Rebouças N A, Malnic G
Departamento de Fisiologia e Biofisica, Universidade de São Paulo, Brazil.
Kidney Blood Press Res. 1996;19(2):87-93. doi: 10.1159/000174049.
The effect of protein kinase C (PKC) activation on fluid and bicarbonate transport in renal tubules has been discussed controversially. Stimulation and inhibition have been shown to depend on factors such as experimental model and exposure time to the mediator of enzyme activation. We studied the role of PKC activation by phorbol-12-myristate-13-acetate (PMA) and by 1,2-dioctanoyl glycerol (DOG) in proximal bicarbonate reabsorption (JHCO3-) by 'in vivo' stationary microperfusion and ion-exchange resin microelectrode determination of luminal pH. Both PMA (10(-8) mol/l) and DOG (10(-3) mol/l) added to lumen or to peritubular capillaries reduced the net JHCO3- significantly. When added to lumen, the inhibition was 44 and 32%, respectively. This reduction did not involve changes in lumen stationary pH, but was mediated by a marked increase in the halftime of luminal bicarbonate disappearance; from 4.22 +/- 0.23 to 6.27 +/- 0.51 s with PMA and from 3.90 +/- 0.25 to 6.33 +/- 0.48 s with DOG. This effect was intensified by 10(-6) mol/l okadaic acid, a phosphatase inhibitor (inhibition of JHCO3- increased to 61%), and reduced by 30% by 10(-6) mol/l H7, an inhibitor of PKC. H89, a protein kinase A inhibitor, did not affect the inhibitory action of PMA. Our data suggest that PKC activation reduces the rate of H ion secretion (bicarbonate reabsorption) in convoluted segments of rat renal proximal tubules and that phosphorylation of the Na+/H+ exchanger by this kinase is the cause of the reduction in net secretion of H ions.
蛋白激酶C（PKC）激活对肾小管液体和碳酸氢盐转运的影响一直存在争议。已表明刺激和抑制作用取决于实验模型和酶激活介质的暴露时间等因素。我们通过“体内”固定微灌注和离子交换树脂微电极测定管腔pH值，研究了佛波醇-12-肉豆蔻酸酯-13-乙酸酯（PMA）和1,2-二辛酰甘油（DOG）激活PKC在近端碳酸氢盐重吸收（JHCO3-）中的作用。向管腔或肾小管周围毛细血管中添加PMA（10^(-8) mol/l）和DOG（10^(-3) mol/l）均显著降低了净JHCO3-。添加到管腔时，抑制率分别为44%和32%。这种降低并不涉及管腔固定pH值的变化，而是由管腔碳酸氢盐消失半衰期的显著延长介导的；PMA作用下从4.22±0.23秒延长至6.27±0.51秒，DOG作用下从3.90±0.25秒延长至6.33±0.48秒。10^(-6) mol/l的磷酸酶抑制剂冈田酸增强了这种作用（JHCO3-的抑制率增加到61%），而10^(-6) mol/l的PKC抑制剂H7使其降低了30%。蛋白激酶A抑制剂H89不影响PMA的抑制作用。我们的数据表明，PKC激活降低了大鼠肾近端小管曲段的H离子分泌速率（碳酸氢盐重吸收），并且该激酶对Na+/H+交换体的磷酸化是H离子净分泌减少的原因。
