Effects of protein kinase C agonists on Na,K-ATPase activity in rat brain microvessels.

Abstract

In order to study the possible role of C kinase (PKC) on sodium pump of cerebral vessels, we used diacylglycerol (diC8: sn-1,2-dioctanoylglycerol) and phorbol esters (PMA: phorbol 12-myr-istate 13-acetate; PDA: phorbol 12,13-diacetate; 4 oc-P: 4-alpha phorbol) as PKC activators, and examined their effects on Na, KATPase activity in rat brain microvessels (MVs). Rats were divided into non-treated (control; n = 9), four-vessel occlusion (4VO; 30-30 minutes ischemia and recirculation, n = 5), and middle cerebral artery occlusion (MCAO, n = 3) groups. MVs were passed through nylon meshes and were obtained by ultracentrifuge at 58000 g. Na,K-ATPase activity in MVs was determined by the phosphomolybdate method. DiC8 enhanced Na,K-ATPase activity at 10-4M in the control group, the 4VO group and the contralateral hemispheres of the MCAO group (139% ± 0.06**, 135% ± 0.2*, 133% ± 0.18, mean ± SE, * p < 0.05, ** p < 0.01, Wilcoxon rank sum) respectively, but had no effects on MVs in the ipsilateral hemispheres of MCAO group (-74% ± 0.04). This activation by diC8 was inhibited by PKC inhibitors, staurosporine (3 x 10-8M) and H7 (l0-6M) in the control MVs. By contrast, PMA suppressed Na, KATPase at 10-5M in the control group (-25% ±0.07*), but it tended to activate Na,K-ATPase activity in the ipsilateral hemispheres of the MCAO groups (33% ± 0.09). PDA and 4 α-P did not have any consistent effects at the concentration examined. The cause of difference between the effects of diC8 and PMA is unclear at present, but it may stem from the mode of lipid-membrane interaction in these agents and the difference in the condition of cells as well.