title: Blockade of calcium influx through L-type calcium channels attenuates mitochondrial injury and apoptosis in hypoxic renal tubular cells.
abstract: In hypoxia, ATP depletion causes cellular Ca(2+) increase, mitochondrial injury, and apoptosis in renal tubular cells. However, the molecular basis of these observations is incompletely delineated. IRPTC, a rat renal proximal tubular cell line, was treated with antimycin A, and disturbances in cytoplasmic calcium ([Ca(2+)]c) and mitochondrial calcium ion concentration ([Ca(2+)]m), dissipation of mitochondrial membrane potential (DeltaPsi(m)), cytochrome c release, and resultant apoptosis were examined. Pharmacologic targeting of L-type Ca(2+) channels in vitro and in vivo was used to clarify the involvement of voltage-dependent Ca(2+) channels during this process. In vitro studies indicated that ATP depletion-induced apoptosis was preceded by increased [Ca(2+)]c and [Ca(2+)]m before activation of mitochondrial signaling. Antagonizing L-type Ca(2+) channels offset these findings, suggesting [Ca(2+)]c and [Ca(2+)]m involvement. Azelnidipine administration ameliorated cellular and mitochondrial Ca(2+) accumulation, mitochondrial permeability transition, cytochrome c release, caspase-9 activation, and resultant apoptosis (15.8 +/- 0.8% versus 8.9 +/- 0.7%; P < 0.01). Similar effects of azelnidipine were substantiated in an in vivo ischemia/reperfusion injury model. There were fewer terminal-deoxynucleotidyl transferase mediated dUTP nick-end labeling-positive cells in the azelnidipine-treated group (0.322 +/- 0.038/tubule) as compared with the vehicle-treated group (0.450 +/- 0.041; P < 0.05), although the antiapoptotic effect was smaller in vivo than in vitro, partly as a result of distinct levels of Bax expression. It is proposed that voltage-dependent Ca(2+) channels are involved in cellular and mitochondrial accumulation of Ca(2+) subsequent to ATP depletion and play an important role in regulating mitochondrial permeability transition, cytochrome c release, caspase activation, and apoptosis.
authors.affiliation: Division of Nephrology and Endocrinology, University of Tokyo School of Medicine, 7-3-1, Hongo, Bunkyo-ku, Tokyo, Japan. mnangaku-tky@umin.ac.jp
authors.forename: Tetsuhiro
authors.initials: T
authors.lastname: Tanaka
authors.forename: Masaomi
authors.initials: M
authors.lastname: Nangaku
authors.forename: Toshio
authors.initials: T
authors.lastname: Miyata
authors.forename: Reiko
authors.initials: R
authors.lastname: Inagi
authors.forename: Takamoto
authors.initials: T
authors.lastname: Ohse
authors.forename: Julie R
authors.initials: JR
authors.lastname: Ingelfinger
authors.forename: Toshiro
authors.initials: T
authors.lastname: Fujita
mesh_terms: D000818:Animals; D000968:Antimycin A / Q000494:pharmacology; D017209:Apoptosis; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000502:physiology*; D015687:Cell Hypoxia; D002478:Cells, Cultured; D007684:Kidney Tubules / Q000166:cytology / Q000378:metabolism* / Q000473:pathology*; D008297:Male; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D020746:Calcium Channels, L-Type; D000968:Antimycin A; D002118:Calcium