ENDOTHELIUM STIMULATES THE VASCULAR SMOOTH-MUSCLE CELL NA K PUMP OF NORMOTENSIVE AND HYPERTENSIVE RATS BY A PROTEIN-KINASE-C PATHWAY/

Objective To investigate the mechanisms involved in the endothelial st imulation of the vascular smooth muscle cell Na/K pump and their possi ble alteration by hypertension. Methods The Na/K pump activity of vasc ular smooth muscle cells (VSMC) from normotensive Wistar-Kyoto (WKY) r ats and spontaneously hypertensive rats (SHR) was studied using the ra dioactive analogue of K+ Rb-86(+). Conditioned medium of bovine endoth elial aortic cells was used to investigate the endothelial modulation of VSMC Na/K pump activity. Results Conditioned medium enhanced VSMC N a/K pump activity (ouabain-sensitive Rb-86(+) uptake), this effect bei ng higher in SHR cells. This stimulatory effect was neither modified i n Na+-loaded cells from both rat strains nor inhibited by the Na/H exc hange blocker amiloride. Permeable analogues of cyclic adenosine and g uanosine monophosphates did not modify the baseline VSMC Na/K pump act ivity of WKY rats and SHR, and subsequently the guanylate cyclase inhi bitor methylene blue did not alter the conditioned medium-induced stim ulation of the pump. However, the Ca2+-channel inhibitor nifedipine re duced the Na/K pump stimulation by conditioned medium, this decrease b eing higher in WKY rat than in SHR VSMC. Moreover, treatment with phor bol 12,13-dibutyrate for 24 h or with the protein kinase C inhibitor s taurosporine for 15 min reduced the conditioned medium-induced Na/K pu mp activation in both VSMC cultures. Conclusions Na/K pump stimulation by conditioned medium of endothelial cells is mediated mainly via act ivation of protein kinase C in VSMC from either WKY or SHR VSMC. Howev er, SHR VSMC show some alterations in their intracellular signalling p athways.