This study was conducted to examine the role of myocardial ATP-sensitive potassium (K ATP ) channels in exercise-induced protection from ischaemia-reperfusion (I-R) injury. Female rats were either sedentary (Sed) or exercised for 12 weeks (Tr). Hearts were excised and underwent a 1-2 h regional I-R protocol. Prior to ischaemia, hearts were subjected to pharmacological blockade of the sarcolemmal K ATP channel with HMR 1098 (SedHMR and TrHMR), mitochondrial blockade with 5-hydroxydecanoic acid (5HD; Sed5HD and Tr5HD), or perfused with buffer containing no drug (Sed and Tr). Infarct size was significantly smaller in hearts from Tr animals (35.4 ± 2.3 versus 44.7 ± 3.0% of the zone at risk for Tr and Sed, respectively). Mitochondrial K ATP blockade did not abolish the training-induced infarct size reduction (30.0 ± 3.4 versus 38.0 ± 2.6 in Tr5HD and Sed5HD, respectively); however, sarcolemmal K ATP blockade completely eradicated the training-induced cardioprotection. Infarct size was 71.2 ± 3.3 and 64.0 ± 2.4% of the zone at risk for TrHMR and Sed HMR. The role of sarcolemmal K ATP channels in Tr-induced protection was also supported by significant increases in both subunits of the sarcolemmal K ATP channel following training. LV developed pressure was better preserved in hearts from Tr animals, and was not influenced by addition of HMR 1098. 5HD decreased pressure development regardless of training status, from 15 min of ischaemia through the duration of the protocol. This mechanical dysfunction was likely to be due to a 5HD-induced increase in myocardial Ca 2+ content following I-R. The major findings of the present study are: (1) unlike all other known forms of delayed cardioprotection, infarct sparing following chronic exercise was not abolished by 5HD; (2) pharmacological blockade of the sarcolemmal K ATP channel nullified the cardioprotective benefits of exercise training; and (3) increased expression of sarcolemmal K ATP channels was observed following chronic training.

The cardioprotective effects of short-term exercise against myocardial ischaemia-reperfusion injury in male and female rats were examined. We subjected male and female rats to 0 (Sed; n = 8 males and 8 females), 1 (1 day; n = 10 males and 8 females), or 5 (5 day; n = 6 males and 6 females) days of treadmill running. Langendorff-perfused hearts underwent 1 h of regional ischaemia and 2 h of reperfusion, and infarct size (expressed as a percentage of the zone at risk; ZAR), left ventricular pressure development, and coronary flow were measured for each heart. Preischaemic pressure development and coronary flow did not differ between the sexes nor were they influenced by exercise. Sed females had significantly smaller infarct sizes (25 ± 3%) than Sed male hearts (37 ± 3%; P < 0.001). Short-term running significantly reduced infarct size following 1 day (27 ± 3%; P < 0.05) and 5 days (30 ± 4%; P < 0.10) of exercise in males. One day of running did not reduce infarct size in females (19 ± 3%; P = NS), but 5 day females did show a significant reduction in infarct size (13 ± 2%; P < 0.05). There was no relationship between postischaemic coronary vascular hyperaemia and infarct size across sexes or exercise training groups. Hearts from Sed females exhibited significantly higher manganese superoxide dismutase (MnSOD) protein expression than hearts from Sed males, but short-term exercise (neither 1 nor 5 days) did not alter MnSOD protein in either sex. Increased sarcolemmal ATP-sensitive K + (K ATP ) channel subunit protein expression (SUR2A and/or K ir 6.2) correlated closely with sex-dependent and exercise-acquired protection against myocardial infarction. These data indicate that: (1) sex-dependent and exercise-induced differences in the susceptibility of the heart to ischaemia-reperfusion injury are not associated with improved coronary flow or postischaemic hyperaemia; (2) increased MnSOD protein expression is not necessary for exercise-induced protection from infarction; and (3) one possible mechanism for sex-dependent and exercise-mediated reductions in infarct size involves an increased protein expression of cardiac sarcolemmal K ATP channels.

