Ca++ regulation in caffeine-derived microplasmodia of Physarum polycephalum.

Caffeine-derived microplasmodia possess a Ca++-sequestering system which can initiate motility. The experiments presented here suggest that this system is membranous and nonmitochondrial in nature. Therefore, it is proposed that the shuttle streaming in the plasmodium is controlled by the localized release and uptake of free Ca++ from an intracellular storage system analogous to the sarcoplasmic reticulum.