Mitochondrial membrane potential modulates regulation of mitochondrial Ca²⁺in rat ventricular myocytes

Abstract

]m reduction. Cytosolic Na ϩ concentrations that yielded one-half maximal activity levels for mitoNCX were 3.6 mM at normal ⌬⌿ m and 7.6 mM at ⌬⌿m dissipation. We conclude that 1) the mitochondrial Ca 2ϩ uniporter accumulates Ca 2ϩ in a manner that is dependent on ⌬⌿m at the physiological range of [Ca 2ϩ ]c; 2) ⌬⌿m dissipation opens the mPTP and results in Ca 2ϩ influx to mitochondria; and 3) although mitoNCX activity is impaired, mitoNCX extrudes Ca 2ϩ from the matrix even after ⌬⌿m dissipation. permeability transition pore; Na ϩ /Ca 2ϩ exchange; depolarization; ischemia-reperfusion injury ACCUMULATING EVIDENCE REVEALS that mitochondria play primary roles in fatal cell damage during ischemia-reperfusion (33). Key events that occur during ischemia include cytosolic Ca 2ϩ elevation, ATP depletion, high P i concentration, depolarized membrane potential, and acidotic pH. On reperfusion and recovery of normal pH, a burst of reactive oxygen species occurs, mitochondrial Ca 2ϩ overload ensues, and these lead to opening of the mitochondrial permeability transition pore (mPTP; Refs. 8,12,34). Opening of the mPTP allows water and solutes Յ1,500 Da in size to enter the matrix and cause mitochondrial swelling, rupture of the outer mitochondrial membrane, and release of cytochrome c or apoptosis-inducing factor, which initiates apoptotic programmed cell death (12,24,34). Because previous studies (8,12,13) (10,11). Furthermore, recent studies (4,8,10,11,18) also suggest a possible contribution by the mPTP to Ca 2ϩ homeostasis in both the cytosol and mitochondria. Despite the considerable attention given to the pathophysiological significance of mitochondrial Ca 2ϩ , the regulation and/or modulation of mitochondrial Ca 2ϩ during pathophysiological conditions such as ischemia-reperfusion injury are unclear. In previous studies, information about mitochondrial Ca 2ϩ was obtained using isolated mitochondria, whereby the structural and functional properties of organelles were seriously affected, and other cellular architectures were separated from the mitochondria. In this study, we measured [Ca 2ϩ ] m in saponin-permeabilized rat ventricular myocytes and investigated how ⌬⌿ m depolarization affects [Ca 2ϩ ] m and mitochondrial Ca 2ϩ transport systems such as the Ca 2ϩ uniporter, the mPTP, and mitoNCX.

A Computational Model of Cytosolic and Mitochondrial [Ca2+] in Paced Rat Ventricular Myocytes

“…It also depolarizes △Ψm by dissipating H ＋ gradient across the inner membrane of mitochondria, which could affect ionic homeostasis in mitochondria [70]. ]i and decrease SR content and subsequent SR Ca 2＋ release, which is in agreement with our results.…”

“…It also depolarizes △Ψm by dissipating H ＋ gradient across the inner membrane of mitochondria, which could affect ionic homeostasis in mitochondria [70]. Major consequences of uncoupling oxidative phosphorylation result from block or inhibition of ATP synthesis [71][72][73].…”

“…Depolarization of △Ψm itself can affect the ion movement across the inner membrane of mitochondria. Saotome et al [70] found that FCCP decreased [Ca 2＋ ]m in a dose-dependent manner. They also suggested that dissipation of △Ψm opens the mitochondrial permeability transition pore (mPTP).…”

Microtubule Disorganization Affects the Mitochondrial Permeability Transition Pore in Cardiac Myocytes

“…We used pa- age fluorescent indicator, tetramethylrhodamine ethyl ester (TMRE, 10 nmol/L), and the mPTP opening was measured with a calcein acetoxymethyl ester (calcein AM, 1 μmol/L) as described previously. 17 All measurements were performed with a laser scanning confocal microscope coupled to an inverted microscope (Axiovert 200M, Karl-Zeiss) with a 40× waterimmersion objective lens.…”

Protein Kinase A Catalytic Subunit Alters Cardiac Mitochondrial Redox State and Membrane Potential Via the Formation of Reactive Oxygen Species

“…23 By using permeabilized myocytes, the condition of the extramitochondrial medium (ie, cytosolic Ca 2+ and ATP concentrations) was controlled precisely, without changing the intracellular architecture. 20,24,25 In intact myocytes, the stimulation of BAR increases [Ca 2+ ]i and the dynamic alteration in [Ca 2+ ]i leads to the changes in [Ca 2+ ]m and thus mitochondrial function. These effects of [Ca 2+ ]i were excluded in skinned myocytes.…”