Calcium and Hormone Action

107

Annexin V belongs to a family of proteins that interact with phospholipids in a Ca 2؉ -dependent manner. This protein has been demonstrated to have anti-phospholipase A 2 activity. However, this effect has never yet been reported with the 85-kDa cytosolic PLA 2 (cPLA 2 ). We studied, in a model of differentiated and streptolysin O-permeabilized HL-60 cells, the effect of annexin V on cPLA 2 activity after stimulation by calcium, GTP␥S (guanosine 5-O-(3-thiotriphosphate)), formyl-Met-LeuPhe, or phorbol 12-myristate 13-acetate. Both recombinant and human placental purified annexin V inhibit cPLA 2 activity whatever the stimulus used. The decrease of arachidonic acid release is of 40 and 50%, respectively, at [Ca 2؉ ] of 3 and 10 M. The mechanism of inhibition was also analyzed. cPLA 2 requires calcium and protein kinase C (PKC) or mitogen-activated protein kinase phosphorylation for its activation. As annexin V was shown to be an endogenous inhibitor of PKC, PKC-stimulated cPLA 2 activity was analyzed. Using GF109203x, a specific PKC inhibitor, we demonstrated that this pathway is of minor importance in our model. cPLA 2 inhibition by annexin V is not linked to PKC inhibition. To test the hypothesis of phospholipid depletion, mutants of annexin V were constructed using mutagenesis directed to Ca 2؉ site. We demonstrate that the Ca 2؉ site located in domain I is necessary for the inhibitory effect of annexin V on cPLA 2 activity. The site in domain IV is also involved but with less efficiency. In contrast, mutations in site II and III do not modify this effect. Moreover, annexin V mutated on all sites does not inhibit cPLA 2 . Thus, we propose a predominant role of module (I/IV) in the biological action of annexin V, which, in physiological conditions, may control cPLA 2 activity by depletion of the phospholipid substrate.

Section: Discussionmentioning

confidence: 99%

Section: Release Of [ 3 H]arachidonic Acid From Slo-permeabilized Hl-mentioning

confidence: 99%

Inhibition of Cytosolic Phospholipase A2 by Annexin V in Differentiated Permeabilized HL-60 Cells

Mira

Dubois

Oudinet

et al. 1997

107

“…The established Ca 2ϩ -releasing messenger IP 3 (9,10) as well as the more recently discovered Ca 2ϩ -liberating agents cyclic ADP-ribose and nicotinic acid adenine dinucleotide phosphate each elicit repetitive cytosolic Ca 2ϩ spikes in the apical pole (2,11,12). Therefore, it has been proposed that messenger(s) generated at the basal membrane in response to agonist stimulation easily diffuse across the cell and release Ca 2ϩ primarily in the apical pole because of the high density of Ca 2ϩ release channels in this part of the cell (2,(13)(14)(15)(16)(17).…”

mentioning

confidence: 99%

Long Distance Communication between Muscarinic Receptors and Ca2+ Release Channels Revealed by Carbachol Uncaging in Cell-attached Patch Pipette

