Physical and Functional Interaction Between Calcineurin and the Cardiac L-Type Ca Channel

The L-type Ca channel (LTCC) is the major mediator of Ca influx in cardiomyocytes, leading to both mechanical contraction and activation of signaling cascades. Among these Ca -activated cascades is calcineurin, a protein phosphatase that promotes hypertrophic growth of the heart. Coimmunoprecipitations from heart extracts and pulldowns using heterologously expressed proteins provided evidence for direct binding of calcineurin at both the N and C termini of 11.2. At the C terminus, calcineurin bound specifically at amino acids 1943 to 1971, adjacent to a well-characterized protein kinase (PK)A/PKC/PKG phospho-acceptor site Ser1928. In vitro assays demonstrated that calcineurin can dephosphorylate 11.2. Channel function was increased in voltage-clamp recordings of ICa,L from cultured cardiomyocytes expressing constitutively active calcineurin, consistent with previous observations in cardiac hypertrophy in vivo. Conversely, acute suppression of calcineurin pharmacologically or with specific peptides decreased ICa,L. These data reveal direct physical interaction between the LTCC and calcineurin in heart. Furthermore, they demonstrate that calcineurin induces robust increases in ICa,L and highlight calcineurin as a key modulator of pathological electrical remodeling in cardiac hypertrophy. (Circ Res. 2009;105:51-60.)