Comparison of the effects of regional ischemia and hyperkalemia on the membrane action potentials of the in situ pig heart. Experimental Cardiology Group, University of North Carolina at Chapel Hill.
BACKGROUND
This study was designed to determine the role of increased extracellular potassium [K+]e on action potential duration (APD) in the in situ porcine heart during acute regional no-flow ischemia.


RESULTS
In open chest, anesthetized swine, an arterial shunt from the carotid artery to the mid-left anterior descending coronary artery was created through which a solution of KCl was infused to raise [K+]e. Myocardial [K+]e was determined by potassium-sensitive electrodes, and transmembrane action potential was recorded by floating glass microelectrode. During the first 2 minutes of ischemia, APD at 90% repolarization (APD90) lengthened by 31.2 +/- 1.1 msec (P < 0.05). The comparable increase in [K+]e alone shortened APD90. During the next 6 minutes of ischemia, [K+]e rose to 11.3 +/- 0.3 mM and APD90 showed a decrease. However, the comparable increase in [K+]e by infusion of KCl caused further shortening of APD90 at similar levels of [K+]e.


CONCLUSIONS
Acutely ischemic myocardium showed a brief increase in APD90 during the first 2 minutes of ischemia, followed by a fall in APD90 after 2 minutes of ischemia, but the shortening is less than anticipated by the rise in [K+]e. Thus, we hypothesize that other component(s) of ischemia may inhibit action potential repolarization.
Watanabe
I
I
Kanda
A
A
Engle
C L
CL
Gettes
L S
LS
D000200:Action Potentials; D000818:Animals; D005260:Female; D006321:Heart / Q000503:physiopathology*; D006947:Hyperkalemia / Q000503:physiopathology*; D008297:Male; D017202:Myocardial Ischemia / Q000503:physiopathology*; D013552:Swine