Go, a GTP‐Binding Protein: Immunochemical and Immunohistochemical Localization in the Rat

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Abstract
The tissue and cellular distribution of a GTP-binding protein, Go, was investigated in the rat by immunochemical and immunohistochemical methods. Because the specific antibody for the .alpha. subunit of bovine Go (Go.alpha.) cross-reacted with rat Go.alpha., and enzyme immunoassay method developed for bovine Go.alpha. was applied for measuring the tissue concentration of Go.alpha. in the rat. Go.alpha. was detected in all tissues examined except blood cells. The concentration of Go.alpha. was highest in the CNS (.apprx. 7.7 and 4.4 nmol/g in the cerebrum, respectively), followed by the pituitary gland and sciatic nerve. Among the other peripheral tissues, relatively high concentrations of Go.alpha. were observed in the urinary bladder, stomach and intestines; however, these values were > 2% of the concentration in the cerebrum. Go.alpha. in the intestine was located mostly in the muscle layer. Immunohistochemical study showed that Go.alpha. was associated mostly with the neural elements but not with cells particular to each peripheral organ. Go.alpha. was also present in the membranes of neuroendocrine cells, including glandular cells in the anterior lobe of the pituitary gland, chromaffin cells in the medulla of the adrenal gland, islets cells in the pancreas, and parafollicular cells in the thyroid. These results indicate that Go is localized exclusively in the nervous tissues and neuroendocrine cells.