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Effects of extramitochondrial ADP on permeability transition of mouse liver mitochondria
Zemfira Z Gizatullina1, Ying Chen, Stephan Zierz
1Muskellabor der Neurologischen Klinik der Martin-Luther-Universität Halle-Wittenberg, Ernst-Grube-Str. 40, D-06097 Halle (Saale), Germany. zemfira.gizatullina@rambler.ru
Abstract:
Carboxyatractylate (CAT) and atractylate inhibit the mitochondrial adenine nucleotide translocator (ANT) and stimulate the opening of permeability transition pore (PTP). Following pretreatment of mouse liver mitochondria with 5 microM CAT and 75 microM Ca2+, the activity of PTP increased, but addition of 2 mM ADP inhibited the swelling of mitochondria. Extramitochondrial Ca2+ concentration measured with Calcium-Green 5N evidenced that 2 mM ADP did not remarkably decrease the free Ca2+ but the release of Ca2+ from loaded mitochondria was stopped effectively after addition of 2 mM ADP. CAT caused a remarkable decrease of the maximum amount of calcium ions, which can be accumulated by mitochondria. Addition of 2 mM ADP after 5 microM CAT did not change the respiration, but increased the mitochondrial capacity for Ca2+ at more than five times. Bongkrekic acid (BA) had a biphasic effect on PT. In the first minutes 5 microM BA increased the stability of mitochondrial membrane followed by a pronounced opening of PTP too. BA abolished the action about of 1 mM ADP, but was not able to induce swelling of mitochondria in the presence of 2 mM ADP. We conclude that the outer side of inner mitochondrial membrane has a low affinity sensor for ADP, modifying the activity of PTP. The pathophysiological importance of this process could be an endogenous prevention of PT at conditions of energetic depression.
Insights
Adenine nucleotide translocator inhibitors like Carboxyatractylate (CAT) affect the mitochondrial permeability transition pore (PTP). ADP addition inhibits PTP opening, suggesting a protective role against mitochondrial dysfunction.
Area of Science:
- Mitochondrial physiology
- Cellular respiration
- Biochemistry
Background:
- The mitochondrial adenine nucleotide translocator (ANT) plays a crucial role in energy metabolism.
- Inhibitors like Carboxyatractylate (CAT) and atractylate modulate ANT activity and influence the mitochondrial permeability transition pore (PTP).
- Understanding PTP regulation is vital for comprehending mitochondrial function and dysfunction.
Purpose of the Study:
- To investigate the effects of CAT and ADP on PTP activity and mitochondrial calcium handling.
- To elucidate the role of ADP in modulating PTP opening and mitochondrial stability.
- To explore the potential pathophysiological significance of ADP's interaction with PTP.
Main Methods:
- Mouse liver mitochondria were isolated and pretreated with CAT and Ca2+.
- PTP activity was assessed by measuring mitochondrial swelling.
- Extramitochondrial Ca2+ concentrations were monitored using Calcium-Green 5N.
- Mitochondrial respiration and calcium accumulation capacity were measured.
Main Results:
- CAT and Ca2+ pretreatment increased PTP activity, but ADP inhibited mitochondrial swelling.
- ADP effectively stopped Ca2+ release from loaded mitochondria without significantly reducing free Ca2+.
- CAT decreased mitochondrial calcium-accumulating capacity, while subsequent ADP addition increased it significantly.
- Bongkrekic acid (BA) showed a biphasic effect on PTP, initially stabilizing then promoting opening, and abolished ADP's effect at 1 mM but not 2 mM.
Conclusions:
- A low-affinity ADP sensor on the outer side of the inner mitochondrial membrane modifies PTP activity.
- ADP's interaction with PTP may serve as an endogenous protective mechanism against mitochondrial permeability transition during energetic depression.
- These findings highlight a novel regulatory pathway for PTP and its implications in cellular energy homeostasis.
