The insulin IGF-1 -PI3K-Akt signaling pathway has been suggested to improve cardiac inotropism and increase Ca2+handling through the effects of the protein kinase Akt. However, the underlying molecular mechanisms remain largely unknown. In this study, we provide evidence for an unanticipated regulatory function of Akt controlling L-type Ca2+channel (LTCC) protein density. The pore-forming channel subunit Cavα1 contains highly conserved PEST sequences (signals for rapid protein degradation), and in-frame deletion of these PEST sequences results in increased Cavα1 protein levels. Our findings show that Akt-dependent phosphorylation of Cavβ2, the LTCC chaperone for Cavα1, antagonizes Cavα1 protein degradation by preventing Cavα1 PEST sequence recognition, leading to increased LTCC density and the consequent modulation of Ca2+channel function. This novel mechanism by which Akt modulates LTCC stability could profoundly influence cardiac myo- cyte Ca2+entry, Ca2+handling, and contractility. © 2009 Catalucci et al.