Ashby¹,

Camello-Almaraz²,

Gerasimenko

et al. 2003

We have investigated the characteristics of cytosolic Ca 2؉ signals induced by muscarinic receptor activation of pancreatic acinar cells that reside within intact pancreatic tissue. We show that these cells exhibit global Ca 2؉ waves and local apical Ca 2؉ spikes. This is the first evidence for local Ca 2؉ signaling in undissociated pancreatic tissue. The mechanism of formation of localized Ca 2؉ signals was examined using a novel approach involving photolysis of caged carbachol inside a patch pipette attached to the basal surface of an acinar unit. This local activation of basal muscarinic receptors elicited local cytosolic Ca 2؉ spikes in the apical pole more than 15 m away from the site of stimulation. In some experiments, local basal receptor activation elicited a Ca 2؉ wave that started in the apical pole and then spread toward the base. Currently, there are two competing hypotheses for preferential apical Ca 2؉ signaling. One invokes the need for structural proximity of the cholinergic receptors and the Ca 2؉ release channels in the apical pole, whereas the other postulates long distance communication between basal receptors and the channels. Our intrapipette uncaging experiments provide definitive evidence for long distance communication between basal muscarinic receptors and apical Ca 2؉ release channels.In response to agonist stimulation, many cell types produce transient elevations in the cytosolic Ca 2ϩ concentration ([Ca 2ϩ ] i ), which remain localized to a specific subcellular domain (1). In isolated pancreatic acinar cells, a low concentration of acetylcholine (ACh) 1 can evoke repetitive local cytosolic Ca 2ϩ spikes, which are confined to the granule containing apical pole (2). These local Ca 2ϩ spikes can activate exocytosis through the apical plasma membrane (3) and open Ca 2ϩ -dependent Cl Ϫ channels present exclusively in the apical plasma membrane, thereby regulating acinar fluid secretion (4).Agonist-receptor interaction causes activation of phospholipase C and the generation of inositol 1,4,5-trisphosphate (IP 3 ), which in turn opens Ca 2ϩ release channels in the endoplasmic reticulum membrane (5), thereby explaining the liberation of Ca 2ϩ from this intracellular store (6). Because the G-protein coupled receptors for cholecystokinin are localized in the basolateral plasma membrane as demonstrated in early autoradiographic studies on intact pancreas (7), the classical view of pancreatic acinar cell stimulation involves the binding of agonist to plasma membrane receptors located at the base. It is this end of the cell that is close to blood vessels and pancreatic nerve terminals from where physiologically released agonists approach the cell (8). If agonist-receptor interaction occurs at the base and Ca 2ϩ release occurs at the opposite (apical) pole, there is a need for a long distance Ca 2ϩ -releasing intracellular messenger. The established Ca 2ϩ -releasing messenger IP 3 (9, 10) as well as the more recently discovered Ca 2ϩ -liberating agents cyclic ADP-ribose and nicotinic acid adeni...

“…In one study clear localization of type 3 IP 3 R (IP 3 R3) in the LP has been reported (13). Propagation of the Ca 2ϩ wave from the LP to the BP was suggested to occur through a series of Ca 2ϩ -induced Ca 2ϩ release events mediated by the ryanodine receptor (RyR) (5,14). Accordingly, it was reported that cADPR, an activator of the RyR (15), releases Ca 2ϩ from the IS of pancreatic acini (16).…”

mentioning

confidence: 99%

Polarized Expression of Ca2+ Channels in Pancreatic and Salivary Gland Cells

Lee¹,

Xu²,

Zeng³

et al. 1997

265

200

In polarized epithelial cells [Ca 2؉ ] i waves are initiated in discrete regions and propagate through the cytosol. The structural basis for these compartmentalized and coordinated events are not well understood. In the present study we used a combination of [Ca 2؉ ] i imaging at high temporal resolution, recording of Ca 2؉ -activated Cl ؊ current, and immunolocalization by confocal microscopy to study the correlation between initiation and propagation of [Ca 2؉ ] i waves and localization of Ca 2؉ release channels in pancreatic acini and submandibular acinar and duct cells. In all cells Ca 2؉ waves are initiated in the luminal pole and propagate through the cell periphery to the basal pole. All three cell types express the three known inositol 1,4,5-trisphosphate receptors (IP 3 Rs). Expression of IP 3 Rs was confined to the area just underneath the luminal and lateral membranes, with no detectable receptors in the basal pole or other regions of the cells. In pancreatic acini and SMG ducts IP 3 R3 was also found in the nuclear envelope. Expression of ryanodine receptor was detected in submandibular salivary gland cells but not pancreatic acini. Accordingly, cyclic ADP ribose was very effective in mobilizing Ca 2؉ from internal stores of submandibular salivary gland but not pancreatic acinar cells. Measurement of [Ca 2؉ ] i and localization of IP 3 Rs in the same cells suggests that only a small part of IP 3 Rs participate in the initiation of the Ca 2؉ wave, whereas most receptors in the cell periphery probably facilitate the propagation of the Ca 2؉ wave. The combined results together with our previous studies on this subject lead us to conclude that the internal Ca 2؉ pool is highly compartmentalized and that compartmentalization is achieved in part by polarized expression of Ca 2؉ channels.