Expression of Ca2+/calmodulin-dependent protein kinase II δ-subunit isoforms in rats with hypertensive cardiac hypertrophy

Myocardial hypertrophy is characterized by abnormal intracellular Ca2+ handling and decreased contractile performance. Ca2+/calmodulin-dependent protein kinase II (CaMKII) phosphorylates numerous Ca2+ handling proteins and thus can regulate intracellular Ca2+ homeostasis directly. We therefore investigated whether differential expression of CaMKII isoforms occurs with cardiac hypertrophy which might promote an abnormal intracellular Ca2+ homeostasis. We further investigated the potential influence of angiotensin (Ang) II on CaMKII expression levels. Hearts from adult Spontaneously Hypertensive Rats (SHR) and hearts from two transgenic rat models with Ang II-dependent hypertension were studied. The expression of the cardiac CaMKII isoforms delta (2), delta (3), delta (4) and delta (9) was determined by RT-PCR and immunoblot methods. Rats transgenic for the mouse Ren-2 gene (mrTGR), SHR and controls were studied at the age of 6 months and rats transgenic for the human renin-angiotensin system (hrTGR) from postnatal day 1 to week 8. SHR and mrTGR had an increased heart/body weight ratio (26 and 25%) compared with controls (p < 0.05). SHR hearts showed significantly increased mRNA levels of delta (4) and delta (9) (p < 0.05) with no change for delta (2) and delta (3). mrTGR hearts had a significantly increased delta (4) and a significantly decreased delta (3) transcript level (p < 0.05) with no change for delta (2) and delta (9). hrTGR hearts developed severe hypertrophy (42%) after postnatal day 14. The neonatal delta (2), delta (3) and delta (4) isoform expression levels were higher (30-100%) compared with SD controls. The levels decreased with increasing age and equalized to controls at week 8, except for delta (4) which started to increase after week 4 (p < 0.05). CaMKII delta protein levels of all cardiac hypertrophy models were increased in sarcoplasmic reticulum preparations (50-120%) compared with controls (p < 0.05) while the cytosolic levels remained unchanged. Thus, CaMKII delta isoforms are differentially expressed in cardiac hypertrophy. The fetal delta (4) isoform was constantly expressed. CaMKII delta adopts the fetal phenotype independent of the type of hypertrophic stimulus. The observed alterations of CaMKII delta isoform patterns may affect intracellular Ca2+ homeostasis and thus contribute to the abnormal contractile phenotype of cardiac hypertrophy.