Localization of calmodulin in rat tissues.

The localization of calmodulin, a calcium-dependent modulator of many enzymes, was studied in rat liver, skeletal muscle, and adrenal slices. Calmodulin is found in liver cytoplasm, nucleus, and plasma membrane. Much of the cytoplasmic calmodulin is associated with glycogen particles presumably bound to enzymes involved in glycogen metabolism. Skeletal muscle calmodulin is found on the I-band, also associated with glycogen particles. Intermyofibrillar staining that is not glycogen associated is also observed. Calmodulin is localized in the cytoplasm and nucleus of adrenal cortex cells. Injection of corticotropin leads to a greatly increased localization of calmodulin in nuclei of the adrenal cortex. These observations suggest that one role of calmodulin may be the regulation of hormone effects on nuclear processes.