Acidic NAADP-sensitive Calcium Stores in the Endothelium

Abstract

Accumulating evidence implicates nicotinic acid adenine dinucleotide phosphate (NAADP) in the control of Ca2؉ -dependent functions. Little, however, is known concerning its role in the vascular endothelium, a major regulator of blood pressure. Here, we show that NAADP acetoxymethyl ester (NAADP-AM), a cell-permeant NAADP analog, increases cytosolic Ca 2؉ concentration in aortic endothelial cells. We demonstrate that these signals and those evoked by acetylcholine are blocked by disrupting acidic organelles with bafilomycin A1. In contrast, Ca 2؉ signals in response to thrombin are only partially inhibited by bafilomycin A1 treatment, and those to ATP were insensitive, suggesting that recruitment of acidic stores is agonist-specific. We further show that NAADP-evoked Ca 2؉ signals hyperpolarize endothelial cells and generate NO. Additionally, we demonstrate that NAADP dilates aortic rings in an endothelium-and NO-dependent manner. Finally, we show that intravenous administration of NAADP-AM into anesthetized rats decreases mean arterial pressure. Our data extend the actions of NAADP to the endothelium both in vitro and in vivo, pointing to a previously unrecognized role for this messenger in controlling blood pressure.Nicotinic acid adenine dinucleotide phosphate (NAADP) 4 is a potent and widespread Ca 2ϩ -mobilizing messenger first described in sea urchin eggs (1, 2). Although its mechanism of action is subject to debate, much evidence indicates that NAADP mobilizes Ca 2ϩ from acidic, lysosome-like organelles (3) through activation of novel Ca 2ϩ -permeable channels (1, 4). These channels have recently been identified as members of the two-pore channel family (5-9). Importantly, mobilization of so-called "acidic Ca 2ϩ stores" (10) by NAADP is often linked to mobilization of the well established endoplasmic reticulum Ca 2ϩ stores through the process of Ca 2ϩ -induced Ca 2ϩ release (11). NAADP is thus thought to act as trigger during agonistevoked Ca 2ϩ signaling (2). The functional positioning of NAADP-sensitive Ca 2ϩ stores upstream of those targeted by the messengers, inositol 1,4,5-trisphosphate (IP 3 ) and cyclic ADP-ribose, raises the possibility that agonist-evoked Ca 2ϩ signals previously ascribed to endoplasmic reticulum Ca 2ϩ release might also involve NAADP and acidic organelles.Using isolated cells or tissues, NAADP-induced Ca 2ϩ signaling has been implicated in the regulation of several physiological functions such as egg fertilization (12, 13), T lymphocyte activation (14), muscle contraction (15), and neuronal differentiation (16). The role of NAADP in vivo, however is not known, although a recent study demonstrated that a newly described NAADP antagonist could prevent T cell motility in an animal model of multiple sclerosis (17).In the cardiovascular system, a role for NAADP has been demonstrated in agonist-evoked Ca 2ϩ signaling in pulmonary (15, 18) and coronary arteries (19,20), cardiac myocytes (21), and the renal microcirculation (22). Direct measurements of NAADP have confirmed its messenge...

Two-pore channel 1 interacts with citron kinase, regulating completion of cytokinesis

“…3,4,7 In plants, studies of Ca 2C release in Arabidopsis identified AtTPC1 as a channel 8 that mediates the slow vacuolar current, 9 regulating germination and stomatal movement. 10 TPCs have been shown to regulate differentiation, 11 smooth muscle contraction 12 and endothelial cell activation, 13 consistent with previous studies implicating nicotinic acid adenine dinucleotide phosphate (NAADP)-induced Ca 2C release in these events, [14][15][16] and supported by several overexpression, knockdown and knockout models. 3,4,6,17 Regulation and affinity of TPC ion channels is a contentious issue.…”

Differential Activation of Cultured Neonatal Cardiomyocytes by Plasmalemmal Versus Intracellular G Protein-coupled Receptor 55

“…However, the Ca 2ϩ response pattern was strikingly different in the two paradigms. Extracellular administration of LPI resulted in a relatively slow response that reached a peak within 1-2 min and continued with a plateau phase, whereas LPI microinjection induced a fast and transitory effect similar to that reported upon activation of other intracellular GPCRs, such as those for angiotensin II (29,33,62) or endothelin 1 (28). We have noticed likewise discrepancies in the plasmalemmal-initiated versus intracellularly initiated Ca 2ϩ responses by the G protein-coupled estrogen receptor GPER/GPR30 (34,63), which is reportedly expressed at both sites (64,65).…”

“…Measurement of Membrane Potential-The relative changes in membrane potential of single cardiomyocytes were evaluated using bis-(1,3-dibutylbarbituric acid) trimethine oxonol, bis-(1,3-dibutylbarbituric acid) trimethine oxonol, a slow-response, voltage-sensitive dye, as described previously (32)(33)(34). Upon membrane hyperpolarization, the dye concentrates in the cell membrane, leading to a decrease in fluorescence intensity, whereas depolarization induces the sequestration of the dye into the cytosol, resulting in an increase of the fluorescence intensity (35).…”

Regulation of Ion Channels by Pyridine Nucleotides

“…115 In endothelial cells, NAADP + has been recognized as an essential mediator of histamine-induced secretion of von Willebrand factor 116 and a regulator of nitric oxide production. 117 On the basis of the observation that intravenous administration of a cell permanent NAADPester lowers blood pressure in rats, it has been suggested that NAADP + regulates systemic blood pressure. 117 …”

“…117 On the basis of the observation that intravenous administration of a cell permanent NAADPester lowers blood pressure in rats, it has been suggested that NAADP + regulates systemic blood pressure. 117 …”