Abstract 107: Mitochondrial Depolarization without Reactive Oxygen Species Production leads to Augmented Cerebral Vascular Relaxation via Diverse Calcium-related events in Smooth Muscle and Endothelium
Introduction: Mitochondrial depolarization and subsequent generation of reactive oxygen species (ROS) in vascular smooth muscle cells (VSMC) trigger vasodilation by diazoxide, a putative mitochondrial KATP channel (mitoKATP) opener, via activation of ‘Ca2+-sparks’ (CS) and Ca2+-activated K+ channels. It is unclear if mitochondrial depolarization, independent of ROS, promotes CS. In addition, the contribution to dilation of calcium events in endothelium following mitochondrial activation is unclear. Previously, we reported reduced vasodilation of cerebral arteries of insulin resistant (IR) Zucker obese (ZO) compared to lean (ZL) rats. Therefore, we examined the effect of BMS-191095 (BMS), a mitoKATP opener that does not affect ROS generation, on cerebral arteries of Sprague-Dawley (SD) and ZL rats. In addition, we evaluated the impact of mitochondrial dysfunction due to IR in ZO rats.
Methods: Fluorescence microscopy was used to measure the CS and global calcium (Fluo-4 AM), mitochondrial membrane potential (TMRE), ROS (mitoSOX), and nitric oxide (DAF) in segments of pressurized, cerebral arteries. Diameters were determined continuously with an automated system.
Results: In SD arteries, BMS (50 umol/L) depolarized mitochondria without producing ROS. BMS also enhanced generation of CS (54±9 versus 117±18 sparks/min in response to vehicle and BMS respectively, p<0.05). Baseline CS activity (sparks/min) was reduced in ZO compared to ZL (156±21 versus 231±26, p<0.05). BMS and DZ responses were diminished in ZO (207±48 and 257±32, p=NS) versus ZL (318±54 and 366±63). In addition, BMS increased global calcium and nitric oxide production by endothelium.
Conclusions: Mitochondrial depolarization induces Ca2+-sparks in VSM and increased global calcium in endothelium via ROS-independent mechanisms. Thus, mitochondria can be depolarized without an associated increase in ROS levels. In addition, mitochondrial dysfunction associated with IR impaired CS activity leading to reduced mitochondrial mediated vasodilation. Thus, even a relatively mild metabolic disease such as IR, is able to disrupt coupling between mitochondrial status and vascular tone.
- © 2012 by American Heart Association, Inc.