title: Ca2+ paradox injury mediated through TRPC channels in mouse ventricular myocytes.
abstract: BACKGROUND AND PURPOSE The Ca(2+) paradox is an important phenomenon associated with Ca(2+) overload-mediated cellular injury in myocardium. The present study was undertaken to elucidate molecular and cellular mechanisms for the development of the Ca(2+) paradox. EXPERIMENTAL APPROACH Fluorescence imaging was performed on fluo-3 loaded quiescent mouse ventricular myocytes using confocal laser scanning microscope. KEY RESULTS The Ca(2+) paradox was readily evoked by restoration of the extracellular Ca(2+) following 10-20 min of nominally Ca(2+)-free superfusion. The Ca(2+) paradox was significantly reduced by blockers of transient receptor potential canonical (TRPC) channels (2-aminoethoxydiphenyl borate, Gd(3+), La(3+)) and anti-TRPC1 antibody. The sarcoplasmic reticulum (SR) Ca(2+) content, assessed by caffeine application, gradually declined during Ca(2+)-free superfusion, which was further accelerated by metabolic inhibition. Block of SR Ca(2+) leak by tetracaine prevented Ca(2+) paradox. The Na(+) /Ca(2+) exchange (NCX) blocker KB-R7943 significantly inhibited Ca(2+) paradox when applied throughout superfusion period, but had little effect when added for a period of 3 min before and during Ca(2+) restoration. The SR Ca(2+) content was better preserved during Ca(2+) depletion by KB-R7943. Immunocytochemistry confirmed the expression of TRPC1, in addition to TRPC3 and TRPC4, in mouse ventricular myocytes. CONCLUSIONS AND IMPLICATIONS These results provide evidence that (i) the Ca(2+) paradox is primarily mediated by Ca(2+) entry through TRPC (probably TRPC1) channels that are presumably activated by SR Ca(2+) depletion; and (ii) reverse mode NCX contributes little to the Ca(2+) paradox, whereas inhibition of NCX during Ca(2+) depletion improves SR Ca(2+) loading, and is associated with reduced incidence of Ca(2+) paradox in mouse ventricular myocytes.
authors: Department of Anesthesiology, Shiga University of Medical Science, Otsu, Shiga, Japan.
authors: Akiko
authors: A
authors: Kojima
authors: Hirotoshi
authors: H
authors: Kitagawa
authors: Mariko
authors: M
authors: Omatsu-Kanbe
authors: Hiroshi
authors: H
authors: Matsuura
authors: Shuichi
authors: S
authors: Nosaka
mesh_terms: D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000009:adverse effects* / Q000378:metabolism; D004195:Disease Models, Animal; D006335:Heart Injuries / Q000378:metabolism*; D006352:Heart Ventricles / Q000293:injuries / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors; D050052:TRPC Cation Channels / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000187:drug effects / Q000502:physiology*; D013748:Tetracaine / Q000494:pharmacology; D013890:Thiourea / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: C101670:2-(2-(4-(4-nitrobenzyloxy)phenyl)ethyl)isothiourea methanesulfonate; D019831:Sodium-Calcium Exchanger; D050052:TRPC Cation Channels; D013748:Tetracaine; D002110:Caffeine; D013890:Thiourea; D002118:Calcium