Triphosphate-sensitive Potassium Channel Opener Research Articles

Pretreatment With Diazoxide Attenuates Spinal Cord Ischemia-Reperfusion Injury Through Signaling Transducer and Activator of Transcription 3 Pathway

Delayed paraplegia remains a feared complication of thoracoabdominal aortic intervention. Pharmacologic preconditioning with diazoxide (DZ), an adenosine 5'-triphosphate-sensitive potassium channel opener, results in neuroprotection against ischemic insult. However, the effects of DZ in spinal cord ischemia-reperfusion injury have not been fully elucidated. We hypothesized that DZ attenuates spinal cord ischemia-reperfusion injury through the signaling transducer and activator of transcription (STAT) 3 pathway. Adult male C57/BL6 mice received DZ (20 mg/kg) by oral gavage. Spinal cords were harvested at 0, 12, 24, 36, 48, and 60 hours after administration of DZ. The expression of phosphorylated STAT3 was assessed by Western blot analysis. Five groups were studied: DZ (DZ pretreatment, n= 8), ischemic control (phosphate-buffered saline pretreatment, n= 11), DZ+ STAT3 inhibitor LY5 (DZ pretreatment+ LY5, n= 8), LY5 (phosphate-buffered saline pretreatment+ LY5, n= 8), and sham (without cross-clamping, n= 5). Spinal cord ischemia was induced by 4 minutes of thoracic aortic cross-clamp. Functional scoring (Basso Mouse Score) was done at 12-hour intervals until 48 hours, and spinal cords were harvested for the evaluation of B-cell lymphoma 2 expression and histologic changes. The expression of phosphorylated STAT3 was significantly upregulated 36 hours after the administration of DZ. The motor function in the DZ group was significantly preserved compared with all other groups. The expression of B-cell lymphoma 2 in the DZ group was significantly higher than in the ischemic control, DZ+ LY5, and LY5 groups 48 hours after reperfusion. DZ preserves motor function in spinal cord ischemia-reperfusion injury by the STAT3 pathway. DZ may be beneficial clinically for use in spinal protection in aortic intervention.

Pinacidil stimulates osteoblast function in osteoblastic MC3T3-E1 cells

This study examined the effect of pinacidil, a nonselective adenosine triphosphate–sensitive potassium channel opener, on the function of osteoblastic MC3T3-E1 cells. Pinacidil caused a significant elevation of collagen synthesis, alkaline phosphatase activity, osteocalcin synthesis and mineralization in the cells (p < 0.05). Pinacidil significantly decreased the production of osteoclast differentiation inducing factors such as TNF-α, IL-6 and receptor activator of nuclear factor-κB ligand in the presence of antimycin A, which inhibits mitochondrial electron transport. Moreover, pinacidil prevented antimycin A-induced reactive oxygen species and nitrotyrosine production. These results demonstrate that pinacidil may have positive effects on skeletal structure.

Marked Hyperglycemia Attenuates Anesthetic Preconditioning in Human-induced Pluripotent Stem Cell-derived Cardiomyocytes

Anesthetic preconditioning protects cardiomyocytes from oxidative stress-induced injury, but it is ineffective in patients with diabetes mellitus. To address the role of hyperglycemia in the inability of diabetic individuals to be preconditioned, we used human cardiomyocytes differentiated from induced pluripotent stem cells generated from patients with or without type 2 diabetes mellitus (DM-iPSC- and N-iPSC-CMs, respectively) to investigate the efficacy of preconditioning in varying glucose conditions (5, 11, and 25 mM). Induced pluripotent stem cells were induced to generate cardiomyocytes by directed differentiation. For subsequent studies, cardiomyocytes were identified by genetic labeling with enhanced green fluorescent protein driven by a cardiac-specific promoter. Cell viability was analyzed by lactate dehydrogenase assay. Confocal microscopy was utilized to measure opening of the mitochondrial permeability transition pore and the mitochondrial adenosine 5'-triphosphate-sensitive potassium channels. Isoflurane (0.5 mM) preconditioning protected N-iPSC- and DM-iPSC-CMs from oxidative stress-induced lactate dehydrogenase release and mitochondrial permeability transition pore opening in 5 mM and 11 mM glucose. Isoflurane triggered mitochondrial adenosine-5'-triphosphate-sensitive potassium channel opening in N-iPSC-CMs in 5 mM and 11 mM glucose and in DM-iPSC-CMs in 5 mM glucose; 25 mM glucose disrupted anesthetic preconditioning-mediated protection in DM-iPSC- and N-iPSC-CMs. The opening of mitochondrial adenosine 5'-triphosphate-sensitive potassium channels are disrupted in DM-iPSC-CMs in 11 mM and 25 mM glucose and in N-iPSC-CMs in 25 mM glucose. Cardiomyocytes derived from healthy donors and patients with a specific disease, such as diabetes in this study, open possibilities in studying genotype- and phenotype-related pathologies in a human-relevant model.

