Cyclic GMP reduces ventricular myocyte stunning after simulated ischemia-reperfusion

Interaction between nitric oxide signaling and gap junctions during ischemic preconditioning: Importance of S-nitrosylation vs. protein kinase G activation

Much effort has been dedicated to exploring the mechanisms of IPC, and the GJ is one of the proposed targets of IPC. Several lines of evidence have indicated that NO affects GJ permeability regulation and expression of connexin isoforms. NO-induced stimulation of the sGC-cGMP pathway and the subsequent PKG activation could lead directly to connexin phosphorylation and GJ coupling modification. Additionally, because NO-induced cardioprotection against I/R injury beyond the cGMP/PKG-dependent pathway has been reported in isolated cardiomyocytes, it has been posited that NO-mediated GJ coupling might be independent from the activation of the NO-induced cGMP/PKG pathway during IPC. S-nitrosylation by NO exerts a major influence in IPC-induced cardioprotection. It has been suggested that NO-mediated cardioprotection during IPC was not dependent on sGC/cGMP/PKG but on SNO signaling. We need more researches to prove that which signaling pathway (S-nitrosylation or protein kinase G activation) is the major one modulating GJ coupling during IPC. The aim of review article is to discuss the possible signaling pathways of NO in regulating GJ during IPC.

Cyclic guanosine monophosphate signaling and phosphodiesterase-5 inhibitors in cardioprotection

Cyclic guanosine monophosphate (cGMP) is an important intracellular second messenger that mediates multiple tissue and cellular responses. The cGMP pathway is a key element in the pathophysiology of the heart and its modulation by drugs such as phosphodiesterase (PDE)-5 inhibitors and guanylate cyclase activators may represent a promising therapeutic approach for acute myocardial infarction, cardiac hypertrophy, heart failure, and doxorubicin cardiotoxicity in patients. In addition, PDE-5 inhibitors may prove to be innovative therapeutic agents for enhancing the chemosensitivity of doxorubicin while providing concurrent cardiac benefit.

Brain natriuretic peptide reverses the effects of myocardial stunning in rabbit myocardium

We tested the hypothesis that brain natriuretic peptide (BNP) would decrease the effects of myocardial stunning in rabbit hearts. We also examined the mechanisms responsible for these effects. In two groups of anesthetized open-chest rabbits, myocardial stunning was produced by 2 15-min occlusions of the left anterior descending artery separated by 15 min of reperfusion. The treatment group had BNP (10(-3) mol/l) topically applied to the stunned area. Hemodynamic and functional parameters were measured. Coronary flow and O2 extraction were used to determine myocardial O2 consumption. In separate animals, we measured the function of isolated control and simulated ischemia (95% N2/5% CO2, 15 min)-reperfusion ventricular myocytes with BNP or C-type natriuretic peptide (10(-8)-10(-7) mol/l) followed by KT5823 (10(-6) mol/l, cyclic GMP protein kinase inhibitor). In the in vivo control group, baseline delay to contraction was 47+/-4 ms and after stunning it increased to 71+/-10 ms. In the treatment group, baseline delay to contraction was 40+/-7 ms, and after stunning and BNP it did not significantly increase (43+/-6 ms). Neither stunning nor BNP administration affected regional O2 consumption. In control myocytes, BNP (10(-7) mol/l) decreased the percent shortening from 6.7+/-0.4 to 4.5+/-0.2%; after KT5823 administration, the percent shortening increased to 5.4+/-0.5%. In ischemia-reperfusion myocytes, BNP (10(-7) mol/l) decreased the percent shortening less from 5.0+/-0.5 to 3.8+/-0.2%; KT5823 administration did not increase the percent shortening (3.8+/-0.2%). BNP similarly and significantly increased cyclic GMP levels in control and stunned myocytes. The data illustrated that BNP administration reversed the effects of stunning and its mechanism may be independent of the cyclic GMP protein kinase.

