Oxygen-Derived Free Radical Stress Activates Nonselective Cation Current in Guinea Pig Ventricular Myocytes: Role of Sulfhydryl Groups

• Published in: Circulation research Vol. 76; no. 5; pp. 812 - 824
• Main Authors: Jabr, Rita I, Cole, William C
• Format: Journal Article
• Language: English
• Published: Hagerstown, MD American Heart Association, Inc 01.05.1995; Lippincott; Lippincott Williams & Wilkins Ovid Technologies
• Subjects: Animals; Biological and medical sciences; Cells, Cultured; Free Radicals - metabolism; Free Radicals - pharmacology; Fundamental and applied biological sciences. Psychology; Guinea Pigs; Heart; Heart Ventricles - metabolism; Ion Transport - drug effects; Membrane Potentials; Oxidative Stress; Patch-Clamp Techniques; Sulfhydryl Compounds - metabolism; Vertebrates: cardiovascular system; Heart; Oxidative stress; Oxygen; Thiol; Rodentia; Ion transport; Electrophysiology; Heart ventricle; Ionic channel; Ionic current; Extracellular; Free radical; Myocyte; Vertebrata; Mammalia; Guinea pig; Membrane transport; Cations; Circulatory system
• ISSN: 0009-7330; 1524-4571
• DOI: 10.1161/01.RES.76.5.812

Oxygen-derived free radicals (O-Rs) cause alterations in cardiac electrical activity, including sustained depolarization, which may contribute to arrhythmic activity in reperfusion after ischemia. The ionic current(s) and cellular mechanism(s) underlying the sustained depolarization are not well defined. We used the whole-cell variant of the patch-clamp technique to study sustained depolarization in guinea pig ventricular myocytes during the extracellular application of O-Rs (generating systemdihydroxyfumaric acid, 3 to 6 mmol/L; FeCl3/ADP, 0.05:0.5 mmol/L). Myocytes superfused with O-Rs (pipette EGTA, 0.1 mmol/L) showed (1) sustained depolarization to between minus 40 and minus 10 mV, (2) oscillations in membrane potential, and (3) triggered activity. The depolarization resulted from an increase in quasi-steady state difference current reversing at approximate equal minus 18 mV, and the oscillations were due to transient inward current. The latter were inhibited with ryanodine (10 mu mol/L) or high pipette EGTA (5 mmol/L), but the steady state current was unaffected. Nonselective cation current (INSC) (recorded with Cs, Li, and Mg plus replacing K, Na, and Ca plus, respectively; 20 mmol/L tetraethylammonium chloride [TEA] and 5 mmol/L BAPTA in the pipette solution and 10 mmol/L TEA, 10 mu mol/L tetrodotoxin, and 10 mu mol/L nicardipine in the bath solution) was activated by O-Rs; the increase in current was unaffected by preventing changes in [Ca plus]i but was inhibited with dithiothreitol. Oxidizing agents (diamide and thimerosal) or caffeine (pipette EGTA, 0.1 mmol/L) produced a similar increase in membrane conductance. INSC activated with O-Rs, oxidizing agents, or caffeine was sensitive to SK&F 96365. O-R treatment was without effect when INSC was already activated with caffeine. The data suggest that (1) extracellular O-Rs activate a Ca plus-sensitive INSC in the absence of changes in [Ca sup 2 plus]i, (2) oxidative modification of extracellular sulfhydryl groups may be involved, and (3) this mechanism is different from the Ca plus-dependent activation of INSC by intracellular O-Rs, indicating that O-Rs may alter ion channel activity by differential mechanisms, depending on the compartment, extracellular or intracellular, in which they are present.(Circ Res. 1995;76:812-824.)