Effects of Cyclooxygenase-2 Inhibitor and Adenosine Triphosphate–Sensitive Potassium Channel Opener in Syngeneic Mouse Islet Transplantation

In the initial days after transplantation, islet grafts may be attacked by cytokines via cyclooxygenase-2 (COX-2), producing primary nonfunction. In addition, chronic overstimulation of β-cells may impair insulin secretion. To enhance the function of transplanted islets, the present study investigated the effects of rofecoxib, a COX-2 inhibitor, and NN414 (6-chloro-3-[1-methylcyclopropyl]amino-4 H-thieno[3,2-e]-1,2,4-thiadiazine 1,1-dioxide), an adenosine triphosphate-sensitive potassium channel opener, on islet transplantation. Male inbred C57BL/6 mice were used as donors and recipients. One hundred fifty islets were isolated via collagenase digestion and density gradient, and syngeneically transplanted under the kidney capsule in mice with streptozotocin-induced diabetes. Recipients were treated with or without rofecoxib, 10 mg/kg/d orally, or with or without NN414, 3 mg/kg/d orally, for 4 weeks. After transplantation, recipient body weight, blood glucose concentration, and intraperitoneal glucose tolerance were measured. The grafted kidney was extracted for determination of insulin content at 4 weeks. In the rofecoxib-treated and NN414-treated groups and both control groups, body weight remained stable, and the blood glucose concentration decreased progressively. However, at 4 weeks after transplantation in the groups treated or not treated with rofecoxib or NN414, no significant difference was observed in recipient body weight, blood glucose concentration, and glucose tolerance or in insulin content of the graft. These data indicate that posttransplantation treatment with rofecoxib or NN414 has no beneficial effect on transplantation outcome in diabetic mouse recipients engrafted with a marginal islet mass.

Targeting Hypertension With a New Adenosine Triphosphate–sensitive Potassium Channel Opener Iptakalim

Hypertension is the most common cardiovascular disease. The discovery of the antihypertensive action of adenosine triphosphate-sensitive potassium (K(ATP)) channel openers was a significant advance in the treatment of hypertension. Iptakalim is a novel K(ATP) channel opener with a unique chemical structure that differs from other K(ATP) openers. Among the 3 different subtypes of K(ATP) channels heterologously expressed in human embryonic kidney cells and Xenopus oocytes, iptakalim exhibits significant selectivity for SUR2B/Kir6.1 channels, mild effects on SUR2A/Kir6.2 channels, and fails to open SUR1/Kir6.2 channels. Iptakalim is a more potent activator of the SUR2B/Kir6.1 subtype of K(ATP) channels than diazoxide and pinacidil, the 2 most commonly studied K(ATP) channel openers. Iptakalim selectively produces arteriolar vasodilation with essentially no effect on the capacitance vessels. It can preferentially relax arterioles and small arteries, without affecting large arteries. Furthermore, iptakalim strongly lowers the blood pressure of hypertensive rodents and humans but has little effect on normotensive rodents and humans. Selective antihypertensive action is not observed with pinacidil or diazoxide and may be due to the high selectivity of iptakalim for the SUR2B/Kir6.1 subtype of K(ATP) channels, as well as its selective relaxation of resistance vessels. In pulmonary arterial smooth muscle cells, iptakalim inhibits the increase of cytoplasmic free Ca2+ concentration, as well as cell proliferation induced by endothelin-1. Furthermore, iptakalim has exerted protective effects against hypertensive damage to target organs in rats and improves endothelial dysfunction associated with cardiovascular diseases by selective activation of the SUR2B/Kir6.1 subtype of K(ATP) channels expressed in the endothelium. Clinical trials of iptakalim in the treatment of mild-moderate hypertension have been completed in China. In additional to strong antihypertensive efficacy, iptakalim seems to have a favorable safety and tolerability profile. Iptakalim is a promising new generation antihypertensive drug.

