The M lines are structural landmarks in striated muscles, necessary for sarcomeric stability and as anchoring sites for the M isoform of @entity908 kinase ( @entity48959 ). These structures, especially prominent in fast skeletal muscles, are missing in rodent extraocular muscle, a particularly fast and active muscle group. In this study, we tested the hypotheses that 1). myomesin and M protein (cytoskeletal components of the M lines) and @entity48959 are downregulated in @entity19 extraocular muscle compared with the leg muscles, gastrocnemius and soleus; and 2). the expression of other cytosolic and mitochondrial CK isoforms is correspondingly increased. As expected, @entity19 extraocular muscles expressed lower levels of myomesin, M protein, and @entity48959 mRNA than the leg muscles. Immunocytochemically, myomesin and M protein were not detected in the banding pattern typically seen in other skeletal muscles. Surprisingly, message abundance for the other known CK isoforms was also lower in the extraocular muscles. Moreover, total CK activity was significantly decreased compared with that in the leg muscles. Based on these data, we reject our second hypothesis and propose that other energy-buffering systems may be more important in the extraocular muscles. The downregulation of major structural and metabolic elements and relative overexpression of two @entity1920 kinase isoforms suggest that the extraocular muscle group copes with its functional requirements by using strategies not seen in typical skeletal muscles.

Paradoxical absence of M lines and downregulation of XXXX kinase in @entity19 extraocular muscle.

@entity19 :: ('10090', 'Species') :: ['mouse'] @entity908 :: ('MESH:D003401', 'Chemical') :: ['creatine'] @entity1920 :: ('CHEBI:16027', 'Chemical') :: ['adenylate'] @entity48959 :: ('12715(Tax:10090)', 'Gene') :: ['CK-M']
@entity908 :: (MESH:D003401,Chemical) :: ['creatine']
