Document Detail

Inhibition of the activation and troponin calcium binding of dog cardiac myofibrils by acidic pH.
MedLine Citation:
PMID:  6235979     Owner:  NLM     Status:  MEDLINE    
The aim of experiments described here was to test whether deactivation of cardiac myofibrils in acidic pH is associated with decreases in amounts of calcium bound to myofilament troponin. We determined the amounts of myofibrillar bound calcium attributable to troponin, from measurements of calcium binding to myofibrils and to myosin and from determination of the troponin C content of the myofibrillar preparations (0.40 nmol troponin C/mg protein). In measurements done at 2 mM free magnesium, 2 mM (magnesium-adenosine triphosphate, ionic strength 0.12, 22 degrees C, the pCa50 (-log of the half maximally activating molar free calcium) for myofibrillar magnesium-adenosine triphosphatase activity was 5.87 at pH 7.0, 5.49 at pH 6.5, and 5.04 at pH 6.2. This change in calcium sensitivity of myofibrillar magnesium-adenosine triphosphatase activity was present whether or not ethyleneglycol-bis(beta-aminoethyl ether)-N, N'-tetraacetic acid, was used to buffer the free calcium and whether or not myofibrillar troponin I had been phosphorylated by cyclic adenosine 3',5'-monophosphate-dependent protein kinase. However, the change in pCa50 of myofibrillar adenosine triphosphatase activity induced by acidic pH, was greater when free magnesium was reduced from 2.0 to 0.05 mM, and less when free magnesium was increased from 2.0 mM to 10 and 15 mM. The change in pCa50 with acidic pH was less if the ionic strength was reduced from 0.12 to 0.035 M. The magnesium-adenosine triphosphatase activity of troponin/tropomyosin-free myofibrils was independent of pCa and unaffected by a reduction of pH from 7.0 to 6.5. The affinity of myofibrillar troponin C for calcium decreased as pH was reduced from 7.0 to 6.5 and to 6.2 with and without ethyleneglycolbis(beta-aminoethyl ether)-N,N'-tetraacetic acid, and in a manner predicted from the effect of acidic pH on pCa50 for myofibrillar activation. Our results are consistent with the idea that at least part of the mechanism responsible for deactivation of the adenosine triphosphatase activity of cardiac myofilaments in acidic pH is a reduction in the affinity of myofibrillar troponin C for calcium.
E M Blanchard; R J Solaro
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Publication Detail:
Type:  In Vitro; Journal Article; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Circulation research     Volume:  55     ISSN:  0009-7330     ISO Abbreviation:  Circ. Res.     Publication Date:  1984 Sep 
Date Detail:
Created Date:  1984-10-25     Completed Date:  1984-10-25     Revised Date:  2009-11-19    
Medline Journal Info:
Nlm Unique ID:  0047103     Medline TA:  Circ Res     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  382-91     Citation Subset:  IM    
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MeSH Terms
Adenosine Triphosphatases / metabolism
Adenosine Triphosphate / metabolism
Calcium / metabolism*
Egtazic Acid
Electrophoresis, Polyacrylamide Gel
Hydrogen-Ion Concentration
Myocardium / enzymology,  metabolism*
Myofibrils / physiology*
Myosins / metabolism
Troponin / metabolism*
Grant Support
Reg. No./Substance:
0/Troponin; 56-65-5/Adenosine Triphosphate; 67-42-5/Egtazic Acid; 7440-70-2/Calcium; EC 3.6.1.-/Adenosine Triphosphatases; EC

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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