title: Calpeptin, not calpain, directly inhibits an ion channel of the inner mitochondrial membrane.
abstract: The permeability transition pore (PTP) of inner mitochondrial membranes is a large conductance pathway for ions up to 1500 Da which opening is responsible for ion equilibration and loss of membrane potential in apoptosis and thus in several neurodegenerative diseases. The PTP can be regulated by the Ca(2+)-activated mitochondrial K channel (BK). Calpains are Ca(2+)-activated cystein proteases; calpeptin is an inhibitor of calpains. We wondered whether calpain or calpeptin can modulate activity of PTP or BK. Patch clamp experiments were performed on mitoplasts of rat liver (PTP) and of an astrocytoma cell line (BK). Channel-independent open probability (P(o)) was determined (PTP) and, taking into account the number of open levels, NP(o) by single channel analysis (BK). We find that PTP in the presence of Ca(2+) (200 μM) is uninfluenced by calpain (13 nM) and shows insignificant decrease by the calpain inhibitor calpeptin (1 μM). The NP(o) of the BK is insensitive to calpain (54 nM), too. However, it is significantly and reversibly inhibited by the calpain inhibitor calpeptin (IC50 = 42 μM). The results agree with calpeptin-induced activation of the PTP via inhibition of the BK. Screening experiments with respirometry show calpeptin effects, fitting to inhibition of the BK by calpeptin, and strong inhibition of state 3 respiration.
authors.affiliation: Department of Neurology, Otto-von-Guericke-Universität, Leipziger Str. 44, D-39120, Magdeburg, Germany.
authors.forename: Maria
authors.initials: M
authors.lastname: Derksen
authors.affiliation: Ophthalmology, SRH Zentralklinikum Suhl, D-98527, Suhl, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Vorwerk
authors.affiliation: Department of Neurology, Otto-von-Guericke-Universität, Leipziger Str. 44, D-39120, Magdeburg, Germany. detlef.siemen@med.ovgu.de.
authors.forename: Detlef
authors.initials: D
authors.lastname: Siemen
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism; D002154:Calpain / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology*; D002460:Cell Line; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004151:Dipeptides / Q000494:pharmacology*; D006801:Humans; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000037:antagonists & inhibitors* / Q000378:metabolism; D008810:Mice, Inbred C57BL; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism; D033681:Mitochondrial Membrane Transport Proteins / Q000378:metabolism; D051336:Mitochondrial Membranes / Q000187:drug effects* / Q000378:metabolism; D000083162:Mitochondrial Permeability Transition Pore; D018408:Patch-Clamp Techniques; D017208:Rats, Wistar
chemical_list: D015853:Cysteine Proteinase Inhibitors; D004151:Dipeptides; D051036:Large-Conductance Calcium-Activated Potassium Channels; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; C071482:calpeptin; D002154:Calpain
keywords: BK channel; Calpain; Calpain inhibitor; Calpeptin; Mitochondria; Patch clamp; Permeability transition pore