Cellular electrophysiological basis for oxygen radical-induced arrhythmias. A patch-clamp study in guinea pig ventricular myocytes.
BACKGROUND
Oxygen radicals have been implicated in the pathogenesis of reperfusion arrhythmias. However, the basic electrophysiological alterations accompanying the effects of oxygen radicals on action potential (AP) are poorly understood.


RESULTS
We investigated the effects of oxygen radicals generated by dihydroxyfumarate (DHF, 5 mM) on AP parameters and on ionic currents in patch-clamped guinea pig ventricular myocytes. DHF consistently caused a marked prolongation of AP duration, which was already significant after 60 seconds of exposure and continued to increase over time. Within 5 minutes, the majority of cells developed early afterdepolarizations (EADs) or became unexcitable. Both AP prolongation and occurrence of EADs were completely prevented in the presence of the oxygen radical scavengers superoxide dismutase (SOD) and catalase (CAT). Prolongation of AP duration was accompanied by a marked decreased in time-dependent potassium current (IK) and calcium current (ICa). The inward rectifier K current (IK1) was unaffected, suggesting no widespread changes in membrane properties. IK and ICa alterations were also significantly reduced by SOD and CAT. In additional experiments, intracellular calcium levels were kept constantly low by addition of 200 microM ethyleneglycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetra-acetic acid (EGTA) to the pipette solution. Under these conditions, the effects of DHF on AP duration and the occurrence of EADs were largely prevented. However, EGTA did not prevent cells from becoming unexcitable, nor did it affect the decrease in both IK and ICa upon exposure to DHF.


CONCLUSIONS
Exposure to an exogenous source of oxygen radicals may induce major electrophysiological alterations in isolated myocytes, which might be related to changes in specific ionic currents and in level of intracellular calcium. These alterations occur with a time course consistent with the rapid onset of ventricular arrhythmias in reperfused hearts.
Cerbai
E
E
Institute of Pharmacology, University of Ferrara, Italy.
Ambrosio
G
G
Porciatti
F
F
Chiariello
M
M
Giotti
A
A
Mugelli
A
A
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000209:etiology*; D016166:Free Radical Scavengers; D005609:Free Radicals / Q000009:adverse effects; D005650:Fumarates / Q000494:pharmacology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D016623:Ion Pumps / Q000187:drug effects; D015428:Myocardial Reperfusion Injury / Q000209:etiology*; D009206:Myocardium / Q000473:pathology; D010100:Oxygen / Q000009:adverse effects*; D013997:Time Factors
D016166:Free Radical Scavengers; D005609:Free Radicals; D005650:Fumarates; D016623:Ion Pumps; C005998:dihydroxyfumarate; D010100:Oxygen