Abstract 630 Local Calcium Control Of Mitochondrial Membrane Potential And Permeability Transition Pore By Calmodulin In Rat Ventricular Myocytes.
[Background] An increase in [Ca2+]i after beta1 adrenergic receptor stimulation is known to activate calmodulin (CaM) and Ca2+/CaM-dependent protein kinase II (CaMKII), resulting in a promotion of apoptosis in cardiac myocytes.
[Purpose and Methods] To clarify the potential role of CaM and CaMKII on the process of apoptosis, we evaluated the effects of CaM on mitochondrial membrane potential (DeltaPsi(m)) and permeability transition pore (mPTP) in saponin-permeabilized rat ventricular myocytes with a laser scanning confocal microscopy.
CaM ([Ca2+]i = 177 nM) depolarized DeltaPsi(m) dose-dependently (66.0±4.8%, 53.4±3.7%, 45.2±5.7% and 46.6±5.5% of the baseline for 1 nM, 10 nM, 100 nM and 1 μM, respectively, p<0.05). CaM-induced depolarization of DeltaPsi(m) was partially prevented by W-7 (an inhibitor of CaM: 100 nM) and by an inhibitor of CaMKII (CaMKII 290–309: 10 nM).
Application of 10 nM, 100 nM and 1 μM CaM significantly accelerated the leakage of calcein from mitochondria. Calcein intensities decreased to 80.1±1.3%, 79.1±2.2% and 79.6±1.7% of the baseline, respectively (p<0.05). These effects of CaM were prevented by W-7 (100 nM) and CaMKII 290–309 (10 nM) (92.1±1.2%, and 98.0±1.7%, respectively; p<0.05 vs 10 nM CaM).
Cyclosporin A (an inhibitor of mPTP: 0.2 μM) prevented both CaM-induced depolarization of DeltaPsi(m) (92.5±4.7%, p<0.05 vs 177 nM [Ca2+]i) and acceleration of calcein leakage (92.3±2.6%, p<0.05).
Thapsigargin (an inhibitor of SERCA: 10 μM ), and BAPTA (5 mM) eliminated the effects of CaM on DeltaPsi(m) (88.7±3.1%, 85.4±2.4%, respectively, p<0.05 vs 177 nM [Ca2+]i).
[Conclusion] Both CaM itself and CaMKII altered mitochondrial function by depolarizing DeltaPsi(m) and by opening mPTP. These effects of CaM and CaMKII on mitochondria were strictly regulated by the local increase in [Ca2+], established by the Ca2+ releases from the sarcoplasmic reticulum.