T-type Ca2+ signalling regulates aldosterone-induced CREB activation and cell death through PP2A activation in neonatal cardiomyocytes

Aims We have investigated Ca2+ signalling generated by aldosterone-induced T-type current (I-CaT), the effects of I-CaT in neonatal cardiomyocytes, and a putative role for I-CaT in cardiomyocytes during cardiac pathology induced by stenosis in an adult rat. Methods and results Neonatal rat cardiomyocytes treated with aldosterone showed an increase in I-CaT density, principally due to the upregulation of the T-type channel Ca(v)3.1 (by 80%). Aldosterone activated cAMP-response element-binding protein (CREB), and this activation was enhanced by blocking I-CaT or by inhibiting protein phosphatase 2A (PP2A) activity. Aldosterone induced PP2A activity, an induction that was prevented upon I-CaT blockade. I-CaT exerted a negative feedback regulation on the transcription of the Ca(v)3.1 gene, and the activation of PP2A by I-CaT led to increased levels of the pro-apoptotic markers caspase 9 and Bcl-x(S) and decreased levels of the anti-apoptotic marker Bcl-2. These findings were corroborated by flow cytometry analysis for apoptosis and necrosis. Similarly, in a rat model of cardiac disease, I-CaT re-emergence was associated with a decrease in CREB activation and was correlated with increases in caspase 9 and Bcl-x(S) and a decrease in Bcl-2 levels. Conclusion Our findings establish PP2A/CREB as targets of I-CaT-generated Ca2+ signalling and identify an important role for I-CaT in cardiomyocyte cell death.