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.