EXPRESSION OF CALCIUM-CHANNEL SUBUNITS IN THE NORMAL AND DISEASED HUMAN MYOCARDIUM

We investigated the expression of alpha(1) and beta subunits of the L- type Ca2+ channel on the protein level in cardiac preparations from no rmal human heart ventricles and from the hypertrophied septum of patie nts with hypertrophic obstructive cardiomyopathy (HOCM). 1,4-Dihydropy ridine (DHP) binding and immunorecognition by polyclonal antibodies di rected against the C-terminal amino acid sequences of the beta(2) and beta(3) subunits were used for detection and quantification of alpha(1 ), beta(2) and beta(3) subunits. B-max of high-affinity DHP binding wa s 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-beta(2) subunit antib ody immunoprecipitated 80% of the total amount of DHP-labeled Ca2+ cha nnels 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 immunoprecipitatio n was observed in pig hearts. Immunoblot analysis demonstrated that th e beta(2) subunit was associated with the DHP receptor/Ca2+ channel in cardiac muscle of rabbit, pig, and human heart. In neither of these p urified cardiac Ca2+ channels was the beta(3) subunit isoform detected . Our results suggest that both alpha(1) and beta(2) subunit expressio n is upregulated in HOCM in a coordinate manner.