Objective: 

We studied if adrenergic stimulation induced production of mitochondrial reactive oxygen species (ROS) in wild type (WT) and obese ob/ob mouse cardiac cells. Also, we studied if ROS affected cardiac Ca²⁺ transients in adrenergic stimulation.

Methods: 

Freshly isolated ob/ob and WT cardiac cells were paced at 1Hz, cytoplasmic Ca²⁺ transients ([Ca²⁺]_i) and mitochondrial superoxide were measured in a confocal microscope using fluorescent dyes Fluo-3 and MitoSOX Red, respectively. As a marker of oxidative stress, malondialdehyde (MDA) modification of proteins was detected with western blotting. 100nM isoproterenol (ISO) was used as beta-adrenergic agonist.

Results: 

ISO increased ROS production in WT cardiac cells. Moreover, WT hearts perfused with ISO for 30 min showed a doubling in MDA relative control. In WT hearts, the amplifying effect of ISO on [Ca²⁺]_i amplitude was diminished in presence of the antioxidant NAC (control: 4.40.32, ISO: 6.60.37, ISO+NAC: 5.20.33); a reduced effect on cell shortening was also seen (increased from 9.81.1 % to 17.91.2 % with ISO and 13.50.9 % with ISO+NAC). In contrast, ob/ob cells did not significantly increase ROS production when exposed to ISO. Control experiments indicated a lower rate of mitochondrial ROS production in ob/ob than WT hearts. The effect of ISO on [Ca²⁺]_i amplitude in ob/ob hearts was not significantly affected by NAC (control: 3.50.22, ISO: 6.00.39, ISO+NAC: 5.60.18).

Conclusion: 

ROS production in heart contributes to the inotropic effect of beta-adrenergic agonists by increasing the amplitude of [Ca²⁺]_i transients. In contrast to general belief, our data suggest that obesity is associated with decreased ROS production in cardiac muscle.