Abstract 15545: Ca2+ Influx Through L-type Ca2+ Channels Activates Nuclear Factor of Activated T-cells Translocation in Neonatal Rat Ventricular Myocytes
Introduction: In cardiomyocytes, pathological stress increases cytosolic Ca2+, which activates Calcineurin (Cn) that dephosphorylates nuclear factor of activated T-cells (NFAT), thus inducing nuclear translocation where it initiates pathological hypertrophy. The sources of Ca2+ that initiate hypertrophy through Cn-NFAT signaling pathway are still not clearly established. Recent studies suggest that Cn-NFAT activation may be independent of the global cardiac Ca2+ transient and may take place in signaling microdomains housing either L- or T-type Ca2+ channels or Transient Receptor Potential (TRP) channels.
Hypothesis: We tested the hypothesis that Ca2+ influx through L-type Ca2+ channels (LTCCs) is sufficient to induce NFAT nuclear translocation.
Methods and Results: Experiments were performed with neonatal rat ventricular myocytes (NRVMs) infected with adenovirus encoding NFATc3-GFP. NRVMs express L- and T-type Ca2+ channels and TRP channels. Exposure of NRVMs to 4 mM Ca2+ induced NFAT nuclear translocation (GFP fluorescence intensity ratio, nucleus/cytoplasm (firn/c), was 20.25 ± 1.33 in 4 mM Ca2+-treated cells, n=45, vs. 1.00 ± 0.07 in control, n=22, P<0.0001). Nifedipine (a dihydropyridine LTCC antagonist, 10 µM) blocked NFAT translocation (firn/c was 1.48 ± 0.16, n=19). Ni2+ (a T-type Ca2+ channel antagonist, 50 µM) had no effect on NFAT translocation. SKF-96365 (a TRP channel blocker, 5 µM) also blocked NFAT translocation (firn/c was 4.71 ± 1.10, n=27). Overexpression of TRPC3 induced NFAT translocation and hypertrophy. A dominant negative TRPC6 partially blocked NFAT translocation induced by 4 mM Ca2+ (by 70%), but did not inhibit hypertrophy induced by 100 µM phenylephrine. Nifedipine (10 µM) completely blocked NFAT translocation induced by TRPC3 overexpression. Diltiazem (a non-dihydropyridine LTCC blocker, 100 µM) completely inhibited NRVM hypertrophy induced by phenylephrine, which was not inhibited by SKF-96365.
Conclusions: Ca2+ influx through LTCCs is sufficient to induce NFAT nuclear translocation and hypertrophy. TRP channels appear to have a minor role and T-type Ca2+ channels do not appear to activate pathological hypertrophy signaling.
- © 2011 by American Heart Association, Inc.