Abstract
We investigated the expression of alpha1 and beta subunits of the L-type Ca2+ channel on the protein level in cardiac preparations from normal human heart ventricles and from the hypertrophied septum of patients with hypertrophic obstructive cardiomyopathy (HOCM). 1,4-Dihydropyridine (DHP) binding and immunorecognition by polyclonal antibodies directed against the C-terminal amino acid sequences of the beta2 and beta3 subunits were used for detection and quantification of alpha1, beta2, and beta3 subunits. Bmax of high-affinity DHP binding was 35 +/- 2 fmol/mg protein in HOCM and 20 +/- 2 fmol/mg protein in normal human hearts (P<0.05). In rabbit hearts the anti-beta2 subunit antibody immunoprecipitated 80% of the total amount of DHP-labeled Ca2+ channels present in the assay. Under identical experimental conditions 25% of labeled Ca2+ channels were recovered in the immunoprecipitates of both normal and HOCM ventricles. A similar partial immunoprecipitation was observed in pig hearts. Immunoblot analysis demonstrated that the beta2 subunit was associated with the DHP receptor/Ca2+ channel in cardiac muscle of rabbit, pig, and human heart. In neither of these purified cardiac Ca2+ channels was the beta3 subunit isoform detected. Our results suggest that both alpha1 and beta2 subunit expression is upregulated in HOCM in a coordinate manner.
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