝酸甘油也抑制基础及血管紧张素II刺激的钠钙交换（分别最大抑制至53±5%和62±3%）。二丁酰环磷鸟苷（1 mM）模拟了环磷酸鸟苷（cGMP）刺激的效应，使刺激状态下的钠钙交换减少79±2%。因此，与PKC类似，PKA和PKG的环核苷酸激活可调节钠钙交换，为培养的人系膜细胞中血管活性物质的跨膜信号系统提供了功能联系。
