T-type Ca 2+ channel blockers prevent cardiac cell hypertrophy through an inhibition of calcineurin–NFAT3 activation as well as L-type Ca 2+ channel blockers

Abstract

T-type Ca 2+ channels (TCCs) are involved in cardiac cell growth and proliferation in cultured cardiomyocytes. Underlying molecular mechanisms are not well understood. In this study, we investigated the role of TCCs in signal transduction in cardiac hypertrophy compared with L-type Ca 2+ channels (LCCs). Cardiomyocytes dissociated from neonatal mouse ventricles were cultured until stabilization. Cell hypertrophy was induced by reapplication of 1% fatal bovine serum (FBS) following a period (24 h) of FBS depletion. Cell surface area increased from 862 ± 73 μm 2 to 2153 ± 131 μm 2 by FBS stimulation in control (250 ± 1.8%). T-type Ca 2+ current ( I CaT) was inhibited dose-dependently by kurtoxin (KT) and efonidipine (ED) with IC 50 0.07 μM and 3.2 μM, respectively in whole-cell voltage clamp. On the other hand, 1 μM KT which inhibits I CaT over 90% did not effect on L-type Ca 2+ current ( I CaL). 10 μM ED had the ability of I CaL blockade as well as that of I CaT blockade. 3 μM nisoldipine (ND) suppressed I CaL by over 80%. The increase in cell surface area following reapplication of FBS as observed in control (250 ± 1.8%) was significantly reduced in the presence of 1 µM KT (216 ± 1.2%) and virtually abolished in the presence of 10 µM ED (97 ± 0.8%) and 3 μM ND (80 ± 1.1%). Hypertrophy was associated with an increase in BNP mRNA of 316 ± 3.6% in control and this increase was reduced as well in the presence of 1 µM KT (254 ± 1.8%) and almost abolished in the presence of 10 µM ED (116 ± 1.1%) and 3 μM ND (93 ± 0.8%). Immunolabeling showed that translocation of nuclear factor of activated T cells (NFAT3) into the nucleus in response to FBS stimulation was markedly inhibited by either KT or ED as well as ND. Calcineurin phosphatase activity was upregulated 2.2-fold by FBS, but KT, ED and ND decreased this upregulation (1.7-fold, 0.8-fold, and 0.7-fold with KT, ED and ND respectively). These results suggest that blockade of Ca 2+ entry into cardiomyocytes via TCCs may block pathophysiological signaling pathways leading to hypertrophy as well as via LCCs. The mechanism may be the inhibition of calcineurin-mediated NFAT3 activation resulting in prevention of its translocation into the nucleus.