Dataset Information

The mitochondrial Na+-Ca2+ exchanger, NCLX, regulates automaticity of HL-1 cardiomyocytes.

ABSTRACT: Mitochondrial Ca(2+) is known to change dynamically, regulating mitochondrial as well as cellular functions such as energy metabolism and apoptosis. The NCLX gene encodes the mitochondrial Na(+)-Ca(2+) exchanger (NCXmit), a Ca(2+) extrusion system in mitochondria. Here we report that the NCLX regulates automaticity of the HL-1 cardiomyocytes. NCLX knockdown using siRNA resulted in the marked prolongation of the cycle length of spontaneous Ca(2+) oscillation and action potential generation. The upstrokes of action potential and Ca(2+) transient were markedly slower, and sarcoplasmic reticulum (SR) Ca(2+) handling were compromised in the NCLX knockdown cells. Analyses using a mathematical model of HL-1 cardiomyocytes demonstrated that blocking NCXmit reduced the SR Ca(2+) content to slow spontaneous SR Ca(2+) leak, which is a trigger of automaticity. We propose that NCLX is a novel molecule to regulate automaticity of cardiomyocytes via modulating SR Ca(2+) handling.

SUBMITTER: Takeuchi A

PROVIDER: S-EPMC3783885 | biostudies-other | 2013

REPOSITORIES: biostudies-other

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The mitochondrial Na+-Ca2+ exchanger, NCLX, regulates automaticity of HL-1 cardiomyocytes.

Takeuchi Ayako A Kim Bongju B Matsuoka Satoshi S

Scientific reports 20130926

Mitochondrial Ca(2+) is known to change dynamically, regulating mitochondrial as well as cellular functions such as energy metabolism and apoptosis. The NCLX gene encodes the mitochondrial Na(+)-Ca(2+) exchanger (NCXmit), a Ca(2+) extrusion system in mitochondria. Here we report that the NCLX regulates automaticity of the HL-1 cardiomyocytes. NCLX knockdown using siRNA resulted in the marked prolongation of the cycle length of spontaneous Ca(2+) oscillation and action potential generation. The u ...[more]

PMID: 24067497

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Project description:In adult cardiomyocytes (CMs), the Na(+)/Ca(2+) exchanger (NCX) is a well-defined determinant of Ca(2+) homeostasis. Developmentally, global NCX knockout in mice leads to abnormal myofibrillar organization, electrical defects, and early embryonic death. Little is known about the expression and function of NCX in human heart development. Self-renewable, pluripotent human embryonic stem cells (hESCs) can serve as an excellent experimental model. However, hESC-derived CMs are highly heterogeneous. A stably lentivirus-transduced hESC line (MLC2v-dsRed) was generated to express dsRed under the transcriptional control of the ventricular-restricted myosin light chain-2v (MLC2v) promoter. Electrophysiologically, dsRed+ cells differentiated from MLC2vdsRed hESCs displayed ventricular action potentials (AP), exclusively. Neither atrial nor pacemaker APs were observed. While I(Ca-L), I(f), and I(Kr) were robustly expressed, I(Ks) and I(K1) were absent in dsRed+ ventricular hESCCMs. Upon differentiation (7+40 to +90 days), the basal [Ca(2+)](i), Ca(2+) transient amplitude, maximum upstroke, and decay velocities significantly increased (P < 0.05). The I(Ca-L) antagonizer nifedipine (1 microM) decreased the Ca(2+) transient amplitude (to approximately 30%) and slowed the kinetics (by approximately 2-fold), but Ca(2+) transients could still be elicited even after complete ICa-L blockade, suggesting the presence of additional Ca(2+) influx(es). Indeed, Ni(2+)-sensitive INCX could be recorded in 7+40- and +90-day dsRed+ hESC-CMs, and its densities increased from -1.2 +/- 0.6 pA/pF at -120 mV and 3.6 +/- 1.0 pA/pF at 60 mV by 6- and 2-folds, respectively. With higher [Ca(2+)](i), 7+90-day ventricular hESC-CMs spontaneously but irregularly fired transients upon a single stimulus under an external Na(+)-free condition; however, without extracellular Na(+), nifedipine could completely inhibit Ca(2+) transients. We conclude that I(NCX) is functionally expressed in developing ventricular hESC-CMs and contributes to their excitation-contraction coupling.

Dataset Information

The mitochondrial Na+-Ca2+ exchanger, NCLX, regulates automaticity of HL-1 cardiomyocytes.

Publications

The mitochondrial Na+-Ca2+ exchanger, NCLX, regulates automaticity of HL-1 cardiomyocytes.

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