Reactive oxygen species alters the electrophysiological properties and raises [Ca²⁺]iin intracardiac ganglion neurons

We have investigated the effects of the reactive oxygen species (ROS) donors hydrogen peroxide (H(2)O(2)) and tert-butyl hydroperoxide (t-BHP) on the intrinsic electrophysiological characteristics: ganglionic transmission and resting [Ca(2+)](i) in neonate and adult rat intracardiac ganglion (ICG) neurons. Intracellular recordings were made using sharp microelectrodes filled with either 0.5 M KCl or Oregon Green 488 BAPTA-1, allowing recording of electrical properties and measurement of [Ca(2+)](i). H(2)O(2) and t-BHP both hyperpolarized the resting membrane potential and reduced membrane resistance. In adult ICG neurons, the hyperpolarizing action of H(2)O(2) was reversed fully by Ba(2+) and partially by tetraethylammonium, muscarine, and linopirdine. H(2)O(2) and t-BHP reduced the action potential afterhyperpolarization (AHP) amplitude but had no impact on either overshoot or AHP duration. ROS donors evoked an increase in discharge adaptation to long depolarizing current pulses. H(2)O(2) blocked ganglionic transmission in most ICG neurons but did not alter nicotine-evoked depolarizations. By contrast, t-BHP had no significant action on ganglionic transmission. H(2)O(2) and t-BHP increased resting intracellular Ca(2+) levels to 1.6 ( +/- 0.6, n = 11, P < 0.01) and 1.6 ( +/- 0.3, n = 8, P < 0.001), respectively, of control value (1.0, approximately 60 nM). The ROS scavenger catalase prevented the actions of H(2)O(2), and this protection extended beyond the period of application. Superoxide dismutase partially shielded against the action of H(2)O(2), but this was limited to the period of application. These data demonstrate that ROS decreases the excitability and ganglionic transmission of ICG neurons, attenuating parasympathetic control of the heart.