Abstract

The effects of different ionic media on Ca 2+ uptake and release in isolated brain microsomes were investigated. KCl (100 mM) provided the best medium for Ca 2+ uptake in the presence of ATP. The effect of myo-inositol 1,4,5-trisphosphate (IP 3) on Ca 2+ release was examined and was maximum at 0.2 μM. IP 3-induced Ca 2+ release was dependenton extramicrosomal free Ca 2+ concentration with maximal release at 5.0 μM free Ca 2+. Replacement of KCl by sucrose or NaCl did not show any response to IP 3. Electron microscopy showed that the microsomal fraction consisted of characteristic endoplasmic reticulum-derived vesicular profiles and were free of mitochondria or plasma membrane contamination. Our results support the concept that the endoplasmic reticulum is the target for IP 3-induced mobilization of Ca 2+ in the cell.

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