Document Detail

A steady-state mechanism can account for the properties of inositol 2,4,5-trisphosphate-stimulated Ca2+ release from permeabilized L1210 cells.
MedLine Citation:
PMID:  8382056     Owner:  NLM     Status:  MEDLINE    
We have investigated the effects of sub-maximal Ins(2,4,5)P3 concentrations on the Ca2+ permeability of the residual undischarged Ca2+ stores in electroporated or digitonin-permeabilized L1210 cells by measuring Ca(2+)-efflux rate after addition of the ATPase inhibitor thapsigargin. Low concentrations of Ins(2,4,5)P3, causing rapid discharge of a small proportion of the releasable Ca2+, result in a substantial stimulation of Ca2+ efflux after thapsigargin addition. This indicates firstly that in the absence of thapsigargin there must have been a substantial, counterbalancing, increase in rate of Ca2+ pumping, and secondly that the increased Ca2+ permeability is more consistent with a steady state than with a quantal model of Ca2+ release. Similar increases in passive Ca2+ permeability are produced by addition of concentrations of ionomycin which produce equivalent changes in Ca2+ loading to those produced by Ins(2,4,5)P3, although the time course and initial rate of Ca2+ release are very much slower. In the presence of a Ca(2+)-buffering system, the time course of Ca2+ release by Ins(2,4,5)P3 becomes superimposable on that of ionomycin, indicating that the initial rapid phase of Ins(2,4,5)P3-stimulated Ca2+ is at least partially due to positive feedback from extravesicular Ca2+.
J W Loomis-Husselbee; A P Dawson
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  The Biochemical journal     Volume:  289 ( Pt 3)     ISSN:  0264-6021     ISO Abbreviation:  Biochem. J.     Publication Date:  1993 Feb 
Date Detail:
Created Date:  1993-03-18     Completed Date:  1993-03-18     Revised Date:  2009-11-18    
Medline Journal Info:
Nlm Unique ID:  2984726R     Medline TA:  Biochem J     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  861-6     Citation Subset:  IM    
School of Biological Sciences, University of East Anglia, Norwich, U.K.
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MeSH Terms
Aniline Compounds
Biological Transport, Active
Calcium / pharmacokinetics*
Calcium-Transporting ATPases / antagonists & inhibitors,  physiology*
Cell Membrane Permeability
Inositol Phosphates / pharmacology*
Ionomycin / pharmacology
Leukemia L1210 / metabolism*
Models, Biological
Terpenes / pharmacology
Reg. No./Substance:
0/Aniline Compounds; 0/Buffers; 0/Inositol Phosphates; 0/Terpenes; 0/Xanthenes; 121714-13-4/Fluo-3; 56092-81-0/Ionomycin; 67526-95-8/Thapsigargin; 7440-70-2/Calcium; 91840-07-2/inositol 2,4,5-trisphosphate; EC ATPases

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