Faculty Collaboration Database

Slow Ca²⁺ Efflux by Ca²⁺/H⁺ Exchange in Cardiac Mitochondria Is Modulated by Ca²⁺ Re-uptake via MCU, Extra-Mitochondrial pH, and H⁺ Pumping by F_OF₁-ATPase. Front Physiol 2018;9:1914

Date

02/26/2019

Pubmed ID

30804812

Pubmed Central ID

PMC6378946

DOI

10.3389/fphys.2018.01914

Scopus ID

2-s2.0-85065923980 (requires institutional sign-in at Scopus site)   10 Citations

Abstract

Mitochondrial (m) Ca²⁺ influx is largely dependent on membrane potential (ΔΨ_m), whereas mCa²⁺ efflux occurs primarily via Ca²⁺ ion exchangers. We probed the kinetics of Ca²⁺/H⁺ exchange (CHE_m) in guinea pig cardiac muscle mitochondria. We tested if net mCa²⁺ flux is altered during a matrix inward H⁺ leak that is dependent on matrix H⁺ pumping by ATP_m hydrolysis at complex V (F_OF₁-ATPase). We measured [Ca²⁺]_m, extra-mitochondrial (e) [Ca²⁺]_e, ΔΨ_m, pH_m, pH_e, NADH, respiration, ADP/ATP ratios, and total [ATP]_m in the presence or absence of protonophore dinitrophenol (DNP), mitochondrial uniporter (MCU) blocker Ru360, and complex V blocker oligomycin (OMN). We proposed that net slow influx/efflux of Ca²⁺ after adding DNP and CaCl₂ is dependent on whether the ΔpH_m gradient is/is not maintained by reciprocal outward H⁺ pumping by complex V. We found that adding CaCl₂ enhanced DNP-induced increases in respiration and decreases in ΔΨ_m while [ATP]_m decreased, ΔpH_m gradient was maintained, and [Ca²⁺]_m continued to increase slowly, indicating net mCa²⁺ influx via MCU. In contrast, with complex V blocked by OMN, adding DNP and CaCl₂ caused larger declines in ΔΨ_m as well as a slow fall in pH_m to near pH_e while [Ca²⁺]_m continued to decrease slowly, indicating net mCa²⁺ efflux in exchange for H⁺ influx (CHE_m) until the ΔpH_m gradient was abolished. The kinetics of slow mCa²⁺ efflux with slow H⁺ influx via CHE_m was also observed at pH_e 6.9 vs. 7.6 by the slow fall in pH_m until ΔpH_m was abolished; if Ca²⁺ reuptake via the MCU was also blocked, mCa²⁺ efflux via CHE_m became more evident. Of the two components of the proton electrochemical gradient, our results indicate that CHE_m activity is driven largely by the ΔpH_m chemical gradient with H⁺ leak, while mCa²⁺ entry via MCU depends largely on the charge gradient ΔΨ_m. A fall in ΔΨ_m with excess mCa²⁺ loading can occur during cardiac cell stress. Cardiac cell injury due to mCa²⁺ overload may be reduced by temporarily inhibiting F_OF₁-ATPase from pumping H⁺ due to ΔΨ_m depolarization. This action would prevent additional slow mCa²⁺ loading via MCU and permit activation of CHE_m to mediate efflux of mCa²⁺. HIGHLIGHTS -We examined how slow mitochondrial (m) Ca²⁺ efflux via Ca²⁺/H⁺ exchange (CHE_m) is triggered by matrix acidity after a rapid increase in [Ca²⁺]_m by adding CaCl₂ in the presence of dinitrophenol (DNP) to permit H⁺ influx, and oligomycin (OMN) to block H⁺ pumping via F_OF₁-ATP synthase/ase (complex V).-Declines in ΔΨ_m and pH_m after DNP and added CaCl₂ were larger when complex V was blocked.-[Ca²⁺]_m slowly increased despite a fall in ΔΨ_m but maintained pH_m when H⁺ pumping by complex V was permitted.-[Ca²⁺]_m slowly decreased and external [Ca²⁺]_e increased with declines in both ΔΨ_m and pH_m when complex V was blocked.-ATP_m hydrolysis supports a falling pH_m and redox state and promotes a slow increase in [Ca²⁺]_m.-After rapid Ca²⁺ i

Author List

Haumann J, Camara AKS, Gadicherla AK, Navarro CD, Boelens AD, Blomeyer CA, Dash RK, Boswell MR, Kwok WM, Stowe DF

Authors

Amadou K. Camara PhD Professor in the Anesthesiology department at Medical College of Wisconsin
Ranjan K. Dash PhD Professor in the Biomedical Engineering department at Medical College of Wisconsin
Wai-Meng Kwok PhD Professor in the Anesthesiology department at Medical College of Wisconsin
David F. Stowe MD, PhD Professor in the Anesthesiology department at Medical College of Wisconsin