Calcium Elevation in Mitochondria Is the Main Ca2+ Requirement for Mitochondrial Permeability Transition Pore (mPTP) Opening

Abstract

We have investigated in detail the role of intra-organelle Ca2+ content during induction of apoptosis by the oxidant menadione while changing and monitoring the Ca2+ load of endoplasmic reticulum (ER), mitochondria, and acidic organelles. Menadione causes production of reactive oxygen species, induction of oxidative stress, and subsequently apoptosis. In both pancreatic acinar and pancreatic tumor AR42J cells, menadione was found to induce repetitive cytosolic Ca2+ responses because of the release of Ca2+ from both ER and acidic stores. Ca2+ responses to menadione were accompanied by elevation of Ca2+ in mitochondria, mitochondrial depolarization, and mitochondrial permeability transition pore (mPTP) opening. Emptying of both the ER and acidic Ca2+ stores did not necessarily prevent menadione-induced apoptosis. High mitochondrial Ca2+ at the time of menadione application was the major factor determining cell fate. However, if mitochondria were prevented from loading with Ca2+ with 10 μm RU360, then caspase-9 activation did not occur irrespective of the content of other Ca2+ stores. These results were confirmed by ratiometric measurements of intramitochondrial Ca2+ with pericam. We conclude that elevated Ca2+ in mitochondria is the crucial factor in determining whether cells undergo oxidative stress-induced apoptosis.

VDAC1 selectively transfers apoptotic Ca2+ signals to mitochondria

“…We applied an oxidative stress, that is, treated the cells acutely with 1 mM H 2 O 2 . As previously reported, 23 the addition of H 2 O 2 caused a [Ca 2 þ ] cyt increase that is much smaller and more sustained than that evoked by histamine (Figures 6a and b). Under those conditions, mitochondria also undergo a small increase (peak value o1 mM).…”

“…À7.5 ± 2.5%; siRNA-hVDAC1 27.4 ± 1.5%; siRNA-hVDAC2 À45.9 ± 3.5%; c, Control À6.5 ± 2.1%; siRNA-hVDAC1 þ 30.9 ± 3.9%; siRNA-hVDAC2 À45.2 ± 2.3%; d, Control À4 ± 5.3%; siRNA-hVDAC1 þ 24.3 ± 5.1%; siRNA-hVDAC2 À50.1 ± 6.8%) 23 This latter event has been proposed to represent a sort of priming signal that conditions and sensitizes mitochondria to otherwise non-lethal stimuli. In this context, the local coupling between ER and mitochondrial Ca 2 þ channels becomes critically relevant: small Ca 2 þ microdomains elicited by apoptotic stimuli such as C2-ceramide strongly relies on the existence of a preferential route transmitting the signal from the ER to the mitochondrion; on the other side, during physiological signals large Ca 2 þ microdomains are generated and this fine channel coupling could be potentially overwhelmed by the vigorous ER Ca 2 þ release.…”

“…21 Indeed, mitochondrial Ca 2 þ accumulation acts as a 'priming signal' sensitizing the organelle and promoting the release of caspase cofactors, both in isolated mitochondria as well as in intact cells. 22,23 In this context, ER-mitochondria contacts mediate the tight and efficient Ca 2 þ transmission between the two organelles and thus could represent a potential regulatory site for cell death signals. 24 Here we investigate the role of the different VDAC isoforms in the context of cell sensitivity to apoptosis and their role in regulating ER-mitochondrial Ca 2 þ signals transmission, and demonstrated that VDAC1, by selectively interacting with the IP 3 Rs, is preferentially involved in the transmission of the low-amplitude apoptotic Ca 2 þ signals to mitochondria.…”

Terpinen-4-ol Induces Autophagic and Apoptotic Cell Death in Human Leukemic HL-60 Cells

“…The oxidative stressor induces two independent apoptotic pathways within pancreatic acinar cells, viz., the classical mitochondrial calcium-dependent pathway that is initiated rapidly in the majority of cells, and a slower, caspase-8-mediated pathway that depends on the lysosomal activities of cathepsins and is used when the caspase-9 pathway is disabled (Baumgartner et al, 2007). The present study demonstrated that HL-60 cells induced high caspase-8 activity and led to the cleavage of Bid protein without the MTP reduction.…”

Untitled

“…Вплив О-карбоксиметилгідроксиламіну (О-СМН; 50 мг/кг) на показники кардіодинаміки ізольованого серця щурів за умов збільшення концентрації кальцію у перфузій-ному розчині: а -тиск у лівому шлуночку; б -коронарний потік; в -швидкість скорочення міокарда; г -інтенсивність скоротливої функції; 1 -контроль, 2 -дія О-СМН Пригнічення мітохондріального шляху синтезу сірководню погіршує скоротливу функцію серця серця та мітохондріях знижується, а відтак серце стає більш чутливим до ішемічно-ре-перфузійного пошкодження [13]. Окрім того, що Са 2+ регулює перебіг циклу Кребса та є активатором низки інших ферментів, у високій концентрації -це при-родний індуктор відкривання МП перемінної проникності [14]. У попередніх досліджен-нях було виявлено, що донор сірководню NaHS, внесений екзогенно у концентрації 10 -5 моль/л, попереджає відкривання МП, що проявлялося у зниженні набухання органел на тлі дії кальцію порівняно з таким у кон-трольних тварин [15].…”