Developmental changes in isoform expression of Ca2+/calmodulin-dependent protein kinase II delta-subunit in rat heart

In the heart, Ca2+/calmodulin-dependent protein kinase II is critically inv olved in the regulation of Ca2+ homeostasis. Previously the predominant exp ression of a subclass of Ca2+/calmodulin-dependent protein kinase II delta- subunit, containing a second variable domain, was demonstrated in cardiac t issue. Here we report on the expression pattern of the non-neuronal members of this delta-subunit subclass, delta(2), delta(3), delta(4), and delta(9) in the developing heart of the rat. By semiquantitative RT-PCR isoform del ta(3) was shown to be typically expressed in the heart, whereas delta(4) wa s expressed in skeletal muscle of adult rat. From embryonic day 14 up to th e adult state of rat ventricular muscle, amounts of delta(9) transcripts re mained unchanged, transcript levels of isoforms delta(2) and delta(3) were significantly increased, whereas level of delta(4) transcript was significa ntly decreased. Immunoblotting, using an antibody recognizing specifically these delta-isoforms containing the second variable domain, revealed three separated protein signals at about 59 kDa, 58 kDa, and 56 kDa. The immunore action at about 59 kDa, corresponding to the predicted molecular mass of de lta(4), was dramatically diminished, whereas a significant increase in the signal at about 58 kDa was assumed to represent an increase in isoform delt a(3). The protein signal at about 56 kDa, close to the predicted molecular mass of isoform delta(2), was high in the embryonic heart and significantly decreased after birth. Our data suggest the predominant expression of isof orm delta(2) in the embryonic heart, establish delta(3) to be the typical i soform in the adult heart and define the skeletal muscle form delta(4) to b e characteristic for fetal and neonatal stages of the heart. J. Cell. Bioch em. 74:202-210, 1999. (C) 1999 Wiley-Liss, Inc.