Abstract 11503: IP3 Mediated Calcium Release Regulates Mitochondrial Metabolism In Cardiac Myocytes
Background: In cardiac myocytes huge calcium (Ca) amounts are getting released with each beat. Therefore it is astonishing that myocytes also use Ca signals for local signaling purposes. In mitochondria distinct Ca signals are messengers for metabolic adaptation and apoptosis induction. In nonexcitable cells Ca signaling via inositol 1,4,5-trisphosphate (IP3) is a key factor of local Ca signals. The mechanisms cardiac myocytes are using to distinguish between general Ca release for contraction and local Ca signaling still need to be elucidated. Hypothesis: In microdomains of mitochondria and the sarcoplasmatic reticulum (SR), mitochondria take up Ca released from the SR by IP3. This Ca uptake is uncoupled from the general cytoplasmatic Ca release during contraction and does influence metabolic activity.
Methods: Isolated adult mice ventricular myocytes were examined using confocal microsopy. Intact cells were loaded with X-Rhod and incubated in manganese chloride to quench cytoplasmatic fluorescence. For permeabilization cells were treated with digitonin for 30-60 sec. Mitochondrial membrane potential ([[Unable to Display Character: ∆]][[Unable to Display Character: Ѱ]]m) and ROS were measured by loading cells with TMRM and mitoSOX respectively.
Results: The stimulation of the myocytes with the IP3 agonists endothelin-1 (ET-1, 10 nM) and angiotensin-2 (AngII, 2 µM) resulted in a strong increase of mitochondrial Ca. The ET-1 mediated increase was stronger (21±5% after 20 min, n=18, p<0.01) than the one mediated by AngII (14±5% after 20 min, n=10, p<0.05). In both cases the observed increase could be blocked completely by 3 µM of the IP3R antagonist 2-APB. These results were confirmed in permeabilized cells using 1 µM of the IP3 receptor agonist adenophostin. The observed effect on mitochondrial Ca was much bigger and faster (40±7% in 1 min, 62±11% in 10 min, n=4, p<0.01). 2-APB blocked mitochondrial Ca uptake mediated by adenophostin only incompletely. The observed mitochondrial Ca uptake was accompanied by an increase in ROS production (+26±2% in 20 min, n=8) and the depolarization of [[Unable to Display Character: ∆]][[Unable to Display Character: Ѱ]]m (-36±4% in 20 min, n=10)). Both could be blocked completely by 2-APB.
Conclusion: IP3 mediated mitochondrial Ca uptake plays a significant role in the cellular adaptation of mitochondrial metabolism and ROS production.
- © 2012 by American Heart Association, Inc.