Adenosine triphosphate–sensitive potassium channel opener diazoxide maintains human myocyte volume homeostasis during stress

Adenosine triphosphate–sensitive potassium channel opener diazoxide maintains human myocyte volume homeostasis during stress

Prevention of cerebral vasospasm by local delivery of cromakalim with a biodegradable controlled-release system in a rat model of subarachnoid hemorrhage

One mechanism that contributes to cerebral vasospasm is the impairment of potassium channels in vascular smooth muscles. Adenosine triphosphate-sensitive potassium channel openers (PCOs) appear to be particularly effective for dilating cerebral arteries in experimental models of subarachnoid hemorrhage (SAH). A mode of safe administration that provides timed release of PCO drugs is still a subject of investigation. The authors tested the efficacy of locally delivered intrathecal cromakalim, a PCO, incorporated into a controlled-release system to prevent cerebral vasospasm in a rat model of SAH. Cromakalim was coupled to a viscous carrier, hyaluronan, 15% by weight. In vitro release kinetics studies showed a steady release of cromakalim over days. Fifty adult male Sprague-Dawley rats weighing 350-400 g each were divided into 10 groups and treated with various doses of cromakalim or cromakalim/hyaluronan in a rat double SAH model. Treatment was started 30 minutes after the second SAH induction. Animals were killed 3 days after treatment, and the basilar arteries were processed for morphometric measurements and histological analysis. Controlled release of cromakalim from the cromakalim/hyaluronan implant at a dose of 0.055 mg/kg significantly increased lumen patency in a dose-dependent manner up to 94 +/- 8% (mean +/- standard error of the mean) of the basilar arteries of the sham group compared with the empty polymer group (p = 0.006). Results in the empty polymer group were not different from those in the SAH-only group, with a lumen patency of 65 +/- 12%. Lumen patencies of the cromakalim-only groups did not differ in statistical significance at low (64 +/- 9%) or high (66 +/- 7%) doses compared to the SAH-only group. Treatment of SAH with a controlled-release cromakalim/hyaluronan implant prevented experimental cerebral vasospasm in this rat double hemorrhage model; this inhibition was dose-dependent. The authors' results confirm that sustained delivery of cromakalim perivascularly to cerebral vessels could be an effective therapeutic strategy in the treatment of cerebral vasospasm after SAH.

Potassium Channel-Related Relaxation by Levosimendan in the Human Internal Mammary Artery

Levosimendan is a potent inotropic and vasodilator drug used in the treatment of decompensated heart failure. There is no study on in vitro effects of levosimendan in human isolated arteries. We investigated the effect of levosimendan on contractile tone of human isolated internal mammary artery (IMA). The responses in IMA were recorded isometrically by a force-displacement transducer in isolated organ baths. Levosimendan was added to organ baths either at rest or after precontraction with phenylephrine (1 micromol/L). Levosimendan-induced relaxations were tested in the presence of cyclooxygenase inhibitor indomethacin (10 micromol/L), nitric oxide synthase inhibitor N122-nitro-L-arginine methyl ester (100 micromol/L), large-conductance calcium-activated potassium-channel inhibitor tetraethylammonium (1 mmol/L), adenosine triphosphate-sensitive potassium-channel inhibitor glibenclamide (10 micromol/L), and voltage-sensitive potassium-channel inhibitor 4-aminopyridine (1 mmol/L). Levosimendan (10 nmol/L to 3 micromol/L) produced potent relaxation in human IMA (maximal effect, 75.3% +/- 4.9% of phenylephrine maximum contraction, 6.8 +/- 0.1, n = 15; -log10 of 50% effective concentration). Vehicle had no significant relaxant effect. The relaxation to levosimendan is not affected by either potassium-channel inhibitors (tetraethylammonium and 4-aminopyridine) or cyclooxygenase and nitric oxide synthase inhibitors. Glibenclamide (10 micromol/L) inhibited levosimendan-induced relaxation significantly (p < 0.01). Levosimendan effectively and directly decreases the tone of IMA. The mechanism of levosimendan-induced relaxation in IMA appears in part to be adenosine triphosphate-sensitive potassium-channel opening action. Levosimendan may be a cardiovascular protective agent by its relaxing action on the major arterial graft, IMA.

