Document Detail

Dual effects of external magnesium on action potential duration in guinea pig ventricular myocytes.
MedLine Citation:
PMID:  7611483     Owner:  NLM     Status:  MEDLINE    
Effects of extracellular magnesium (Mg2+) on action potential duration (APD) and underlying membrane currents in guinea pig ventricular myocytes were studied by using the whole cell patch-clamp method. Increasing external Mg2+ concentration [Mg2+]o) from 0.5 to 3 mM produced a prolongation of APD at 90% repolarization (APD90), whereas 5 and 10 mM Mg2+ shortened it. [Mg2+]o, at 3 mM or higher, suppressed the delayed outward K+ current and the inward rectifier K+ current. Increases in [Mg2+]o depressed the peak amplitude and delayed the decay time course of the Ca2+ current (ICa), the latter effect is probably due to the decrease in Ca(2+)-induced inactivation. Thus 3 mM Mg2+ suppressed the peak ICa but increased the late ICa amplitude at the end of a 200-ms depolarization pulse, whereas 10 mM Mg2+ suppressed both components. Application of 10 mM Mg2+ shifted the voltage-dependent activation and inactivation by approximately 10 mV to more positive voltage due to screening the membrane surface charges. Application of manganese (1-5 mM) also caused dual effects on APD90, similar to those of Mg2+, and suppressed the peak ICa with slowed decay. These results suggest that the dual effects of Mg2+ on APD in guinea pig ventricular myocytes can be, at least in part, explained by its action on ICa with slowed decay time course in addition to suppressive effects on K+ currents.
S Zhang; T Sawanobori; H Adaniya; Y Hirano; M Hiraoka
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Publication Detail:
Type:  Comparative Study; Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  The American journal of physiology     Volume:  268     ISSN:  0002-9513     ISO Abbreviation:  Am. J. Physiol.     Publication Date:  1995 Jun 
Date Detail:
Created Date:  1995-08-14     Completed Date:  1995-08-14     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  0370511     Medline TA:  Am J Physiol     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  H2321-8     Citation Subset:  IM    
Department of Cardiovascular Diseases, Tokyo Medical and Dental University, Japan.
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MeSH Terms
Action Potentials / drug effects*
Barium / pharmacology
Calcium Channels / physiology
Cells, Cultured
Egtazic Acid / pharmacology
Guinea Pigs
Heart / drug effects,  physiology*
Heart Ventricles
Least-Squares Analysis
Magnesium / pharmacology*
Manganese / pharmacology
Membrane Potentials / drug effects
Time Factors
Reg. No./Substance:
0/Calcium Channels; 67-42-5/Egtazic Acid; 7439-95-4/Magnesium; 7439-96-5/Manganese; 7440-39-3/Barium

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

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