Spatially and Functionally Distinct Ca ²⁺ Stores in Sarcoplasmic and Endoplasmic Reticulum

TLDR

The organization of calcium stores in the sarcoplasmic and endoplasmic reticulum (S‑ER) is poorly understood. High‑resolution imaging of intact astrocytes and arterial myocytes was used to study calcium storage and release dynamics in the S‑ER. The S‑ER forms a continuous tubular network yet its calcium stores are partitioned into small, spatially distinct compartments that act as discrete units, with different inhibitors and physiological agonists selectively unloading separate compartments, indicating that cells can generate spatially and temporally distinct calcium signals to regulate specific calcium‑dependent processes.

Abstract

The organization of calcium (Ca 2+ ) stores in the sarcoplasmic and endoplasmic reticulum (S-ER) is poorly understood. The dynamics of the storage and release of calcium in the S-ER of intact, cultured astrocytes and arterial myocytes were studied with high-resolution imaging methods. The S-ER appeared to be a continuous tubular network; nevertheless, calcium stores in the S-ER were organized into small, spatially distinct compartments that functioned as discrete units. Cyclopiazonic acid (an inhibitor of the calcium pump in the S-ER membrane) and caffeine or ryanodine unloaded different, spatially separate compartments. Heterogeneity of calcium stores was also revealed in cells activated by physiological agonists. These results suggest that cells can generate spatially and temporally distinct calcium signals to control individual calcium-dependent processes.