Calsequestrin, a component of the inositol 1,4,5-trisphosphate-sensitive Ca2+ store of chicken cerebellum

The presence and distribution of calsequestrin (CS), Ca2+ pump, and inositol 1,4,5-trisphosphate (IP3) receptor were investigated biochemically and immunologically in microsomal (P3) fractions isolated from chicken cerebrum and cerebellum. Two different batches of polyclonal antibodies specific for chicken skeletal muscle CS identified a Ca2+ binding, CS-like protein that was extremely enriched in cerebellum P3 fractions and absent from all cerebrum fractions. The cerebellum CS-like protein was deemed authentic CS because the N-terminal amino acid domain and peptide mapping were identical to those of skeletal muscle CS in the same species. CS was detected in striated muscles and cerebellum only. Cerebellum P3 fractions were also found to be considerably enriched in Ca2+ pump and IP3 receptor compared with the homologous cerebrum fractions, as judged by measurements of Ca2+ uptake, Ca2(+)-ATPase activity, IP3-induced Ca2+ release, and [3H]IP3 binding, respectively. Cerebellum microsomal fractions therefore appear to contain membrane fragments endowed with Ca2+ pump, IP3 receptor, and CS, i.e., three key components of a Ca2+ storage organelle.