Mechanisms of Intracellular Calcium Movement Activated by Guanine Nucleotides and Inositol-1,4,5-Trisphosphate
It is now well established that the intracellular second messenger inositol-1,4,5-trisphosphate (IP3) is involved in the release of Ca2+ from a Ca2+ -sequestering organelle, widely considered to be the endoplasmic reticulum (ER) (Berridge and Irvine, 1984; Gill, 1985; Majeruset al., 1986). In a series of recent studies, we observed that a highly sensitive and specific guanine nucleotide regulatory process induces a release of Ca2+ in cells that appears very similar to that mediated by IP3(Gillet al., 1986; Uedaet al., 1986; Chueh and Gill, 1986). Our initial studies were conducted using either permeabilized cells or isolated microsomal membrane vesicles derived from the NIE-115 neuronal cell line; GTP-dependent Ca2+ release was observed to be very similar in the two preparations (Gillet al., 1986; Uedaet al., 1986). Recent studies (Henne and Söling, 1986; Jean and Klee, 1986; Chuehet al., 1987) have extended the number of diverse cell types in which the same GTP-activated Ca2+ release process is observed. In each cell type, submicromolar GTP concentrations rapidly effect a substantial release of Ca2+ sequestered via internal Ca2+ -pumping activity within a nonmitochondrial organelle, believed to be the ER. The Ca2+ -accumulating properties of this intracellular organelle have been described in detail in earlier studies with permeabilized cells (Gill and Chueh, 1985).
KeywordsGuanine Nucleotide Inositol Trisphosphate Membrane Fusion Event Glioma Hybrid Cell Plasma Membrane Calcium Pump
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