Mitochondria-derived reactive oxygen species and vascular MAP kinases - Comparison of angiotensin II and diazoxide

Reactive oxygen species ( ROS) are key mediators in signal transduction of angiotensin II ( Ang II). However, roles of vascular mitochondria, a major intracellular ROS source, in response to Ang II stimuli have not been elucidated. This study aimed to examine the involvement of mitochondria- derived ROS in the signaling pathway and the vasoconstrictor mechanism of Ang II. Using 5- hydroxydecanoate ( 5- HD; a specific inhibitor of mitochondrial ATP- sensitive potassium [ mitoK(ATP)] channels) and tempol ( a superoxide dismutase mimetic), the effects of Ang II and diazoxide ( a mitoK(ATP) channel opener) were compared on redox- sensitive mitogen- activated protein ( MAP) kinase activation in rat vascular smooth muscle cells ( RVSMCs) in vitro and in rat aorta in vivo. Stimulation of RVSMCs by Ang II or diazoxide increased phosphorylated MAP kinases ( ERK1/ 2, p38, and JNK), as well as superoxide production, which were then suppressed by 5- HD pretreatment in a dose- dependent manner, except for ERK1/ 2 activation by Ang II. The same events were reproduced in rat aorta in vivo. Ang II- like diazoxide depolarized the mitochondrial membrane potential ( DeltaPsi(M)) of RVSMCs determined by JC- 1 fluorescence, which was inhibited by 5- HD. 5- HD did not modulate Ang II - induced calcium mobilization in RVSMCs and did not affect on the vasoconstrictor effect in either acute or chronic phases of Ang II - induced hypertension. These results reveal that Ang II stimulates mitochondrial ROS production through the opening of mitoK(ATP) channels in the vasculature- like diazoxide, leading to reduction of DeltaPsi(M) and redox- sensitive activation of MAP kinase; however, generated ROS from mitochondria do not contribute to Ang II - induced vasoconstriction.