Specific vulnerability of mouse spinal cord motoneurons to membrane depolarization.
Intracellular calcium (Ca(2+)) concentration determines neuronal dependence on neurotrophic factors (NTFs) and susceptibility to cell death. Ca(2+) overload induces neuronal death and the consequences are thought to be a probable cause of motoneuron (MN) degeneration in neurodegenerative diseases. In the present study, we show that membrane depolarization with elevated extracellular potassium (K(+)) was toxic to cultured embryonic mouse spinal cord MNs even in the presence of NTFs. Membrane depolarization induced an intracellular Ca(2+) increase. Depolarization-induced toxicity and increased intracellular Ca(2+) were blocked by treatment with antagonists to some of the voltage-gated Ca(2+) channels (VGCCs), indicating that Ca(2+) influx through these channels contributed to the toxic effect of depolarization. Ca(2+) activates the calpains, cysteine proteases that degrade a variety of substrates, causing cell death. We investigated the functional involvement of calpain using a calpain inhibitor and calpain gene silencing. Pre-treatment of MNs with calpeptin (a cell-permeable calpain inhibitor) rescued MNs survival; calpain RNA interference had the same protective effect, indicating that endogenous calpain contributes to the cell death caused by membrane depolarization. These findings suggest that MNs are especially vulnerable to extracellular K(+) concentration, which induces cell death by causing both intracellular Ca(2+) increase and calpain activation.
Gou-Fabregas
Myriam
M
Neuronal Signaling Unit, Department Ciències Médiques Bàsiques, Facultat de Medicina, Universitat de Lleida-IRBLLEIDA, Montserrat Roig, Lleida, Spain.
Garcera
Ana
A
Mincheva
Stefka
S
Perez-Garcia
M Jose
MJ
Comella
Joan X
JX
Soler
Rosa M
RM
D000704:Analysis of Variance; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D016923:Cell Death / Q000187:drug effects; D002478:Cells, Cultured; D002642:Chick Embryo; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004622:Embryo, Mammalian; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D049452:Green Fluorescent Proteins / Q000235:genetics; D018398:Homeodomain Proteins / Q000378:metabolism; D007424:Intracellular Fluid / Q000187:drug effects / Q000378:metabolism; D060850:LIM-Homeodomain Proteins; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology*; D009414:Nerve Growth Factors / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000494:pharmacology; D013116:Spinal Cord / Q000166:cytology*; D013997:Time Factors; D014157:Transcription Factors
D002121:Calcium Channel Blockers; D004791:Enzyme Inhibitors; D018691:Excitatory Amino Acid Antagonists; D018398:Homeodomain Proteins; D060850:LIM-Homeodomain Proteins; D009414:Nerve Growth Factors; D034741:RNA, Small Interfering; D014157:Transcription Factors; C063843:insulin gene enhancer binding protein Isl-1; D049452:Green Fluorescent Proteins; D011189:Potassium Chloride; D002118:Calcium