Sulfhydryl modification inhibits K+ (M) current with kinetics close to acetylcholine in rodent NG108-15 cells

Diazoxide-induced cardioprotection requires signaling through a redox-sensitive mechanism

Diazoxide, a selective opener of the mitochondrial ATP-sensitive potassium channel, has been shown to elicit tolerance to ischemia in cardiac myocytes and in perfused heart. However, the mechanism of this cardioprotection is poorly understood. Because reactive oxygen species (ROS) are recognized as important intracellular signaling molecules and have been implicated in ischemic preconditioning, we examined diazoxide-induced ROS production in adult cardiomyocytes. Cells treated with 50 micromol/L diazoxide showed a 173% increase in ROS production relative to baseline. 5-Hydroxydecanoate was found to attenuate the diazoxide-induced increase in ROS generation. The diazoxide-induced increase in ROS also was abrogated by the addition of either the antioxidant N-acetylcysteine (NAC) or N-mercaptopropionylglycine. We also examined the ability of NAC to block the protective effects of diazoxide in the perfused rat heart. After 20 minutes of global ischemia and 20 minutes of reflow, hearts perfused with 100 micromol/L diazoxide before ischemia showed significantly improved postischemic contractile function relative to untreated hearts (84% versus 29% of initial left ventricular developed pressure, respectively). Hearts treated with diazoxide in the presence of 4 mmol/L NAC recovered 53% of initial left ventricular developed pressure, whereas hearts treated with NAC alone recovered 46% of preischemic function. Using (31)P NMR spectroscopy, we found that, similar to preconditioning, diazoxide significantly attenuated ischemia-induced intracellular acidification and enhanced post- ischemic recovery of phosphocreatine levels, both of which were blocked by cotreatment with NAC. These data suggest that the cardioprotective actions of diazoxide are mediated by generation of a pro-oxidant environment.

Modulation and genetic identification of the M channel

Potassium channels constitute a superfamily of the most diversified ion channels, acting in delicate and accurate ways to control or modify many physiological and pathological functions including membrane excitability, transmitter release, cell proliferation and cell degeneration. The M-type channel is a unique ligand-regulated and voltage-gated K(+) channel showing distinct physiological and pharmacological characteristics. This review will cover some important progress in the study of M channel modulation, particularly focusing on membrane transduction mechanisms. The K(+) channel genes corresponding to the M channel have been identified and will be reviewed in detail. It has been a long journey since the discovery of M current in 1980 to our present understanding of the mysterious mechanisms for M channel modulation; a journey which exemplifies tremendous achievements in ion channel research and exciting discoveries of elaborate modulatory systems linked to these channels. While substantial evidence has accumulated, challenging questions remain to be answered.