Experimental model of effects on normal tissue of injury current from ischemic region

An ischemic myocardial region contains cells with a depolarized resting membrane potential. This depolarization leads to an intercellular current flow between the ischemic region and the surrounding normal myocardial cells, which has been termed an "injury current." We have devised an experimental model system in which an isolated rabbit ventricular cell is electrically coupled to a model depolarized cell to evaluate the effects of this injury current on the electrical properties of a normal ventricular cell. We found that the action potential duration of the isolated cell could be reversibly altered by varying the coupling resistance such that the action potential duration was shortened by high values of coupling resistance but could be considerably prolonged by lower resistance coupling. We did not observe automaticity in the isolated cell as a consequence of coupling to the depolarized model. The changes in action potential duration were accompanied by alterations in the frequency at which the isolated cell could respond to repetitive stimuli. In addition, the depolarization of the isolated cell produced by the electrical coupling led to a significant increase in the cellular excitability. This last effect may be of particular importance in understanding the mechanisms for origination of arrhythmias in the border zone of myocardial ischemia.