Pinacidil improves contractile function and intracellular calcium handling in isolated cardiac myocytes exposed to simulated cardioplegic arrest

Background We examined the effects of pinacidil on contractile function and intracellular calcium in isolated rat cardiomyocytes exposed to cardioplegic solution. Methods Rat myocytes were incubated at 24°C for 2 hours in cardioplegic solution with or without pinacidil (50 μmol/L), then they were perfused with Krebs-Henseleit solution with a gas phase of 95% O 2/5% CO 2 at the same temperature. Contraction and intracellular calcium transients were then measured by video tracking and spectrofluorometry. Results During 20 minutes of perfusion after 2 hours in cardioplegic solution with pinacidil, (1) the recovery of contractile function was significantly increased in terms of both amplitude of contraction (98.30% ± 9.90% versus 81.00% ± 11.25%; p < 0.05) and peak velocity of cell shortening (100.90% ± 13.79% versus 76.89% ± 18.14%; p < 0.01) when compared with myocytes in cardioplegic solution without pinacidil; (2) the amplitudes of the intracellular calcium transients evoked by electrical stimulation and caffeine (10 mmol/L) increased by 23.31% to approximately 40.72% and 61.73%, respectively, compared with those in cardioplegic solution without pinacidil; and (3) the decay time of the caffeine-induced intracellular calcium transient decreased by 36.64% ± 15.10% relative to that measured in cardioplegic solution without pinacidil. The effects induced by supplementing the cardioplegic solution with pinacidil were diminished in the presence of glibenclamide (10 μmol/L). Conclusions Addition of the adenosine triphosphate–sensitive potassium-channel opener, pinacidil, to a high potassium cardioplegic solution improves recovery of contractile properties and cytosolic calcium in isolated rat cardiac myocytes.

Potassium Channels and Human Corporeal Smooth Muscle Cell Tone: Diabetes and Relaxation of Human Corpus Cavernosum Smooth Muscle by Adenosine Triphosphate Sensitive Potassium Channel Openers

Potassium Channels and Human Corporeal Smooth Muscle Cell Tone: Diabetes and Relaxation of Human Corpus Cavernosum Smooth Muscle by Adenosine Triphosphate Sensitive Potassium Channel Openers

Potassium Channels and Human Corporeal Smooth Muscle Cell Tone: Diabetes and Relaxation of Human Corpus Cavernosum Smooth Muscle by Adenosine Triphosphate Sensitive Potassium Channel Openers

Sustained contraction of human corporeal smooth muscle depends on continuous transmembrane calcium flux through voltage gated calcium channels. K channels modulate corporeal smooth muscle membrane potential and, thus, ultimately affect transmembrane calcium flux. Therefore, we characterized relaxation responses elicited by the K channel modulators pinacidil and levcromakalim on isolated human corporeal tissue strips. We also evaluated the possibility that there may be alterations in adenosine triphosphate sensitive K channel pharmacology/function related to the presence of diabetes mellitus. A total of 215 isolated human corporeal tissue strips obtained from 57 male patients with organic erectile dysfunction were investigated. Cumulative concentration-response curves were constructed at half log increments for steady state relaxation responses elicited by pinacidil and levcromakalim on equivalently phenylephrine pre-contracted (to approximately 75% of maximum) isolated corporeal tissue strips. Potassium currents were measured using the cell attached whole cell patch clamp technique on freshly isolated corporeal smooth muscle cells. A concentration dependent, glibenclamide sensitive relaxation response of phenylephrine pre-contracted corporeal tissue strips was observed for pinacidil and levcromakalim. Consistent with such observations, electrophysiological recordings on freshly isolated myocytes revealed that pinacidil (10 microM.) and levcromakalim (10 microM.) induced whole cell potassium currents that were blocked by glibenclamide (10 microM.). In addition, statistical analysis revealed that phenylephrine pre-contracted corporeal tissue strips from patients without diabetes were more sensitive to relaxation by both compounds than corporeal tissue strips excised from those with diabetes. Furthermore, relaxation responses elicited by pinacidil and levcromakalim were not affected by charybdotoxin or 4-aminopyridine but were completely reversed by KCl or tetraethylammonium chloride. These data indicate that the adenosine triphosphate sensitive K channel subtype is likely to have an important role in the relaxation of isolated corporeal tissue strips and, moreover, they are the molecular target for the K channel modulators/openers levcromakalim and pinacidil. Such observations are consistent with the supposition that alterations in the structure/function/activity of these potassium channels may underlie at least some aspects of observed diabetes related differences in tissue sensitivity to K channel modulators.