Atrial natriuretic peptide reverses the negative functional effects of stunning in rabbit myocardium

We tested the hypothesis that atrial natriuretic peptide (ANP) would decrease both the effects of myocardial stunning and oxygen consumption in rabbit hearts. In two groups of anesthetized open-chest rabbits, myocardial stunning was produced by two 15 min occlusions of the left anterior descending (LAD) artery separated by 15 min of reperfusion. Either ANP (0.2 mg) or vehicle (lactated Ringers) was then injected into the affected area of the left ventricle. In a third group, ANP was injected into the LAD region of non-stunned rabbits. Hemodynamic (heart rate, aortic and left ventricular pressures) and functional (wall thickening (WT), delay of onset of WT, and rate of WT) parameters were measured. Coronary blood flow (microspheres) and O2 extraction (microspectrophotometry) were used to determine myocardial O2 consumption. Stunning was demonstrated by an increase in the time delay to contraction and depressed WT. In the control group, baseline delay to contraction was 25+/-7 ms, and this increased to 84+/-16 following stunning and vehicle administration. In the ANP group, baseline delay was 20+/-6 at baseline and after stunning and ANP administration it was 30+/-7. Wall thickening decreased by approximately 30% with stunning and vehicle but only 8% in the ANP treated hearts. Stunning did not affect regional O2 consumption (6.0+/-1.1 stunned vs. 7.4+/-1.2 mlO2/min/100g non-stunned). ANP administration did not affect O2 consumption (7.3+/-1.7 stunned vs. 6.4+/-1.0 non-stunned). We therefore concluded that ANP administration reversed the effects of stunning without alteration in local O2 consumption in stunned myocardium.

Effects of cyclic GMP and its protein kinase on the contraction of ventricular myocytes from hearts after cardiopulmonary arrest

Hearts undergoing cardiopulmonary arrest and resuscitation have depressed function and may have changes in signal transduction. We hypothesized that the cyclic GMP (cGMP) signaling pathway would be altered in the post-resuscitation heart. This was studied in ventricular myocytes from 7 anesthetized open-chest rabbits. Cardiopulmonary arrest was achieved for 10 min through ventricular fibrillation and respirator shutdown. After cardiopulmonary arrest, respiration was resumed, the heart was defibrillated, and the heart recovered for 15 min. Seven additional rabbits served as controls. Myocyte function was measured via a video edge detector. Myocytes were treated with 8-bromo-cGMP (10(-5)-10(-6) mol/L) followed by KT5823 (10(-6) mol/L, cGMP protein kinase inhibitor). The baseline percent shortening was significantly depressed in the cardiac arrest myocytes compared with control (3.3 +/- 0.1 vs. 5.5 +/- 0.3%). Treatment with 8-Br-cGMP similarly and dose-dependently reduced cell contraction in both cardiac arrest (-24%) and control (-25%) myocytes. The negative effect of 8-Br-cGMP was partially reversed by KT5823 in control myocytes, but not in the arrest group, indicating reduced involvement of cGMP protein kinase. Multiple proteins were specifically phosphorylated when cGMP was present, but the degree of phosphorylation was significantly less in myocytes after cardiac arrest. The data suggested that the basal contraction was reduced, but the functional response to 8-Br-cGMP was preserved in myocytes from cardiopulmonary arrested hearts. The results also indicated that the action of cGMP appeared to be mainly through non-cGMP protein kinase pathways in the post-resuscitation heart.

Cyclic GMP reduces myocardial stunning through non-cyclic GMP protein kinase mechanisms

We tested the hypothesis that myocardial stunning would be reduced by increased cyclic GMP and cGMP protein kinase activity. Hearts were instrumented in eight open-chest anesthetized dogs. The left anterior descending coronary artery (LAD) was occluded for 15 minutes followed by a 30-minute recovery and infusion of 8-Bromo-cGMP (0.1 and 1 microg/kg/min) during functional and metabolic data collection. Myocytes from circumflex and LAD regions were then used to obtain data at baseline, with 8-Br-cGMP (10(-7, -6, -5) M) and KT5823 10(-6) M, cGMP protein kinase inhibitor. The in vivo time delay of regional shortening increased significantly from 55 +/- 12 to 99 +/- 3 msec following stunning, but was reduced to 81 +/- 2 by 1 microg/kg/min 8-Br-cGMP. The % regional work during systole decreased during stunning (93 +/- 2 to 76 +/- 8%), but was restored by 8-Br-cGMP (91 +/- 7). Stunning lengthened the time of myocyte contraction and relaxation and reduced baseline shortening. 8-Br-cGMP reduced myocyte shortening in both regions. However, KT5823 only restored myocyte shortening in controls. These data indicated that regional myocardial stunning could be reduced by cyclic GMP but this appeared to be through non-cGMP protein kinase mechanisms.

