Ontogeny of the GTP-Binding Protein Goin Rat Brain and Heart

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Abstract
We determined the ontogeny of the GTP-binding protein Go in rat brain and heart by employing highly sensitive enzyme immunoassay methods. In the brain, the .alpha. subunit of Go (Go.alpha.) gradually increased and reached adult levels approximately 20 and 30 days after birth in cerebral cortex and cerebellum, respectively. Concentrations of .beta. subunits, which were also quantified by the immunoassay, were almost equal to those of Go.alpha. in the brain of rats younger than 10 days, but were higher than those of Go.alpha. after 10 days. These results suggest the late development of GTP-binding proteins other than Go. Go.alpha. was immunohistochemically positive in neuropils and negative in cell bodies at any age tested. In the heart, the concentrations of Go.alpha. increased up to several times of the adult level just after birth, and then gradually decreased after the 20th postnal day. The level of Go.alpha. in the liver, however, was very low and constant throughout ontogenic development. An immunohistochemical study indicated that Go.alpha. was positive in the cardiac muscle of young rat, but negative in that of adult rat. These results indicate that Go.alpha. exists in cells other than those of nervous tissues and neuroendocrine cells in some periods of ontogenic development.