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      Calmodulin Stimulation of Plasmalemmal Ca 2+-Pump of Canine Aortic Smooth Muscle

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          Abstract

          Plasma-membrane-enriched fractions of canine aortic smooth muscle possess an ATP-supported Ca<sup>2+</sup> accumulation which has an absolute requirement for Mg<sup>2+</sup> and a high affinity for Ca<sup>2+</sup> (Km ∼ 0.5 µM). The rate of ATP-supported Ca<sup>2+</sup> transport is not affected by several calmodulin antagonists, but is stimulated by exogenously added calmodulin. The maximal effect of calmodulin on the rate of ATP-dependent Ca<sup>2+</sup> transport (at 5.0 µM Ca<sup>2+</sup>) occurs at 10 µg/ml calmodulin and represents an approximately 3-fold stimulation. This calmodulin stimulation of Ca<sup>2+</sup> transport does not require pretreatment of the membranes by EGTA and is an intrinsic property of the plasma membranes. A high-affinity Ca<sup>2+</sup>-ATPase (K<sub>m</sub> for Ca<sup>2+</sup> ∼0.5 µM) is also present in the aortic smooth muscle plasma membrane. This high-affinity Ca<sup>2+</sup>-ATPase does not require Mg<sup>2+</sup> for catalytic activity, but is in fact inhibited by increasing Mg<sup>2+</sup> concentrations. Calmodulin at concentrations effective for the stimulation of the ATP-dependent Ca<sup>2+</sup> transport has no effect on the high-affinity Ca<sup>2+</sup>-ATPase activity or on the basal ATPase activity stimulated by 5 mM Mg<sup>2+</sup> or Ca<sup>2+</sup>. Our results indicate that isolated plasma membranes of canine aortic smooth muscle contain no endogenous calmodulin. The ability of exogenously added calmodulin to stimulate the rate of ATP-dependent Ca<sup>2+</sup> transport by vascular smooth muscle plasma membranes suggests that calmodulin may play a role in lowering the cytoplasmic concentration of ionized calcium during vasodilatation. An Mg<sup>2+</sup>-independent, but not an Mg<sup>2+</sup>-dependent high-affinity Ca<sup>2+</sup>-ATPase, was identified in the plasma membranes. This may be separate from the plasmalemmal Ca<sup>2+</sup>-pump.

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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
          1986
          1986
          23 September 2008
          : 23
          : 1
          : 22-33
          Affiliations
          aSmooth Muscle Research Program, Department of Neurosciences, McMaster University Health Sciences Center, Hamilton, Canada; bCenler for Molecular Nutrition, Georgetown University Medical Center. Washington, D.C., USA
          Article
          158622 Blood Vessels 1986;23:22–33
          10.1159/000158622
          © 1986 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
          Pages: 12
          Categories
          Research Paper

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