Mechanism of Preconditioning by Isoflurane in Rabbits: A Direct Role for Reactive Oxygen Species

LARGE quantities of reactive oxygen species (ROS) released during reperfusion after coronary artery occlusion damage proteins responsible for intracellular homeostasis, produce tissue injury, depress contractile function, and increase myocardial infarct size. In contrast, small quantities of ROS may exert beneficial effects during ischemia and reperfusion when released before a prolonged ischemic event. ROS derived from mitochondria during a brief ischemic episode produce preconditioning. Free radical scavengers administered during ischemic preconditioning (IPC) markedly attenuate the protective effect of the preconditioning stimulus on infarct size. These data suggest that IPC is mediated in part by small quantities of ROS released during preconditioning. Volatile anesthetics protect myocardium against infarction through a signal transduction pathway that includes adenosine type 1 receptors, protein kinase C, inhibitory guanine regulatory proteins, and mitochondrial and sarcolemmal adenosine triphosphate-regulated potassium (KATP) channels. A recent investigation by Müllenheim et al . provides compelling evidence that ROS also mediate myocardial protection produced by volatile anesthetics. We sought to confirm and extend these important results by examining the hypothesis that ROS scavengers inhibit isoflurane-induced protection against irreversible ischemic injury. We further tested the hypothesis that isoflurane directly generates ROS in rabbit ventricular myocardium in vivo using a confocal microscopic technique combined with the superoxide anion-specific fluorescent probe dihydroethidium

Reactive Oxygen Species Modulate Coronary Wall Shear Stress and Endothelial Function During Hyperglycemia

Hyperglycemia is associated with generation of reactive oxygen species (ROS), and this action may contribute to accelerated atherogenesis. We tested the hypothesis that hyperglycemia produces alterations in left anterior descending coronary artery (LAD) wall shear stress concomitant with endothelial dysfunction and ROS production in dogs (n = 12) instrumented for measurement of LAD blood flow, velocity, and diameter. Dogs were randomly assigned to receive vehicle (0.9% saline) or the superoxide dismutase mimetic 4- hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (tempol) and were administered intravenous infusions of d-glucose to achieve target blood glucose concentrations of 350 and 600 mg/dl (moderate and severe hyperglycemia, respectively). Endothelial function and ROS generation were assessed by coronary blood flow responses to acetylcholine (10, 30, and 100 ng/kg) and dihydroethidium fluorescence of myocardial biopsies, respectively. Indexes of wall shear stress were calculated with conventional fluid dynamics theory. Hyperglycemia produced dose-related endothelial dysfunction, increases in ROS production, and reductions in oscillatory shear stress that were normalized by tempol. The results suggest a direct association between hyperglycemia-induced ROS production, endothelial dysfunction, and decreases in oscillatory shear stress in vivo

Detection of TRPV4 channel current-like activity in Fawn Hooded hypertensive (FHH) rat cerebral arterial muscle cells.

The transient receptor potential vallinoid type 4 (TRPV4) is a calcium entry channel known to modulate vascular function by mediating endothelium-dependent vasodilation. The present study investigated if isolated cerebral arterial myocytes of the Fawn Hooded hypertensive (FHH) rat, known to display exaggerated KCa channel current activity and impaired myogenic tone, express TRPV4 channels at the transcript and protein level and exhibit TRPV4-like single-channel cationic current activity. Reverse transcription polymerase chain reaction (RT-PCR), Western blot, and immunostaining analysis detected the expression of mRNA transcript and translated protein of TRPV4 channel in FHH rat cerebral arterial myocytes. Patch clamp recording of single-channel current activity identified the presence of a single-channel cationic current with unitary conductance of ~85 pS and ~96 pS at hyperpolarizing and depolarizing potentials, respectively, that was inhibited by the TRPV4 channel antagonist RN 1734 or HC 067074 and activated by the potent TRPV4 channel agonist GSK1016790A. Application of negative pressure via the interior of the patch pipette increased the NPo of the TRPV4-like single-channel cationic current recorded in cell-attached patches at a patch potential of 60 mV that was inhibited by prior application of the TRPV4 channel antagonist RN 1734 or HC 067047. Treatment with the TRPV4 channel agonist GSK1016790A caused concentration-dependent increase in the NPo of KCa single-channel current recorded in cell-attached patches of cerebral arterial myocytes at a patch potential of 40 mV, which was not influenced by pretreatment with the voltage-gated L-type Ca2+ channel blocker nifedipine or the T-type Ca2+ channel blocker Ni2+. These findings demonstrate that FHH rat cerebral arterial myocytes express mRNA transcript and translated protein for TRPV4 channel and display TRPV4-like single-channel cationic current activity that was stretch-sensitive and activation of which increased the open state probability of KCa single-channel current in these arterial myocytes

PPARγ-Independent Side Effects of Thiazolidinediones on Mitochondrial Redox State in Rat Isolated Hearts

The effect of anti-diabetic thiazolidinediones (TZDs) on contributing to heart failure and cardiac ischemia/reperfusion (IR) injury is controversial. In this study we investigated the effect of select TZDs on myocardial and mitochondrial function in Brown Norway rat isolated hearts. In a first set of experiments, the TZD rosiglitazone was given acutely before global myocardial IR, and pre- and post-IR function and infarct size were assessed. In a second set of experiments, different concentrations of rosiglitazone and pioglitazone were administered in the presence or absence of the specific PPARγ antagonist GW9662, and their effects on the mitochondrial redox state were measured by online NADH and FAD autofluorescence. The administration of rosiglitazone did not significantly affect myocardial function except for transiently increasing coronary flow, but it increased IR injury compared to the control hearts. Both TZDs resulted in dose-dependent, reversible increases in mitochondrial oxidation which was not attenuated by GW9662. Taken together, these data suggest that TZDs cause excessive mitochondrial uncoupling by a PPARγ-independent mechanism. Acute rosiglitazone administration before IR was associated with enhanced cardiac injury. If translated clinically, susceptible patients on PPARγ agonists may experience enhanced myocardial IR injury by mitochondrial dysfunction