The development of extraocular muscle calcium homeostasis parallels visuomotor system maturation.
Extraocular muscle is modulated by unique genetic and epigenetic factors to produce an atypical phenotype. As a prelude to regulation studies, we characterized the development of cation homeostasis in the predominately fast-twitch extraocular muscles. By atomic absorption spectroscopy, total muscle calcium content declined from birth to postnatal day 27 and, thereafter, stabilized at a low level in limb but increased dramatically in extraocular muscle (to 40x limb values). By ELISA, the slow isoform of sarcoplasmic reticulum Ca2+-ATPase predominated in neonatal eye muscle, but subsequently was largely replaced by the fast isoform. This replacement in eye muscle was completed later than in limb. Residual, slow Ca2+-ATPase likely resides in an unusual slow tonic fiber type characteristic of eye muscle. Maturation of the definitive extraocular muscle Ca2+-ATPase pattern paralleled myofiber Ca2+ and sarcoplasmic reticulum content. These data show that, like myosin heavy chain expression patterns, the development of cation homeostatic mechanisms in extraocular muscle parallels landmarks in the maturation of vision and eye movement control systems. Findings suggest that cation homeostasis in extraocular muscle may be susceptible to perturbations of the developing visual sensory system, as we have previously shown for myosin.
Porter
J D
JD
Departments of Ophthalmology, Neurology, and Neuroscience, University Hospitals of Cleveland and Case Western Reserve University, 11100 Euclid Avenue, Cleveland, Ohio, 44106-5068, USA. jdp7@po.cwru.edu
Karathanasis
P
P
D000375:Aging; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002412:Cations / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D006614:Hindlimb; D006706:Homeostasis; D007527:Isoenzymes / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism; D024510:Muscle Development; D018656:Muscle Fibers, Fast-Twitch / Q000201:enzymology / Q000378:metabolism; D018657:Muscle Fibers, Slow-Twitch / Q000201:enzymology / Q000378:metabolism; D018482:Muscle, Skeletal / Q000201:enzymology / Q000378:metabolism; D009801:Oculomotor Muscles / Q000201:enzymology / Q000254:growth & development* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012519:Sarcoplasmic Reticulum / Q000201:enzymology; D013054:Spectrophotometry, Atomic
D002412:Cations; D007527:Isoenzymes; D000252:Calcium-Transporting ATPases; D008274:Magnesium; D002118:Calcium