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 char acterized the development of cation homeostasis in the predominately fast-t witch extraocular muscles. By atomic absorption spectroscopy, total muscle calcium content declined from birth to postnatal day 27 and, thereafter, st abilized at a low level in limb but increased dramatically in extraocular m uscle (to 40x limb values). By ELISA, the slow isoform of sarcoplasmic reti culum Ca2+-ATPase predominated in neonatal eye muscle, but subsequently was largely replaced by the fast isoform, This replacement in eye muscle was c ompleted later than in limb. Residual, slow Ca2+-ATPase likely resides in a n 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 mech anisms in extraocular muscle parallels landmarks in the maturation of visio n and eye movement control systems. Findings suggest that cation homeostasi s in extraocular muscle may be susceptible to perturbations of the developi ng visual sensory system, as we have previously shown for myosin. (C) 1999 Academic Press.