Document Detail

The relation of Vmax to INa, GNa, and h infinity in a model of the cardiac Purkinje fiber.
MedLine Citation:
PMID:  262397     Owner:  NLM     Status:  MEDLINE    
The inward sodium current in cardiac muscle is difficult to study by voltage clamp methods, so various indirect experimental measures have been used to obtain insight into its characteristics. These methods depend on the relationship between maximal upstroke velocity of the action potential (Vmax) and the sodium current (INa), usually defined in terms of the Hodgkin-Huxley model. These relationships were explored using an adaptation of this model to cardiac Purkinje fibers. In general Vmax corresponded to INa, and it could be used to determine the relationship of membrane potential to GNa, and h infinity. The results, however, depended on the method of stimulation of the action potential, and an optimal stimulation method was determined. A commonly used experimental technique called "membrane responsiveness" was shown to distort seriously the properties of steady-state gating inactivation that is supposed to measure. Estimation of the changes in maximal sodium conductance, such as those produced by tetrodotoxin (TTX), would be accurately measured. Some experimental results have indicated a voltage-dependent effect of TTX. Characteristics of the measures of TTX effect under those conditions were illustrated. In summary, calculations with a model of the cardiac Purkinje fiber action potential provide insight into the accuracy of certain experimental methods using maximal upstroke velocity as a measure of INa, and cast doubt on other experimental methods, such as membrane responsiveness.
M Walton; H A Fozzard
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Biophysical journal     Volume:  25     ISSN:  0006-3495     ISO Abbreviation:  Biophys. J.     Publication Date:  1979 Mar 
Date Detail:
Created Date:  1981-10-29     Completed Date:  1981-10-29     Revised Date:  2009-11-18    
Medline Journal Info:
Nlm Unique ID:  0370626     Medline TA:  Biophys J     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  407-20     Citation Subset:  IM    
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MeSH Terms
Action Potentials
Heart / physiology*
Heart Conduction System / physiology*
Membrane Potentials
Models, Biological
Purkinje Fibers / physiology*
Sodium / metabolism
Grant Support
Reg. No./Substance:

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