Inositol 1,4,5-trisphosphate receptor in developing and senescent rat cerebellum

Numerous process associated with intracellular calcium homeostasis have previously been found to vary with age. To determine whether the binding sites for the calcium-mobilizing second messenger, inositol 1,4,5-trisphosphate (InsP3), also displays such variation, [3H]InsP3 binding was investigated in cerebellar or cerebral cortical membranes prepared from rats at different ages from birth up to 24 months of age. In the cerebellum, the InsP3 receptor density was very low during the first week after birth, increased markedly between days 8 and 28 and then reached an apparent plateau between 28 to 56 days of age. The InsP3 receptor binding affinity was comparable at different developmental stages. No age-related differences were found in InsP3 receptor density or affinity in the cerebral cortex of 3-, 6-, 9-, 12-, and 24-month-old rats. In the cerebellum, InsP3 receptor density but not affinity was significantly reduced in 24-month-old compared only to 3-month-old animals. Our data suggest that the changes in InsP3 receptor binding during early development might reflect the growth and maturation of neurons containing these receptors (i.e., Purkinje cells). Furthermore, the age-dependent reduction in InsP3 receptor density, together with the recent report of senescent changes in protein kinase C activity, indicate that disruption of phosphoinositide second messenger system may be of importance to the impairment of neuronal responsiveness and behavioral deficits observed with aging.