Voltage-dependent anion channel 2 modulates resting Ca²+ sparks, but not action potential-induced Ca²+ signaling in cardiac myocytes.
Voltage-dependent anion channels (VDACs) are pore forming proteins predominantly found in the outer mitochondrial membrane and are thought to transport Ca(2+). In this study, we have investigated the possible role of type 2 VDAC (VDAC2) in cardiac Ca(2+) signaling and Ca(2+) sparks using a lentiviral knock-down (KD) technique and two-dimensional confocal Ca(2+) imaging in immortalized autorhythmic adult atrial cells, HL-1. We confirmed high expression of VDAC2 protein in ventricular, atrial, and HL-1 cells using Western blot analysis. Infection of HL-1 cells with VDAC2-targeting lentivirus reduced the level of VDAC2 protein to ∼10%. Comparisons of autorhythmic Ca(2+) transients between wild-type (WT) and VDAC2 KD cells showed no significant change in the magnitude, decay, and beating rate of the Ca(2+) transients. Caffeine (10mM)-induced Ca(2+) release, which indicates sarcoplasmic reticulum (SR) Ca(2+) content, was not altered by VDAC2 KD. Interestingly, however, the intensity, width, and duration of the individual Ca(2+) sparks were significantly increased by VDAC2 KD in resting conditions, with no change in the frequency of sparks. VDAC2 KD significantly delayed mitochondrial Ca(2+) uptake during artificial Ca(2+) pulses in permeabilized HL-1 cells. These results suggest that VDAC2 may facilitate mitochondrial Ca(2+) uptake and restrict Ca(2+) spark expansion without regulating activations of sparks under resting conditions, thereby providing evidence on the functional role of VDAC2 in cardiac local Ca(2+) signaling.
College of Pharmacy, IDRD, Chungnam National University, 220 Gung-dong, Yuseong-gu, Daejeon 305-764, South Korea.
Krishna Prasad
KP
Subedi
Joon-Chul
JC
Kim
Moonkyung
M
Kang
Min-Jeong
MJ
Son
Yeon-Soo
YS
Kim
Sun-Hee
SH
Woo
D000200:Action Potentials; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D002461:Cell Line, Transformed; D051379:Mice; D032383:Myocytes, Cardiac / Q000166:cytology / Q000378:metabolism*; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D050996:Voltage-Dependent Anion Channel 2 / Q000235:genetics / Q000378:metabolism*
D034741:RNA, Small Interfering; D050996:Voltage-Dependent Anion Channel 2; D002110:Caffeine; D002118:Calcium