Document Detail

Structural alterations in cardiac calcium release units resulting from overexpression of junctin.
MedLine Citation:
PMID:  11162129     Owner:  NLM     Status:  MEDLINE    
Junctin is a 26 kDa membrane protein that binds to calsequestrin, triadin, and ryanodine receptors (RyRs) within the junctional sarcoplasmic reticulum of calcium release units. The sequence of junctin includes a short N-terminal cytoplasmic domain a single transmembrane domain, and a highly charged C-terminal domain located in the sarcoplasmic reticulum lumen. Dog and mouse junctins are highly conserved at the transmembrane domains, but the luminal domains are more divergent. To probe the contribution of junctin to the architecture of calcium release units in heart, we engineered transgenic mice overexpressing canine junctin and examined the left ventricular myocardium by electron microscopy. Overall architecture of calcium release units is similar in control myocardium and in myocardium overexpressing junctin by 5-10-fold. In both myocardia, junctional SR cisternae are closely associated with exterior membranes (plasmalemma and transverse tubules). The cisternae are flat; they contain a string of calsequestrin beads and are lined by a row of feet, or RyRs, on the side facing the exterior membranes. T tubule surface density, measured as the perimeter of T tubule profiles v area of section, is the same in transgenic and control myocardia (305 v 289 nm/nm(2)). Three changes affecting the junctional SR architecture are apparent in the myocardium overexpressing junctin. One is a more tightly zippered appearance of the junctional SR cisternae. The width of the junctional SR is narrower and less variable in overexpressing than in control myocardium and the calsequestrin content is more compact. A second change is the extension of zippered junctional SR domains to non-junctional regions, which we term "frustrated" junctional SR. A third change is an increase in the extent of association between SR and T tubules. In junctin overexpressing myocardium junctional SR cisternae cover approximately 45% of the surface of all T tubule profiles, while in control myocardium the coverage approximately 30%. Junctional associations between SR and T tubules are increased in size. We conclude that the increase in junctin expression affects the packing of calsequestrin in the junctional SR and facilitates the association of SR and T tubules.
L Zhang; C Franzini-Armstrong; V Ramesh; L R Jones
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Journal of molecular and cellular cardiology     Volume:  33     ISSN:  0022-2828     ISO Abbreviation:  J. Mol. Cell. Cardiol.     Publication Date:  2001 Feb 
Date Detail:
Created Date:  2001-02-22     Completed Date:  2001-04-26     Revised Date:  2007-11-14    
Medline Journal Info:
Nlm Unique ID:  0262322     Medline TA:  J Mol Cell Cardiol     Country:  England    
Other Details:
Languages:  eng     Pagination:  233-47     Citation Subset:  IM    
Copyright Information:
Copyright 2001 Academic Press.
Department of Medicine, Indiana University School of Medicine, Indianapolis, IN 46202, USA.
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MeSH Terms
Amino Acid Sequence
Calcium / metabolism*
Calcium-Binding Proteins*
Calsequestrin / metabolism
Carrier Proteins / metabolism*
Cloning, Molecular
DNA, Complementary / metabolism
Heart / drug effects*
Membrane Proteins*
Mice, Transgenic
Microscopy, Electron
Microsomes / metabolism
Mixed Function Oxygenases*
Molecular Sequence Data
Muscle Proteins / metabolism*
Myocardium / metabolism*,  ultrastructure
Sarcoplasmic Reticulum / ultrastructure
Sequence Homology, Amino Acid
Ventricular Function, Left / drug effects
Grant Support
Reg. No./Substance:
0/Calcium-Binding Proteins; 0/Calsequestrin; 0/Carrier Proteins; 0/DNA, Complementary; 0/Membrane Proteins; 0/Muscle Proteins; 7440-70-2/Calcium; EC 1.-/Asph protein, mouse; EC 1.-/Mixed Function Oxygenases

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