Chronic phosphate depletion (PD) causes a rise in basal level of cytosolic calcium ([Ca2+]i) in rat brain synaptosomes, a decrease in their ATP content and a reduction in Vmax of their Ca2+ ATPase and Na+-K+ ATPase. The chronology of the events that lead to these derangements is not elucidated. The present study examined this issue by evaluating the changes in rat in these parameters in brain synaptosomes during the evolution of PD over a period of 6 weeks. The results show that the initial derangement is a rise in the Vmax of Ca2+ ATPase during the first 2 weeks of PD. This is followed by a rise in [Ca2+]i, a fall in ATP content and decrease in the Vmax of Ca2+ ATPase and Na+-K+ ATPase by the end of the 3 week and most of these derangement worsened during the 4th to 6th weeks of PD. Taken together our data are consistent with the notion that PD is associated with an initial increase in calcium influx into the synaptosomes. This is followed by a modest but significant rise in [Ca2+]i which in turn would inhibit mitochondrial oxidation and ATP generation leading to a decrease in ATP content. The latter compromises the activity of Ca2+ ATPase and Na+-K+ ATPase which are involved, directly or indirectly, in calcium extrusion out of the synaptosomes. The increased entry of calcium combined with decreased calcium extrusion are followed by a further rise in basal levels of [Ca2+]i. This sequence of events continues until a steady state is reached and is characterized by reduced basal ATP content, reduced Vmax of Ca2+ ATPase and Na+-K+ ATPase and elevated basal level of [Ca2+]i.

Keywords:
Ca2+ ATPase, ATP, Cytosolic calcium, Phosphate depletion, Brain synaptosomes
This content is only available via PDF.
© 1994 S. Karger AG, Basel
1994
Copyright / Drug Dosage / Disclaimer
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.
You do not currently have access to this content.