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

Abstract

We explored a potential structural and functional link between filamentous actin (F-actin) and inositol (1,4,5)-trisphosphate receptors (IP3Rs) in mouse pancreatic acinar cells. Using immunocytochemistry, F-actin and type 2 and 3 IP3Rs (IP3R2 and IP3R3) were identified in a cellular compartment immediately beneath the apical plasma membrane. In an effort to demonstrate that IP3R distribution is dependent on an intact F-actin network in the apical subplasmalemmal region, cells were treated with the actin-depolymerising agent latrunculin B. Immunocytochemistry indicated that latrunculin B treatment reduced F-actin in the basolateral subplasmalemmal compartment, and reduced and fractured F-actin in the apical subplasmalemmal compartment. This latrunculin-B-induced loss of F-actin in the apical region coincided with a reduction in IP3R2 and IP3R3, with the remaining IP3Rs localized with the remaining F-actin. Experiments using western blot analysis showed that IP3R3s are resistant to extraction by detergents, which indicates a potential interaction with the cytoskeleton. Latrunculin B treatment in whole-cell patch-clamped cells inhibited Ca2+-dependent Cl– current spikes evoked by inositol (2,4,5)-trisphosphate; this is due to an inhibition of the underlying local Ca2+ signal. Based on these findings, we suggest that IP3Rs form links with F-actin in the apical domain and that these links are essential for the generation of local Ca2+ spikes.

A broad spectrum of actin paralogs inParamecium tetraureliacells display differential localization and function

“…In related Apicomplexans equivalent structures are also connected by short F-actin strands (Jewett and Sibley, 2003). A similar structure/function effect is discussed for mammalian cells whose cortical Ca 2+ stores may be positioned by F-actin (Rosado and Sage, 2000;Wang et al, 2002;Roderick and Bootman, 2003;Turvey et al, 2005). Although we could not show such an effect in response to cytochalasin in Paramecium (Mohamed et al, 2003), this may be due to the involvement of drug-insensitive isoforms.…”

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).…”

Exocytosis, dependent on Ca2+ release from Ca2+ stores, is regulated by Ca2+ microdomains

“…3206 Journal of Cell Science 123 (18) It is well established that InsP 3 Rs are enriched beneath the apical plasma membrane of polarized epithelia (Lee et al, 1997;Nathanson et al, 1994;Yule et al, 1997); as shown by immunohistochemistry, the receptors colocalize with apical markers such as the F-actin apical web (Waterman-Storer and Salmon, 1998), and tight-junction markers such as ZO-1 (Larina et al, 2007;Turvey et al, 2005). The mechanisms of this localization are not well understood but disruptions of both the microtubular system (Colosetti et al, 2003) and the F-actin network perturb the generation of Ca 2+ signals (Turvey et al, 2005).…”

“…The mechanisms of this localization are not well understood but disruptions of both the microtubular system (Colosetti et al, 2003) and the F-actin network perturb the generation of Ca 2+ signals (Turvey et al, 2005). It has been proposed that the microtubular system acts to position the ER (Fogarty et al, 2000c) and that F-actin is part of a complex that specifically anchors InsP 3 Rs (Foskett et al, 2007).…”