Compartmentalization of calmodulin and tubulin in the male C57BL/6J mouse brain: heterogeneity of age changes in calmodulin compartments.

Calmodulin (CaM) and tubulin were analyzed by radioimmunoassay in subcellular fractions prepared from cerebral cortex and striatum of aging male C57BL/6J mice. Three fractions were prepared by a new procedure: cytosol (soluble); EGTA-releasable, membrane-bound; and detergent-extractable (Triton X-100), membrane-bound fractions. CaM concentration in all three fractions prepared from striatum showed small (10-15%, p less than 0.05) decreases with age (3-31 months). Cortical CaM concentrations were less affected by age, and only the EGTA-releasable fraction decreased. To compare functional activity and immunoreactivity of CaM, soluble CaM was also assayed by the activation of cyclic nucleotide phosphodiesterase (PDE). The radioimmunoassay and PDE activation assays gave equivalent results, suggesting that no alteration occurred with age in biological activity of CaM, via post-translational modification or other mechanisms. Soluble and particulate tubulin concentration did not change significantly with age in either brain region. The changes observed in striatal CaM, particularly in membrane-bound compartments, could contribute to the age-related decline in mammalian basal ganglial function.