Sex differences in myocardial infarct size are abolished by sarcolemmal KATP channel blockade in rat. Am J Physiol Heart Circ Physiol 290: H2644 -H2647, 2006. First published February 10, 2006 doi:10.1152/ajpheart.01291.2005.-This study was conducted to examine the relationship between myocardial ATP-sensitive potassium (KATP) channels and sex differences in myocardial infarct size after in vitro ischemia-reperfusion (I/R). Hearts from adult male and female Sprague-Dawley rats were excised and exposed to an I/R protocol (1 h of ischemia, followed by 2 h of reperfusion) on a modified Langendorff apparatus. Hearts from female rats showed significantly smaller infarct sizes than hearts from males (23 Ϯ 4 vs. 40 Ϯ 5% of the zone at risk, respectively; P Ͻ 0.05). Administration of HMR-1098, a sarcolemmal K ATP channel blocker, abolished the sex difference in infarct size (42 Ϯ 4 vs. 45 Ϯ 5% of the zone at risk in hearts from female and male rats, respectively; P ϭ not significant). Further experiments showed that blocking the KATP channels in ischemia, and not reperfusion, was sufficient to increase infarct size in female rats. These data demonstrate that sarcolemmal KATP channels are centrally involved in mechanisms that underlie sex differences in the susceptibility of the intact heart to I/R injury. heart; ischemia; reperfusion ISCHEMIC HEART DISEASE is the leading cause of death in both males and females in the industrialized world, with myocardial infarction being the most common manifestation of ischemic heart disease (18). Among humans, premenopausal women have a lower risk of cardiovascular disease than age-matched men, and there is growing evidence that there is a sex-specific difference in the susceptibility of the myocardium to infarction after ischemia in dogs (15), rats (1, 4), mice (10, 11), as well as in humans (19).The cellular basis for sex differences in the susceptibility of the heart to ischemia-reperfusion (I/R) injury has not been elucidated. However, there has been speculation that that sarcolemmal ATP-sensitive potassium (sarcK ATP ) channels are involved. This speculation derives from observations that, relative to males, the protein expression of sarcK ATP channel subunits [inwardly rectifying K ϩ (Kir)6.2 and sulfonylurea receptor (SUR)2a] is greater in hearts from females (4, 26). Additionally, treatment of heart-derived H9c2 cells with 17␤-estradiol elicits a marked increase in the expression of both Kir6.2 and SUR2a subunits and an increase in the resistance of those cells to hypoxia-induced Ca 2ϩ overload that, in turn, could be abolished by sarcK ATP channel blockade with HMR-1098 (25). Whereas these observations clearly implicate a role for sarcK ATP channels in the sex-dependent differences in the susceptibility of the heart to I/R injury, pharmacological blockade of sarcK ATP channels in the intact heart has not been performed to confirm their role in sex-dependent cardioprotection. Thus the major objective of this study was to determine whether blocking sarcK ATP channels would ab...

The use of short-term (1-5 days) treadmill running is becoming increasingly common as a model to study physiological adaptations following the exercise. Although the beneficial effects of acute exercise seem clear, a paucity of data exist describing potential markers of stress in response to forced running. We subjected male and female Sprague-Dawley rats to 0, 1, 2, 5, or 10 days of treadmill running. Twenty-four to 32 h after the last bout of exercise animals were killed and examined for training-induced changes in several physiological variables. No effect of skeletal citrate synthase activity was observed in the male animals after any duration, and only at 10 days of running did females show a significant increase in citrate synthase. Myocardial heat shock protein 72 (HSP72) content was higher in male rats than female rats, and exercise led to increased HSP72 in both sexes, although the time course was different between males and females. Animals displayed several markers of systemic stress in response to the treadmill running, and this was done in a sex-dependent manner. Serum corticosterone was significantly elevated in both sexes 24 h after exercise in three of four exercise groups. Corticosterone-binding globulin was higher in females, and decreased after running in female rats. Body and spleen weights decreased in males (but not females) in response to the exercise training, and running did not alter adrenal gland weights in either sex. These data indicate that in response to short-term treadmill running both male and female rats show signs of systemic stress, but that the pattern of changes occurs in a sex-specific manner.

A high peak brilliance, laser-based Compton-scattering-ray source, capable of producing quasimonoenergetic photons with energies ranging from 0.1 to 0.9 MeV has been recently developed and used to perform nuclear resonance fluorescence (NRF) experiments. Techniques for characterization of-ray beam parameters are presented. The key source parameters are the size (0:01 mm 2), horizontal and vertical divergence (6 Â 10 mrad 2), duration (16 ps), and spectrum and intensity (10 5 photons=shot). These parameters are summarized by the peak brilliance, 1:5 Â 10 15 photons=mm 2 =mrad 2 =s=0:1% bandwidth, measured at 478 keV. Additional measurements of the flux as a function of the timing difference between the drive laser pulse and the relativistic photoelectron bunch,-ray beam profile, and background evaluations are presented. These results are systematically compared to theoretical models and computer simulations. NRF measurements performed on 7 Li in LiH demonstrate the potential of Compton-scattering photon sources to accurately detect isotopes in situ.

