Mechanisms of Hypotonicity-Induced Calcium Signaling and Integrin Activation by Arachidonic Acid-Derived Inflammatory Mediators in B Cells

Abstract

We previously characterized the initial steps in the activation of novel (calcium-permeant) nonselective cation channels (NSCCs) and calcium release-activated calcium channels in primary murine B lymphocytes. Phospholipase C products, namely diacylglycerol and d-myo-inositol 1,4,5-trisphosphate, were identified as proximal intracellular agonists of these respective channels following mechanical stimulation of B cells. However, neither the distal steps in NSCC activation nor the contribution of these channels to sustained mechanical signaling were defined in these previous studies. In this study, single cell measurements of intracellular Ca2+ were used to define the mechanisms of NSCC activation and demonstrate a requirement for arachidonic acid liberated from diacylglycerol. Several arachidonic acid-derived derivatives were identified that trigger Ca2+ entry into B cells, including the lipoxygenase product 5-hydroperoxyeicosatetranenoic acid and the cytochrome P450 hydroxylase product 20-hydroxyeicosatetraenoic; however, the cytochrome P450 epoxygenase product 5,6-epoxyeicosatrienoic acid is primarily responsible for hypotonicity-induced responses. In addition to regulating calcium entry, our data suggest that eicosanoid-activated NSCCs have a separate and direct role in regulating the avidity of integrins on B cells for extracellular matrix proteins, including ICAM-1 and VCAM-1. Thus, in addition to defining a novel osmotically activated signal transduction pathway in B cells, our results have broad implications for understanding how inflammatory mediators dynamically and rapidly regulate B cell adhesion and trafficking.

Arachidonic acid-induced activation of large-conductance potassium channels and membrane hyperpolarization in mouse B cells

“…The AA-induced K + current could not be found in these studies because they used Cs-methanesulfonate pipette solution for the wholecell patch clamp experiments [21,41]. Partly consistent with these papers, AA-activated cationic conductance was also found in mouse B cell lines (Fig.…”

“…Therefore, persistent K + efflux and strong hyperpolarization by AA might play a role in the PLA 2 -dependent apoptosis of immature B cells. However, apart from the autologous generation by PLA 2 intrinsic to immature B cells, AA can be released from inflammatory tissues and splenic B cells under mechanical stimuli [41]. In this study, we found that LK bg and their activation by AA are often observed in the B220 + /AA4.1 + subset of splenic B cells (immature B cells) whereas not in the B220 + /AA4.1 − subgroup (mature B cells, Fig.…”

“…According to literature, in mouse splenic B cells, AA and its metabolites (e.g., epoxyeicosanoids) activate NSC channels and depolarize mouse splenic B cells [41], which are allegedly mediated by an activation of TRPV or TRPC channels [21]. The AA-induced K + current could not be found in these studies because they used Cs-methanesulfonate pipette solution for the wholecell patch clamp experiments [21,41].…”

Calcium signalling and cell-fate choice in B cells

“…Other channels potentially found in B cells include other TRPC members, various members of the transient receptor potential-vanilloid receptor-1-related (TRPV) family 88,89 , TRPM2 and TRPM7 [90][91][92] , and undefined stretch-activated ion channels and eicosanoid-activated channels [93][94][95] . In addition, convincing evidence for expression of mRNA for splice variants of α-subunits of classic voltage-operated Ca 2+ channels has been reported in B cells and T cells, although electrophysiological evidence of voltage-operated Ca 2+ currents is lacking, suggesting that these splice variants may not be voltage-operated, but instead must have alternative gating mechanisms [96][97][98] .…”

Cerebral Autoregulation in Hypertension and Ischemic Stroke: A Mini Review

“…A higher level of 20-HETE promotes inflammation by the production of Reactive Oxygen Species (ROS) and Nuclear Factor kappa-B (NF-kB) in the cerebral vasculature [66]. It also increases cytokines production and expression of adhesion molecules Intercellular Adhesion Molecule 1 (ICAM-1) and Vascular Cell Adhesion Protein 1 (VCAM-1) on B-lymphocytes [67,68] and endothelial cells [69,70] which further promotes margination of macrophages and enhancing inflammatory cascade. Functional genetic variants in CYP4F2 and CYP4A11 that decrease the formation of 20-HETE are linked to hypertension [71,72] and stroke [19,20,73].…”