X

Forgot your Password

If you have forgotten your password, please enter your account email below and we will reset your password and email you the new password.

X

Login to SciCrunch

X

Register an Account

Delete Saved Search

Are you sure you want to delete this saved search?

NO

NIF LinkOut Portal

FILTERS

Electrophysiologic effects of acute myocardial ischemia: a theoretical study of altered cell excitability and action potential duration.

Authors:
Shaw RM, Rudy Y
Affiliation:
Journal:
Cardiovascular research

Abstract

OBJECTIVE: To study the ionic mechanisms of electrophysiologic changes in cell excitability and action potential duration during the acute phase of myocardial ischemia. METHODS: Using an ionic-based theoretical model of the cardiac ventricular cell, the dynamic LRd model, we have simulated the three major component conditions of acute ischemia (elevated [K]o, acidosis and anoxia) at the level of individual ionic currents and ionic concentrations. The conditions were applied individually and in combination to identify ionic mechanisms responsible for reduced excitability at rest potentials, delayed recovery of excitability, and shortened action potential duration. RESULTS: Increased extracellular potassium ([K]o) had the major effect on cell excitability by depolarizing resting membrane potential (Vrest), causing reduction in sodium channel availability. Acidosis caused a [K]o-independent reduction in maximum upstroke velocity, (dVm/dt)max. A transition from sodium-current dominated to calcium-current dominated upstroke occurred, and calcium current alone was able to sustain the upstroke, but only after sodium channels were almost completely (97%) inactivated. Acidic conditions prevented the transition to calcium dominated upstroke by acidic reduction of both sodium and calcium currents. Anoxia, simulated by lowering [ATP]i and activating the APT-dependent potassium current, IK(ATP), was the only process that could decrease action potential duration by more than 50% and reproduce AP shape changes that are observed experimentally. Acidic or anoxic depression of the L-type calcium current could not reproduce the observed action potential shape changes and APD shortening. Delayed recovery of excitability, known as 'post-repolarization refractoriness', was determined by the voltage-dependent kinetics of sodium channel recovery; Vrest depolarization caused by elevated [K]o increased the time constant of (dVm/dt)max recovery from tau = 10.3 ms at [K]o = 4.5 mM to tau = 81.4 ms at [K]o = 12 mM, reflecting major slowing of sodium-channel recovery. Anoxia and acidosis had little affect on tau. CONCLUSIONS: The major conditions of acute ischemia, namely elevated [K]o, acidosis and anoxia, applied at the ionic channel level are sufficient to simulate the major electrical changes associated with ischemia. Depression of membrane excitability and delayed recovery of excitability in the single, unloaded cell are caused by elevated [K]o with additional excitability depression by acidosis. Major changes in action potential duration and shape can only be accounted for by anoxia-dependent opening of IK(ATP).

  1. Welcome

    Welcome to NIF. Explore available research resources: data, tools and materials, from across the web

  2. Community Resources

    Search for resources specially selected for NIF community

  3. More Resources

    Search across hundreds of additional biomedical databases

  4. Literature

    Search Pub Med abstracts and full text from PubMed Central

  5. Insert your Query

    Enter your search terms here and hit return. Search results for the selected tab will be returned.

  6. Join the Community

    Click here to login or register and join this community.

  7. Categories

    Narrow your search by selecting a category. For additional help in searching, view our tutorials.

  8. Query Info

    Displays the total number of search results. Provides additional information on search terms, e.g., automated query expansions, and any included categories or facets. Expansions, filters and facets can be removed by clicking on the X. Clicking on the + restores them.

  9. Search Results

    Displays individual records and a brief description. Click on the icons below each record to explore additional display options.

X