No abstract

Suppressor of cytokine signalling-3 (SOCS-3) has been implicated in the onset of insulin resistance in non-muscle tissue. Thus, we examined the effects of exercise training on SOCS-3 expression and the potential role of SOCS-3 in muscle. Female Sprague-Dawley rats (5-8 months) were treadmill trained for 12 weeks and the muscles were removed 24 h after the last bout of exercise. Exercise training increased SOCS-3 mRNA expression by 80% and 154% in the plantaris and soleus muscle, respectively. To mimic the effects of increased SOCS-3 expression, SOCS-3 cDNA was cotransfected with a NF-kappa B (NF-κB) luciferase construct into cultured C2C12 myotubes. SOCS-3 overexpression increased NF-κB transcriptional activity by 27-fold. The proximal region of the IL-6 gene promoter contains a NF-κB consensus site, which contributes to increased IL-6 expression in various tissues. SOCS-3 cDNA was cotransfected into cultured C2C12 myotubes with either the IL-6 luciferase construct or a mutated NF-κB IL-6 luciferase construct. SOCS-3 overexpression increased IL-6 transcriptional activity by 15-fold, however, when the NF-κB site was mutated SOCS-3 failed to increase IL-6 transcriptional activity. We subsequently found that IL-6 mRNA expression was elevated in the plantaris and soleus muscles of the trained animals compared to the sedentary animals. Finally, exercise induced a significant reduction in IκBα and increased phosphorylation of Iκκ suggesting that NF-κB activation was elevated after exercise training. These data suggest that training-induced elevations in SOCS-3 expression in skeletal muscle may contribute to the exercise-induced increase in IL-6 expression through alterations in the mechanisms that mediate NF-κB activity.

Chicco AJ, Johnson MS, Armstrong CJ, Lynch JM, Gardner RT, Fasen GS, Gillenwater CP, Moore RL. Sex-specific and exercise-acquired cardioprotection is abolished by sarcolemmal KATP channel blockade in the rat heart. Am J Physiol Heart Circ Physiol 292: H2432-H2437, 2007. First published January 19, 2007; doi:10.1152/ajpheart.01301.2006.-The present study was conducted to determine whether the infarct sparing effect of shortterm exercise is dependent on the operation of the myocardial sarcolemmal ATP-sensitive K ϩ (KATP) channel. Adult male and female Sprague-Dawley rats were exercised on a motorized treadmill for 5 days. Twenty-four hours following the training or sedentary period, hearts were isolated and exposed to 1 h of regional ischemia followed by 2 h of reperfusion on a modified Langendorf apparatus in the presence or absence of the sarcolemmal KATP channel antagonist HMR-1098 (30 M). Following the ischemia-reperfusion protocol, infarct size was determined as a percentage of the total ischemic zone at risk (ZAR). Short-term exercise reduced infarct size by 24% in males (32 Ϯ 2% of ZAR; P Ͻ 0.01) and by 18% in females (26 Ϯ 2% of ZAR; P Ͻ 0.05). Sarcolemmal KATP channel blockade abolished the training-induced cardioprotection in both males and females, increasing infarct size to 43 Ϯ 3% and 52 Ϯ 4% of ZAR, respectively. In the absence of HMR-1098, infarct size was significantly lower in sedentary females than in males (33 Ϯ 4% vs. 42 Ϯ 2% of ZAR, respectively; P Ͻ 0.01). However, the presence of HMR-1098 abolished this sex difference, increasing infarct size by 58% in the sedentary females (P Ͻ 0.01) but having no effect on infarct size in sedentary males. This study demonstrates that the sex-specific and exercise-acquired resistance to myocardial ischemia-reperfusion injury is dependent on sarcolemmal KATP activity during ischemia. ischemia; infarction; sex differences; gender ISCHEMIC HEART DISEASE is a leading cause of mortality in industrialized countries throughout the world. Myocardial infarction is often the initial manifestation of ischemic heart disease, and survival is inversely proportional to the size of the myocardial infarction sustained (13). A variety of preconditioning stimuli has proven to be effective at reducing myocardial infarct size when administered immediately before ischemia (e.g, ischemic preconditioning and adenosine receptor agonists), but the protective effect of these treatments is lost after repetitive administration (38, 53). Exercise training, however, has been consistently shown to confer sustainable protection against myocardial infarction in animal models (10,26,40,56,57) and has been associated with improved survival following an ischemic event in humans (27,43). Despite substantial efforts to characterize the cardioprotective phenotype evoked by exercise training over the past decade, the precise mechanisms by which exercise reduces infarct size have not been fully elucidated.The infarct-sparing effect of exercise has been reported following both long-term (Ͼ10 wk) (9...