mitoK_ATP channel activation in the postanoxic developing heart protects E-C coupling via NO-, ROS-, and PKC-dependent pathways

Abstract

Whereas previous studies have shown that opening of the mitochondrial ATP-sensitive K(+) (mitoK(ATP)) channel protects the adult heart against ischemia-reperfusion injury, it remains to be established whether this mechanism also operates in the developing heart. Isolated spontaneously beating hearts from 4-day-old chick embryos were subjected to 30 min of anoxia followed by 60 min of reoxygenation. The chrono-, dromo-, and inotropic disturbances, as well as alterations of the electromechanical delay (EMD), reflecting excitation-contraction (E-C) coupling, were investigated. Production of reactive oxygen species (ROS) in the ventricle was determined using the intracellular fluorescent probe 2',7'-dichlorofluorescin (DCFH). Effects of the specific mitoK(ATP) channel opener diazoxide (Diazo, 50 microM) or the blocker 5-hydroxydecanoate (5-HD, 500 microM), the nitric oxide synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME, 50 microM), the antioxidant N-(2-mercaptopropionyl)glycine (MPG, 1 mM), and the PKC inhibitor chelerythrine (Chel, 5 microM) on oxidative stress and postanoxic functional recovery were determined. Under normoxia, the baseline parameters were not altered by any of these pharmacological agents, alone or in combination. During the first 20 min of postanoxic reoxygenation, Diazo doubled the peak of ROS production and, interestingly, accelerated recovery of ventricular EMD and the PR interval. Diazo-induced ROS production was suppressed by 5-HD, MPG, or L-NAME, but not by Chel. Protection of ventricular EMD by Diazo was abolished by 5-HD, MPG, L-NAME, or Chel, whereas protection of the PR interval was abolished by L-NAME exclusively. Thus pharmacological opening of the mitoK(ATP) channel selectively improves postanoxic recovery of cell-to-cell communication and ventricular E-C coupling. Although the NO-, ROS-, and PKC-dependent pathways also seem to be involved in this cardioprotection, their interrelation in the developing heart can differ markedly from that in the adult myocardium.

Mitochondrial KATP channels in skeletal muscle: are protein kinases C and G, and nitric oxide synthase involved in the fatigue process?

“…29 Recently, we have reported no modification in the respiratory rate of mitochondria from chicken skeletal muscle as a result of treatment with 5-hydroxydecanoate in relation to different respiratory substrates. 32 In this regard, Sarre et al 33 suggested the existence of other factors involved in the ischemic process implied during fatigue, upstream activation of protein kinase C, and inhibiting diazoxide activation of mitoK ATP with chelerythrine. Costa et al 18 and Costa and Garlid 19 suggested that protein kinase G induces the opening of mitoK ATP in a way similar to that achieved by the channel activators, diazoxide and cromakalim, in heart, liver, and brain mitochondria.…”

“…In our case, we observed an increase in the presence of both drugs. It is possible that mitoK ATP could be activated by mitochondrial nitric oxide synthase, 33 a place the nitric oxide synthase inhibitor would not have access to.…”

Oxygen sensing and signal transduction in hypoxic pulmonary vasoconstriction

“…A small decrease in ATP may also open mitochondrial ATP-dependent potassium (mitoK ATP ) channels, which can increase ROS production under specific conditions [174]. In this regard, inhibitors of mitoK ATP completely inhibited HPV [175], although their specificity for mitoK ATP channels is under debate [176].…”

Impact of Hypoxia on Early Chick Embryo Growth and Cardiovascular Function

“…For example, the developing embryonic CV system can respond to acute changes in ventricular preload and afterload (10,11) as well as chronic changes in loading conditions (12,13). Acute hypoxia produces a dose-dependent depression in embryonic chick ventricular contractility (14) and the embryonic myocardium displays the ability to survive acute anoxia-reoxygenation with reduced apoptosis versus the mature heart (15,16). Chronic hypoxia late in gestation (d 19) is associated with cardiac contractile dysfunction, ventricular hypertrophy, and aortic intimal hypertrophy (3).…”