Modulation of two functionally distinct Ca 2+ stores in astrocytes: Role of the plasmalemmal Na/Ca exchanger

Modulation of two functionally distinct Ca 2+ stores in astrocytes: Role of the plasmalemmal... Mechanisms that regulate the amount of releasable Ca2+ in intracellular stores of cultured mouse astrocytes were investigated using digital imaging of fura‐2 loaded cells. At rest, the cytoplasmic Ca2+ concentration, (Ca2+)cyt, was about 110 nM. In the absence of extracellular Ca2+, cyclopiazonic acid (CPA), an inhibitor of the endoplasmic reticulum (ER) Ca2+‐ATPase, induced a transient, four‐fold increase in (Ca2+)cyt due to the release of Ca2+ from inositol triphosphate (IP3) sensitive stores. Caffeine (CAF), which releases Ca2+ from Ca2+‐sensitive stores, induced a two‐fold increase in (Ca2+)cyt. The CPA‐ and CAF‐sensitive stores could be released independently. Changes in the amplitudes of the Ca2+ transients were taken as a measure of changes in store content. Removal of extracellular Na+ or addition of ouabain, which inhibit Ca2+ extrusion and promote Ca2+ entry across the plasmalemma via the Na/Ca exchanger, caused minimal increases in resting (Ca2+)cyt but greatly potentiated both CPA‐ and CAF‐induced Ca2+ transients. The amount of Ca2+ releasable from the IP3 (CPA) sensitive store was directly proportional to cytosolic Na+ concentration (i.e., inversely proportional to the transmembrane Na+ electrochemical gradient). Under these reduced Na+ gradient conditions, little, if any, Ca2+ destined for the ER stores enters the cells through voltage‐dependent Ca2+ channels. These results demonstrate that mouse astrocytes contain two distinct ER Ca2+ stores, the larger, IP3‐ (CPA‐) sensitive, and the smaller, Ca2+‐ (CAF‐) sensitive. The Ca2+ content of both ER stores can be regulated by the Na/Ca exchanger. Thus, the magnitude of cellular responses to signals that are mediated by Ca2+ release induced by the two second messengers, IP3 and Ca2+, can be modulated by factors that affect the net transport of Ca2+ across the plasmalemma. © 1996 Wiley‐Liss, Inc. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Glia Wiley

Modulation of two functionally distinct Ca 2+ stores in astrocytes: Role of the plasmalemmal Na/Ca exchanger

Loading next page...
 
/lp/wiley/modulation-of-two-functionally-distinct-ca-2-stores-in-astrocytes-role-EYuQwfcEtO
Publisher
Wiley
Copyright
Copyright © 1996 Wiley‐Liss, Inc.
ISSN
0894-1491
eISSN
1098-1136
DOI
10.1002/(SICI)1098-1136(199604)16:4<296::AID-GLIA2>3.0.CO;2-Z
Publisher site
See Article on Publisher Site

Abstract

Mechanisms that regulate the amount of releasable Ca2+ in intracellular stores of cultured mouse astrocytes were investigated using digital imaging of fura‐2 loaded cells. At rest, the cytoplasmic Ca2+ concentration, (Ca2+)cyt, was about 110 nM. In the absence of extracellular Ca2+, cyclopiazonic acid (CPA), an inhibitor of the endoplasmic reticulum (ER) Ca2+‐ATPase, induced a transient, four‐fold increase in (Ca2+)cyt due to the release of Ca2+ from inositol triphosphate (IP3) sensitive stores. Caffeine (CAF), which releases Ca2+ from Ca2+‐sensitive stores, induced a two‐fold increase in (Ca2+)cyt. The CPA‐ and CAF‐sensitive stores could be released independently. Changes in the amplitudes of the Ca2+ transients were taken as a measure of changes in store content. Removal of extracellular Na+ or addition of ouabain, which inhibit Ca2+ extrusion and promote Ca2+ entry across the plasmalemma via the Na/Ca exchanger, caused minimal increases in resting (Ca2+)cyt but greatly potentiated both CPA‐ and CAF‐induced Ca2+ transients. The amount of Ca2+ releasable from the IP3 (CPA) sensitive store was directly proportional to cytosolic Na+ concentration (i.e., inversely proportional to the transmembrane Na+ electrochemical gradient). Under these reduced Na+ gradient conditions, little, if any, Ca2+ destined for the ER stores enters the cells through voltage‐dependent Ca2+ channels. These results demonstrate that mouse astrocytes contain two distinct ER Ca2+ stores, the larger, IP3‐ (CPA‐) sensitive, and the smaller, Ca2+‐ (CAF‐) sensitive. The Ca2+ content of both ER stores can be regulated by the Na/Ca exchanger. Thus, the magnitude of cellular responses to signals that are mediated by Ca2+ release induced by the two second messengers, IP3 and Ca2+, can be modulated by factors that affect the net transport of Ca2+ across the plasmalemma. © 1996 Wiley‐Liss, Inc.

Journal

GliaWiley

Published: Apr 1, 1996

References

You’re reading a free preview. Subscribe to read the entire article.


DeepDyve is your
personal research library

It’s your single place to instantly
discover and read the research
that matters to you.

Enjoy affordable access to
over 18 million articles from more than
15,000 peer-reviewed journals.

All for just $49/month

Explore the DeepDyve Library

Search

Query the DeepDyve database, plus search all of PubMed and Google Scholar seamlessly

Organize

Save any article or search result from DeepDyve, PubMed, and Google Scholar... all in one place.

Access

Get unlimited, online access to over 18 million full-text articles from more than 15,000 scientific journals.

Your journals are on DeepDyve

Read from thousands of the leading scholarly journals from SpringerNature, Elsevier, Wiley-Blackwell, Oxford University Press and more.

All the latest content is available, no embargo periods.

See the journals in your area

DeepDyve

Freelancer

DeepDyve

Pro

Price

FREE

$49/month
$360/year

Save searches from
Google Scholar,
PubMed

Create folders to
organize your research

Export folders, citations

Read DeepDyve articles

Abstract access only

Unlimited access to over
18 million full-text articles

Print

20 pages / month

PDF Discount

20% off