The involvement of the cytoskeleton in regulating IP₃ receptor‐mediated internal Ca²⁺ release in human blood platelets.

Abstract

In this study we have used saponin to permeabilize platelet membranes in order to test directly the involvement of IP3 in regulating internal Ca2+ release, and to measure IP3 binding to its receptor. Our results indicate that platelet vesicles release Ca2+ as early as 3 seconds after IP3 addition. Using [3H]IP3, we have found that platelets contain a single class of high affinity IP3 binding sites with a Kd of approximately 0.20 (+/- 0.01) nM. Immuno-blotting shows that platelets contain a 260 kDa polypeptide which shares immunological cross reactivity with brain IP3 receptor. Immunofluorescence staining data indicate that the IP3 receptor is preferentially located at the periphery of the platelet plasma membrane. Most importantly, both IP3 binding and IP3-induced Ca2+ release activities are significantly inhibited by cytochalasin D (a microfilament inhibitor) and colchicine (a microtubule inhibitor). These findings suggest that the cytoskeleton is involved in the regulation of IP3 binding and IP3 receptor-mediated Ca2+ release during platelet activation.

Inositol (1,4,5)-trisphosphate receptor links to filamentous actin are important for generating local Ca2+ signals in pancreatic acinar cells

“…In this study it was shown that local Ca 2+ spiking depends on the microtubular network to position the ER locally, and therefore Ca 2+ release sites, within the apical region of pancreatic acinar cells (Fogarty et al, 2000b). Evidence from studies performed in a variety of cell types, including pancreatic cells, suggests that IP 3 Rs link to the actin cytoskeleton and actin-associated proteins (Bourguignon et al, 1993a;Giovannucci et al, 2000;Joseph and Samanta, 1993;Rossier et al, 1991;Sugiyama et al, 2000;Tuvia et al, 1999). Furthermore, it has been shown that disrupting the actin cytoskeleton with actin depolymerising agents, impairs the ability of cells to raise cytosolic Ca 2+ levels in response to (Bourguignon et al, 1993b;Shin et al, 2000).…”

Inositol Trisphosphate Receptor Ca2+Release Channels

“…In neurons, a protein 4.1N-InsP 3 R complex may be associated with cytoskeletal elements enriched in postsynaptic compartments (301). It has been widely observed that disruption of the actin filament network has profound effects on InsP 3 -evoked Ca 2ϩ signals (56,387,484,503). Actin plays a role in the translational mobility of InsP 3 R-1 (148) but not InsP 3 R-3 (132, 148).…”

Hyaluronan-mediated CD44 activation of RhoGTPase signaling and cytoskeleton function promotes tumor progression

“…Ankyrin also binds to intracellular Ca 2+ channels such as the inositol 1,4,5 trisphosphate (IP 3 ) receptor. Most importantly, ankyrin binding to IP 3 receptors is known to modulate IP 3 binding and Ca 2+ activity [36,[42][43][44]. In addition, ankyrin is involved in regulating the subcellular location of IP 3 receptors [45].…”