Zymosan-induced release of inositol phosphates at resting cytosolic Ca2+ concentrations in macrophages

Abstract

Hydrolysis of polyphosphoinositides by phosphodiesterase has been demonstrated to be involved in the control of cytosolic Ca2+ concentrations. The stimulation of Ca2+ ionophores of the release of inositol phosphates in macrophages, and other cells, together with the Ca2+ requirements for zymosan-induced phospholipase C activation, make unclear the relationship between Ca2+ mobilization and polyphosphoinositide hydrolysis. The results in the present paper strongly suggest that, for zymosan-induced phospholipase C activation, a previous increase in cytosolic Ca2+ is not a required event. These results also show that zymosan-activated release of inositol phosphates may be mediated by a guanine-nucleotide-binding protein.

Prostaglandin release but not superoxide production by rat Kupffer cells stimulated in vitro depends on Na+/H+ exchange

“…While phorbol esters are known to activate protein kinase C 171, zymosan was found to stimulate transiently the adenylate cyclase activity of rat Kupffer cells [l] as well as phospholipase C in alveolar [30] and peritoneal [31] macrophages. Thus, a reaction common to both signal transductions en route to an increased prostaglandin synthesis is the obvious target for the Na+/H +-exchange-dependent activation.…”

Receptor-mediated phagocytosis in human neutrophils is associated with increased formation of inositol phosphates and diacylglycerol. Elevation in cytosolic free calcium and formation of inositol phosphates can be dissociated from accumulation of diacylglycerol.

“…The aim of the present study was to investigate initially whether ingestion of IgG-or C3bi-opsonized yeast particles by human neutrophils is associated with an increased formation of inositol phosphates, as recently demonstrated in macrophages (10) and diacylglycerol, but more importantly, whether these second messengers play a role in the control of phagocytosis in these cells.…”

Ca2+-induced changes in the secondary structure of a 60 kDa phosphoinositide-specific phospholipase C from bovine brain cytosol

“…In this regard it has to be borne in mind that, once cells are disrupted and cytosolic and membrane fractions separated, two sorts of PLC activities can be detected: membrane-bound and cytosolic. In membranes, a receptor-activatable activity exists which is stimulated in the presence of GTP or its non-hydrolysable analogues [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. By using exogenous substrate a cytosolic activity can be detected which hydrolyses Ptdlns in a Ca2"-dependent fashion [27][28][29].…”

“…In membranes, a receptor-activatable activity exists which is stimulated in the presence of GTP or its non-hydrolysable analogues [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. By using exogenous substrate a cytosolic activity can be detected which hydrolyses Ptdlns in a Ca2"-dependent fashion [27][28][29]. The phosphodiesteratic breakdown of PtdInsP2 by cytosolic activity is also stimulated by Ca2' and membrane destabilization [27,30].…”

“…By using exogenous substrate a cytosolic activity can be detected which hydrolyses Ptdlns in a Ca2"-dependent fashion [27][28][29]. The phosphodiesteratic breakdown of PtdInsP2 by cytosolic activity is also stimulated by Ca2' and membrane destabilization [27,30]. More recently it has been reported that cytosolic PLC activity can be stimulated to attack PtdInsP2, but not Ptdlns, by GTP and its nonhydrolysable analogues [31][32][33][34].…”