ELECTROPHYSIOLOGICAL EFFECTS OF 4-HYDROXYNONENAL, AN ALDEHYDIC PRODUCT OF LIPID-PEROXIDATION, ON ISOLATED RAT VENTRICULAR MYOCYTES

Aldehydic products of lipid peroxidation, such as 4-hydroxynonenal (4- HNE), have been implicated in the etiology of pathological changes und er oxidative stress. To identify the mechanism by which 4-HNE alters c ellular excitability, its effects on isolated rat ventricular myocytes were studied. Superfusion with 100 to 880 mu mol/L 4-HNE led to a tim e- and concentration-dependent rigor shortening of myocytes. A reducti on in [Ca2+](o) and inhibition of transsarcolemmal Ca2+ transport by 1 mmol/L La3+ did not affect either the magnitude or the time course of 4-HNE-induced myocyte rigor. Superfusion of myocytes with 400 mu mol/ L 4-HNE led to an increase in the action potential duration, progressi ve depolarization of the resting membrane potential, and an increase i n the input resistance (R(in)) of the myocyte (phase I), followed by a loss of electrical excitability. Continued superfusion with 4-HNE re sulted in membrane hyperpolarization and a prominent decrease in the R (in) (phase II), The decrease in R(in) coincided with myocyte rigor. I n whole-cell voltage-clamp experiments, superfusion with 4-HNE inhibit ed current through the inward rectifier K+ channel (I-K1). 4-HNE had n o effect on either the magnitude or the rate of ''rundown'' of L-type Ca2+ currents. Exposure to 4-HNE led to an increase in the magnitude o f the fast inward Na+ current (I-Na). The voltage dependence of the st eady state parameters for activation and inactivation of I-Na shifted to more positive potentials, with a resultant increase in the window c urrent. 4-HNE-induced myocyte rigor was accompanied by a large increas e in time-independent currents that displayed linear dependence on the membrane potential and were inhibited by glibenclamide, suggesting ac tivation of the ATP-sensitive K+ channel. Steady state currents record ed in Cs+-containing Ringer's solution with La3+ 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 th e 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. The se observations indicate that 4-HNE-induced membrane depolarization ma y be due to an inhibition of I-K1. Changes in voltage dependence of I- Na, inhibition of I-K1 and membrane depolarization appear to contribut e to the prolongation of the action potential, observed during phase I . Depletion of [ATP], may be responsible for changes observed during p hase II, ie, activation of the ATP-sensitive K+ channels, membrane hyp erpolarization, decrease in R(in), and rigor shortening of the myocyte s. These results suggest that stable products of lipid peroxidation, s uch as 4-HNE, are proarrhythmic and may contribute to the cytotoxic ef fects of oxidative stress.