Abstract
In cardiomyocytes, intracellular calcium (Ca2+) transients are elicited by electrical and receptor stimulations, leading to muscle contraction and gene expression, respectively. Although such elevations of Ca2+levels ([Ca2+]) also occur in the nucleus, the precise mechanism of nuclear [Ca2+] regulation during different kinds of stimuli, and its relationship with cytoplasmic [Ca2+] regulation are not fully understood. To address these issues, we used a new region-specific fluorescent protein-based Ca2+ indicator, GECO, together with the conventional probe Fluo-4 AM. We confirmed that nuclear Ca2+ transients were elicited by both electrical and receptor stimulations in neonatal mouse ventricular myocytes. Kinetic analysis revealed that electrical stimulation-elicited nuclear Ca2+ transients are slower than cytoplasmic Ca2+ transients, and chelating cytoplasmic Ca2+ abolished nuclear Ca2+ transients, suggesting that nuclear Ca2+ are mainly derived from the cytoplasm during electrical stimulation. On the other hand, receptor stimulation such as with insulin-like growth factor-1 (IGF-1) preferentially increased nuclear [Ca2+] compared to cytoplasmic [Ca2+]. Experiments using inhibitors revealed that electrical and receptor stimulation-elicited Ca2+ transients were mainly mediated by ryanodine receptors and inositol 1,4,5-trisphosphate receptors (IP3Rs), respectively, suggesting different mechanisms for the two signals. Furthermore, IGF-1-elicited nuclear Ca2+ transient amplitude was significantly lower in myocytes lacking neuronal Ca2+ sensor-1 (NCS-1), a Ca2+ binding protein implicated in IP3R-mediated pathway in the heart. Moreover, IGF-1 strengthened the interaction between NCS-1 and IP3R. These results suggest a novel mechanism for receptor stimulation-induced nuclear [Ca2+] regulation mediated by IP3R and NCS-1 that may further fine-tune cardiac Ca2+ signal regulation.
Highlights
Intracellular calcium (Ca2+) regulates various cellular functions
A more detailed analysis using the line-scan technique (Fig 1D) indicated that the kinetics of the nuclear Ca2+ transients were significantly slower than those of the cytoplasmic transients (Fig 1E), i.e. both time to peak and T1/2 of decline were significantly delayed (Fig 1F and 1G). These results suggest that electrical stimulation-elicited nuclear Ca2+ transients follow the dynamics of cytoplasmic [Ca2+]
To investigate which intracellular Ca2+ release channels are involved in the electrical stimulation-elicited nuclear Ca2+ transients, we examined the effects of various inhibitors
Summary
Intracellular calcium (Ca2+) regulates various cellular functions. In the heart, it is essential for muscle contraction, which is regulated by excitation-contraction (E-C) coupling [1]. Regulation of Nuclear Ca2+ Signaling in the Heart: A Role of NCS-1. Cerebral and Cardiovascular Center #22-2-3 that SW received. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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