Identification of Giant Isoforms of Obscurin in Rat Striated Muscles Using Polyclonal Antibodies

Using produced polyclonal antibodies specific to the N-terminal sequence (residues 61-298) of rat obscurin, we investigated the isoform composition of this protein in 4 striated muscles: myocardium of the left ventricle, diaphragm, skeletal m. gastrocnemius (containing mainly fast fibers), and m. soleus (containing mainly slow fibers). The m. gastrocnemius, m. soleus, and diaphragm were found to have 2 giant isoforms of obscurin: a smaller A-isoform and a larger B-isoform. Their molecular weights were ~870 and ~1150 kDa in the diaphragm and m. gastrocnemius and ~880 and ~1130 kDa in m. soleus, respectively. The B-isoform to A-isoform ratio was 1:3 in the diaphragm and m. soleus and 1:4 in the m. gastrocnemius. In the left-ventricular myocardium, A-isoform of obscurin with a molecular weight of ~880 kDa was found. No other obscurin isoforms or their fragments within the molecular weight range of 10 up to ~800 kDa were revealed in the investigated rat striated muscles. The antibodies produced are recommended for research into qualitative and quantitative changes of giant obscurin isoforms in rat striated muscles in the norm and during the development of pathological processes.