Electrophysiological Effects of 4-Hydroxynonenal, an Aldehydic Product of Lipid Peroxidation, on Isolated Rat Ventricular Myocytes

Abstract

Abstract Aldehydic products of lipid peroxidation, such as 4-hydroxynonenal (4-HNE), have been implicated in the etiology of pathological changes under oxidative stress. To identify the mechanism by which 4-HNE alters cellular excitability, its effects on isolated rat ventricular myocytes were studied. Superfusion with 100 to 880 μmol/L 4-HNE led to a time- and concentration-dependent rigor shortening of myocytes. A reduction in [Ca 2+ ] o and inhibition of transsarcolemmal Ca 2+ transport by 1 mmol/L La 3+ did not affect either the magnitude or the time course of 4-HNE–induced myocyte rigor. Superfusion of myocytes with 400 μmol/L 4-HNE led to an increase in the action potential duration, progressive depolarization of the resting membrane potential, and an increase in the input resistance (R in ) of the myocyte (phase I), followed by a loss of electrical excitability. Continued superfusion with 4-HNE resulted in membrane hyperpolarization and a prominent decrease in the R in (phase II). The decrease in R in coincided with myocyte rigor. In whole-cell voltage-clamp experiments, superfusion with 4-HNE inhibited current through the inward rectifier K + channel (I K1 ). 4-HNE had no effect on either the magnitude or the rate of “rundown” of L-type Ca 2+ currents. Exposure to 4-HNE led to an increase in the magnitude of the fast inward Na + current (I Na ). The voltage dependence of the steady state parameters for activation and inactivation of I Na shifted to more positive potentials, with a resultant increase in the window current. 4-HNE–induced myocyte rigor was accompanied by a large increase in time-independent currents that displayed linear dependence on the membrane potential and were inhibited by glibenclamide, suggesting activation of the ATP-sensitive K + channel. Steady state currents recorded in Cs + -containing Ringer’s solution with La 3+ and tetrodotoxin and Cs + -containing internal solution (leak currents) were not affected by 4-HNE. Superfusion with 4-HNE resulted in a significant decrease in the cellular concentration of nonprotein thiols and a severe decrease in [ATP] i . The energy charge of the myocytes fell from 0.9 to 0.3. These observations indicate that 4-HNE–induced membrane depolarization may be due to an inhibition of I K1 . Changes in voltage dependence of I Na , inhibition of I K1 , and membrane depolarization appear to contribute to the prolongation of the action potential, observed during phase I. Depletion of [ATP] i may be responsible for changes observed during phase II, ie, activation of the ATP-sensitive K + channels, membrane hyperpolarization, decrease in R in , and rigor shortening of the myocytes. These results suggest that stable products of lipid peroxidation, such as 4-HNE, are proarrhythmic and may contribute to the cytotoxic effects of oxidative stress.