DIFFERENTIATION-DEPENDENT EXPRESSION OF CARDIAC DELTA-CAMKII ISOFORMS

Despite their important role in controlling the cardiac Ca2+ homeostas is, presence and functions of individual isoforms of the multifunction al Ca2+/calmodulin-dependent protein kinase in the heart are not well studied. Here we report on expression of isoforms of the delta class i n two differentiation states of the embryonic rat heart-derived cell l ine H9c2 compared to adult rat heart. Reverse transcription coupled po lymerase chain reaction analysis revealed specific expression patterns of four variants of the delta class (delta(Br), delta(C), delta(4), d elta(9)) in adult rat heart, H9c2 myoblasts, and skeletal muscle-like H9c2 myotubes. delta(C) was identified as a common isoform with higher amounts in H9c2 cells and the prominent one in myoblasts. In contrast , expression of delta(9) accompanied cardiac as well as skeletal muscl e differentiation. Expression of delta(B), however, was representative for differentiated cardiac muscle, whereas delta(4) expression coinci ded with differentiation into the skeletal muscle-like state. Our resu lts demonstrate differentiation-dependent isoform expression of the de lta class of the multifunctional Ca2+/calmodulin-dependent protein kin ase of muscle. The identification of cardiac target proteins for this kinase, e.g. the alpha(1)-subunit of the L-type Ca2+ channel, the sarc oplasmic reticulum Ca2+-ATPase, phospholamban and the ryanodine recept or define H9c2 myoblasts as a suitable model system for further functi onal characterization of the identified cardiac delta isoforms. (C) 19 98 Wiley-Liss, Inc.