Figure 4. Acute versus chronic regulation of mitochondrial Ca²⁺ and metabolism due to MCU activity.

(A) State 3 mitochondrial oxygen consumption in purified cardiac mitochondria from the indicated mice stimulated with 100 μM Ca²⁺ with or without 2 μM Ru360. *P<0.05 versus ADP baseline; #P<0.05 versus Mcu^fl/fl Ca²⁺. All values presented as mean ± SEM.

(B) Mitochondrial ATP synthesis in isolated mitochondria at baseline and stimulated with 400 μM CaCl₂. 5 μM Ru360 was used as a control. *P<0.05 versus ADP baseline; #P<0.05 versus Mcu^fl/fl Ca²⁺. All values presented as mean ± SEM.

(C) Relative oxygen consumption rates (OCR) of Mcu^fl/fl control adult cardiomyocytes with or without Ru360 (5 μM) in response to 3.125 nM isoproterenol.

(D) OCR in Mcu^fl/fl-MCM vs. Mcu^fl/fl adult cardiomyocytes in response to 3.125 nM isoproterenol. *P<0.05 versus control. All values presented as mean ± SEM.

(E) Maximal rates of cardiac contraction as measured in a closed chest mouse in response to increasing doses of dobutamine. Dobutamine was increased from 0 to 32 ng/g/min and then maintained at 32 ng/g/min for an additional hour. *P<0.05 versus control. All values presented as mean ± SEM.

(F) Total mitochondrial Ca²⁺ content measured from hearts taken at the indicated time-points from indicated groups of mice following dobutamine administration of the experiment shown in E. *P<0.05 versus control. All values presented as mean ± SEM.

(G) Treadmill performance as quantified by maximum sprint time in the Mcu^fl/fl-MCM vs. Mcu^fl/fl controls. Animals were subjected to two different protocols where they were allowed either a 2 minute warm-up or a 30 minute warm-up before reaching maximum sprint speed. *P<0.05 versus control. Number of mice used is shown in the bars. All values presented as mean ± SEM.

See also Figures S2 and S3.