Alterations in nitric oxide-cGMP pathway in ventricular myocytes from obese leptin-deficient mice

Leptin is a regulator of body weight and affects nitric oxide (NO) production. This study was designed to determine whether the myocardial NO-cGMP signal transduction system was altered in leptin-deficient obese mice. Contractile function, guanylyl cyclase activity, and cGMP-dependent protein phosphorylation were assessed in ventricular myocytes isolated from genetically obese (B6.V-Lepob) and age-matched lean (C57BL/6J) mice. There were no differences in baseline contraction between the lean and obese groups. After stimulation with the NO donor S-nitroso-N-acetyl-penicillamine (SNAP, 10-6 and 10-5 M) or a membrane-permeable cGMP analog 8-bromo-cGMP (8-Br-cGMP, 10(-6) and 10(-5) M), cell contractility was depressed. However, 8-Br-cGMP had significantly greater effects in obese mice than in lean controls with percent shortening reduced by 47 vs. 39% and maximal rate of shortening decreased by 46 vs. 36%. The negative effects of SNAP were similar between the two groups. Soluble guanylyl cyclase activity was not attenuated. This suggests that the activity of the cGMP-independent NO pathway may be enhanced in obesity. The phosphorylated protein profile of cGMP-dependent protein kinase showed that four proteins were more intensively phosphorylated in obese mice, which suggests an explanation for the enhanced effect of cGMP. These results indicate that the NO-cGMP signaling pathway was significantly altered in ventricular myocytes from the leptin-deficient obese mouse model.

The expression pattern of nitric oxide-sensitive guanylyl cyclase in the rat heart changes during postnatal development

Nitric oxide (NO)-releasing drugs such as glyceryl trinitrate have been used in the treatment of ischemic heart disease for more than a century. Nevertheless, a detailed analysis of the expression of the NO target enzyme soluble guanylyl cyclase (sGC) in the heart is missing. The aim of the current study was to elucidate the expression, cell distribution, and activity of sGC in the rat heart during postnatal development. Using a novel antibody raised against a C-terminal peptide of the rat beta(1)-subunit of sGC, the enzyme was demonstrated in early postnatal and adult hearts by Western blotting analyses, showing maximal expression in 10-day-old animals. Measurements of basal, NO-, and NO/YC-1-stimulated sGC activity revealed an increase of sGC activity in hearts from neonatal to 10-day-old rats, followed by a subsequent decrease in adult animals. As shown by immunohistochemical analysis, sGC expression was present in vascular endothelium and smooth muscle cells in neonatal heart but expression shifted to endothelial cells in adult animals. In isolated cardiomyocytes, sGC activity was not detectable under basal conditions but significant sGC activity could be detected in the presence of NO. An increase in expression during the perinatal period and changes in the cell types expressing sGC at different phases of development suggest dynamic regulation rather than constitutive expression of the NO receptor in the heart.

Nitric oxide and cGMP protein kinase activity in aged ventricular myocytes

We tested the hypothesis that nitric oxide-induced negative functional effects through cGMP would be reduced in aged cardiac myocytes. Maximum rate of shortening (R(max)) and percent shortening of ventricular myocytes from young (6 mo) and old (3 y) rabbits were studied using a video edge detector. cGMP-dependent phosphorylation was examined by electrophoresis and autoradiography. Myocytes received a nitric oxide donor S-nitroso-N-acetyl-penicillamine (SNAP, 10(-7), 10(-6), and 10(-5) M) followed by KT-5823 (10(-6) M), a cGMP protein kinase inhibitor. Baseline function was similar in young and old myocytes (89.1 +/- 4.5 young vs. 86.4 +/- 8.3 microm/s old R(max), 5.6 +/- 0.3 vs. 5.2 +/- 0.7%shortening). SNAP (10(-5) M) decreased R(max) in both young (25%, n = 6) and old myocytes (24%, n = 7). SNAP also reduced percent shortening by 28% in young and 23% in old myocytes. The negative effects of SNAP were partially reversed by KT-5823 only in young myocytes. Multiple proteins were phosphorylated by cGMP, and KT-5823 could reduce this effect. The degree of phosphorylation was significantly less in old myocytes. These results suggest that the functional response of ventricular myocytes to nitric oxide was preserved during aging. However, the importance of cGMP-dependent protein phosphorylation was decreased, indicating a shift to other pathways.

