Physical and functional interaction between calcineurin and the cardiac L-Type Ca²⁺ Channel

The L-type Ca²⁺ channel (LTCC) is the major mediator of Ca ²⁺ influx in cardiomyocytes, leading to both mechanical contraction and activation of signaling cascades. Among these Ca²⁺-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 α₁1.2. 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 α₁1.2. Channel function was increased in voltage-clamp recordings of I_Ca,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 I_Ca,L. These data reveal direct physical interaction between the LTCC and calcineurin in heart. Furthermore, they demonstrate that calcineurin induces robust increases in I_Ca,L and highlight calcineurin as a key modulator of pathological electrical remodeling in cardiac hypertrophy.