During excitation contraction coupling, calcium (Ca2+) released by ryanodine receptors (RyR2) enters in the mitochondria through the mitochondrial calcium uniporter (MCU). The MCU is a macromolecular complex composed by MCU and its regulatory proteins, MICU1 and MICU2. Under metabolic syndrome, mitochondrial Ca2+ uptake is decreased and we recently observed an increase in MICU1 expression after two weeks of High fat High Sucrose diet (HFS).

To determine whether increase MICU1 expression impact the MCU function and may account for the decrease in mitochondrial Ca2+ uptake, our aim was to characterize the single channel electrophysiological properties of the MCU incorporated in planar lipid bilayer.

MCU was purified from mice heart from control or 2 weeks HFS diet group. Mitochondria were isolated by differential centrifugation, and treated with proteinase K and digitonin to disrupt the outer mitochondrial membrane. Purified MCU was then incorporated in planar lipid bilayer to study its biophysical properties. Voltage steps were applied from -60mV to +60mV. At −40mV, Ca2+ concentration was increased from 1μM to 1mM. Ruthenium red (RuR; 100μM) was used to inhibit the single channel activity.

At low Ca2+ concentration, the MCU purified from the HFS heart have a reduced number of opening events. The opening probability (Po) and the opening frequency (Fo) are significantly reduced compared to the control heart. However, at high Ca2+ concentration (100μM) the MCU Po, the Fo and the number of events with high amplitude are increased whereas in control the single channels behavior remained unchanged.

After 2 weeks of HFS diet, the increase of MICU1 expression affects biophysical properties of the MCU. Indeed, at low calcium concentrations MICU1 acts as a channel inhibitor and reduced MCU activity, but under high calcium concentrations MICU1 may acts as a channel activator for the MCU complex.