Interaction between cyclic GMP protein kinase and cyclic AMP may be diminished in stunned cardiac myocytes

We tested the hypothesis that the importance of the negative functional effects of the cyclic GMP protein kinase would be reduced in stunned (simulated ischemia/reperfusion) cardiac myocytes. Ventricular cardiac myocytes were isolated from New Zealand white rabbits (N=7). Myocytes were studied at baseline and after simulated ischemia (15 min of 95% N(2)-5% CO(2) at 37 degrees C) followed by simulated reperfusion (reoxygenation). Cell shortening was studied with a video edge detector; O(2) consumption was measured using O(2) electrodes. Protein phosphorylation was measured autoradiographically after gel electrophoresis. Functional and metabolic data were acquired after: (1) 8-(4-chlorophenylthio)guanosine-3',5'-monophosphate (PCPT, cGMP protein kinase agonist) 10(-7) or 10(-5) M; (2) 8-Br-cAMP 10(-5) M followed by PCPT 10(-7) or 10(-5) M; (3) beta-phenyl-1, N(2)-etheno-8-bromoguanosine-3',5'-monophosphorothioate, SP-isomer (SP, cGMP protein kinase agonist) 10(-7) or 10(-5) M; (2) 8-Br-cAMP 10(-5) M followed by SP 10(-7) or 10(-5) M. At baseline, percent of shortening (Pcs) and maximal rate of shortening (Rs) were significantly lower in the stunned myocytes (Pcs: 5.0+/-0.2% control vs. 3.8+/-0.3 stunned; Rs: 64.8+/-5.9 microm/s control vs. 46.9+/-4.8 stunned). In both groups, PCPT and SP dose-dependently decreased Pcs and Rs. The effects were slightly, but not significantly, less in stunned myocytes. 8-Br-cyclic AMP significantly increased function in control, but not stunned myocytes (Pcs, 4.5+/-0.5 to 6.2+/-0.8 control vs. 3.1+/-0.2 to 3.6+/-0.2 stunned). The negative functional effects of PCPT and SP were diminished after 8-Br-cyclic AMP in control (from -39% to-29%) and diminished significantly more in the stunned myocytes (-19%). PCPT and cyclic AMP phosphorylated similar protein bands. In stunned myocytes, three (22, 31 and 53 kDa) bands were enhanced less by PCPT.

Reduction in the level of cardiac cyclic GMP worsens contractile delay in myocardial stunning

We tested the hypothesis that a reduction in the level of myocardial cyclic GMP would worsen the contractile delay associated with myocardial stunning. Two groups of 12 anesthetized open-chest New Zealand white rabbits were utilized. Myocardial stunning was produced by two 15-min occlusions of the left anterior descending coronary artery followed by 15 min of reperfusion. Either control vehicle (saline + 1% DMSO) or 1H-[1,2,4]oxadiazolo[4, 3-a]quinoxalin-1-one (ODQ 10(-4) M, a guanylate cyclase inhibitor) was topically applied to the left ventricular surface of the rabbit hearts. Left ventricular and aortic pressures along with wall thickness parameters were determined. Coronary blood flow (microspheres) and O(2) extraction (microspectrophotometry) were used to determine myocardial O(2) consumption. Myocardial stunning was observed in the control group through an increased delay in onset of wall thickening (46.2 +/- 7.3 vs 76.6 +/- 17.5 ms). There was no significant effect of stunning on the rate of wall thickening (21.8 +/- 9.5 vs 18.1 +/- 3.4 mm/s) or O(2) consumption (stun 4.6 +/- 0.6, control 4.8 +/- 0.4 ml O(2)/min/100 g). After treatment with ODQ 10(-4) M, both delay (43.9 +/- 9.6 vs 134.1 +/- 30.0 ms) and myocardial O(2) consumption (stun 5.9 +/- 0.6, control 5.9 +/- 0. 7) increased significantly compared to control. There was no significant change in the rate of wall thickening. We conclude that decreasing cyclic GMP worsens stunning by increasing delay in onset of wall thickening and increasing local O(2) costs in the stunned region.