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      Mechanism of Non-Capacitative Ca 2+ Influx in Response to Bradykinin in Vascular Endothelial Cells

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          Abstract

          Bradykinin is a potent vasoactive nonapeptide. It elicits a rise in cytosolic Ca<sup>2+</sup> (Ca<sup>2+</sup>)<sub>i</sub> in endothelial cells, resulting in Ca<sup>2+</sup>-dependent synthesis and release of endothelial vasodilators. In the present study, we investigated the mechanism of bradykinin-induced Ca<sup>2+</sup> influx in primary cultured rat aortic endothelial cells and in a mouse heart microvessel endothelial cell line (H5V). Bradykinin-induced Ca<sup>2+</sup> influx was resolved into capacitative Ca<sup>2+</sup> entry (CCE) and non-CCE. The non-CCE component was inhibited by a B2 receptor antagonist (HOE140; 1 µ M) and a phospholipase C (PLC) inhibitor (U73122; 10 µ M). The action of bradykinin could be mimicked by 1-oleoyl-2-acetyl-glycerol, an analogue of diacylglycerol (DAG), and by RHC80267, a DAG-lipase inhibitor. Immunoblots showed that TRPC6 was one of the main TRPC channels expressed in endothelial cells. Transfection of H5V cells with two siRNA constructs against TRPC6 both markedly reduced the TRPC6 protein level and, at the same time, decreased the percentage of cells displaying bradykinin-induced non-CCE. siRNA transfection also reduced the magnitude of non-CCE among the cells responding to bradykinin. Taken together, our data suggest that bradykinin-induced non-CCE is mediated via the B2-PLC pathway, and that DAG may be involved in this process. Further, TRPC6 is one of the important channels participating in bradykinin-induced non-CCE in endothelial cells.

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          Most cited references 21

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          Store-operated calcium channels.

          In electrically nonexcitable cells, Ca(2+) influx is essential for regulating a host of kinetically distinct processes involving exocytosis, enzyme control, gene regulation, cell growth and proliferation, and apoptosis. The major Ca(2+) entry pathway in these cells is the store-operated one, in which the emptying of intracellular Ca(2+) stores activates Ca(2+) influx (store-operated Ca(2+) entry, or capacitative Ca(2+) entry). Several biophysically distinct store-operated currents have been reported, but the best characterized is the Ca(2+) release-activated Ca(2+) current, I(CRAC). Although it was initially considered to function only in nonexcitable cells, growing evidence now points towards a central role for I(CRAC)-like currents in excitable cells too. In spite of intense research, the signal that relays the store Ca(2+) content to CRAC channels in the plasma membrane, as well as the molecular identity of the Ca(2+) sensor within the stores, remains elusive. Resolution of these issues would be greatly helped by the identification of the CRAC channel gene. In some systems, evidence suggests that store-operated channels might be related to TRP homologs, although no consensus has yet been reached. Better understood are mechanisms that inactivate store-operated entry and hence control the overall duration of Ca(2+) entry. Recent work has revealed a central role for mitochondria in the regulation of I(CRAC), and this is particularly prominent under physiological conditions. I(CRAC) therefore represents a dynamic interplay between endoplasmic reticulum, mitochondria, and plasma membrane. In this review, we describe the key electrophysiological features of I(CRAC) and other store-operated Ca(2+) currents and how they are regulated, and we consider recent advances that have shed insight into the molecular mechanisms involved in this ubiquitous and vital Ca(2+) entry pathway.
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            Direct activation of human TRPC6 and TRPC3 channels by diacylglycerol.

            Eukaryotic cells respond to many hormones and neurotransmitters with increased activity of the enzyme phospholipase C and a subsequent rise in the concentration of intracellular free calcium ([Ca2+]i). The increase in [Ca2+]i occurs as a result of the release of Ca2+ from intracellular stores and an influx of Ca2+ through the plasma membrane; this influx of Ca2+ may or may not be store-dependent. Drosophila transient receptor potential (TRP) proteins and some mammalian homologues (TRPC proteins) are thought to mediate capacitative Ca2+ entry. Here we describe the molecular mechanism of store-depletion-independent activation of a subfamily of mammalian TRPC channels. We find that hTRPC6 is a non-selective cation channel that is activated by diacylglycerol in a membrane-delimited fashion, independently of protein kinases C activated by diacylglycerol. Although hTRPC3, the closest structural relative of hTRPC6, is activated in the same way, TRPCs 1, 4 and 5 and the vanilloid receptor subtype 1 are unresponsive to the lipid mediator. Thus, hTRPC3 and hTRPC6 represent the first members of a new functional family of second-messenger-operated cation channels, which are activated by diacylglycerol.
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              Recent developments in vascular endothelial cell transient receptor potential channels.

              Among the 28 identified and unique mammalian TRP (transient receptor potential) channel isoforms, at least 19 are expressed in vascular endothelial cells. These channels appear to participate in a diverse range of vascular functions, including control of vascular tone, regulation of vascular permeability, mechanosensing, secretion, angiogenesis, endothelial cell proliferation, and endothelial cell apoptosis and death. Malfunction of these channels may result in disorders of the human cardiovascular system. All TRP channels, except for TRPM4 and TRPM5, are cation channels that allow Ca2+ influx. However, there is a daunting diversity in the mode of activation and regulation in each case. Specific TRP channels may be activated by different stimuli such as vasoactive agents, oxidative stress, mechanical stimuli, and heat. TRP channels may then transform these stimuli into changes in the cytosolic Ca2+, which are eventually coupled to various vascular responses. Evidence has been provided to suggest the involvement of at least the following TRP channels in vascular function: TRPC1, TRPC4, TRPC6, and TRPV1 in the control of vascular permeability; TRPC4, TRPV1, and TRPV4 in the regulation of vascular tone; TRPC4 in hypoxia-induced vascular remodeling; and TRPC3, TRPC4, and TRPM2 in oxidative stress-induced responses. However, in spite of the large body of data available, the functional role of many endothelial TRP channels is still poorly understood. Elucidating the mechanisms regulating the different endothelial TRP channels, and the associated development of drugs selectively to target the different isoforms, as a means to treat cardiovascular disease should, therefore, be a high priority.
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                Author and article information

                Journal
                JVR
                J Vasc Res
                10.1159/issn.1018-1172
                Journal of Vascular Research
                S. Karger AG
                1018-1172
                1423-0135
                2006
                July 2006
                28 July 2006
                : 43
                : 4
                : 367-376
                Affiliations
                aLi Ka Shing Institute of Health Sciences, Faculty of Medicine, and Departments of bPhysiology and cBiochemistry, Chinese University of Hong Kong, Hong Kong, SAR, China
                Article
                94096 J Vasc Res 2006;43:367–376
                10.1159/000094096
                16791008
                © 2006 S. Karger AG, Basel

                Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

                Page count
                Figures: 8, References: 31, Pages: 10
                Categories
                Research Paper

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