Effect of Adenosine Triphosphate–Sensitive Potassium Channel Openers on Lung Preservation

ATP-sensitive potassium channel (KATP) openers have been proven to be involved in ischemic preconditioning, which protects ischemic tissue. However, the effect of KATP openers on ischemia-reperfusion injury of the lungs remains unknown. We investigated whether a KATP opener, pinacidil, can attenuate ischemia-reperfusion injury using an ex vivo rat lung model. Heart-lung blocks were flushed and preserved with phosphate-buffered saline (control group) or with one of the solutions containing pinacidil (pinacidil group) or pinacidil + glibenclamide (a KATP blocker) (glibenclamide group). The control and glibenclamide groups showed significantly higher values with respect to shunt fraction, pulmonary arterial pressure, and peak inspiratory pressure than the pinacidil group. The concentrations of total adenine nucleotides and ATP in the lung after reperfusion became significantly lower in the control and glibenclamide groups than in the fresh group. Lipid peroxidation of the lungs increased significantly in the control and glibenclamide groups after reperfusion. State 3 mitochondrial respiration and State 3/4 ratios of mitochondrial respiration were significantly decreased in the lungs of the control and glibenclamide groups. These findings suggested that KATP openers would maintain the mitochondrial respiratory function during lung preservation, prevent lipid peroxidation after reperfusion, and attenuate ischemia-reperfusion injury.

Effect of mild hypothermia on nicorandil-induced vasodilation of pial arterioles in cats

Nicorandil is characterized as hybrid between nitrates and potassium channel activators. Recent evidence suggested that mild hypothermia may alter cerebral vasodilation induced by a nitrate agent and potassium channel opener. However, the effect of mild hypothermia on nicorandil-induced vasodilation is not known. The present study was conducted to investigate whether mild hypothermia could alter nicorandil-induced cerebral vasodilation. In addition, the effects of mild hypothermia on cerebral vasodilation induced by nitroglycerin, a nitrate agent, and cromakalim, a selective adenosine 5'-triphosphate-sensitive potassium channel opener, were assessed in the same model. Prospective, randomized, experimental study with repeated measures. Investigational animal laboratory. Twenty-four cats. Animals were anesthetized with pentobarbital. The cranial window technique, combined with microscopic video recording, was used to measure small (50-100 microm) and large (100-200 microm) pial arteriolar diameter in an experiment. Animals were assigned randomly to either a normothermic (37 degrees C) or a hypothermic (33 degrees C) group. Nicorandil, nitroglycerin, or cromakalim at concentrations of 10(-8), 10(-6), or 10(-4) mol/L was applied topically in the cranial window, and the diameter of pial arterioles was measured. Topical administration of nicorandil, nitroglycerin, and cromakalim significantly dilated both small and large pial arterioles in a dose-dependent manner during normothermia. Nicorandil-induced vasodilation of either large or small pial arterioles was not affected by hypothermia. However, hypothermia significantly attenuated nitroglycerine-induced vasodilation in both large and small pial arterioles and enhanced cromakalim-induced vasodilation in both large and small pial arterioles. Nicorandil-induced vasodilation of cerebral pial arterioles was not affected by mild hypothermia. By contrast, mild hypothermia significantly attenuated nitroglycerin-induced vasodilation and enhanced cromakalim-induced vasodilation.

The adenosine triphosphate–sensitive potassium channel opener nicorandil protects the ischemic rabbit spinal cord

Objective: We investigated the protective effects of an adenosine triphosphate–sensitive potassium channel opener nicorandil in the rabbit model of spinal cord ischemia. Methods: Rabbits were randomized into 4 groups (each n = 6): the nicorandil group (100 μg/kg intravenous nicorandil 10 minutes before ischemia); the glibenclamide plus nicorandil group (3 mg/kg intravenous glibenclamide, an antagonist of adenosine triphosphate–sensitive potassium channels, 10 minutes before nicorandil administration); the vehicle group (vehicle alone); and the sham operation group (without spinal cord ischemia). Spinal cord ischemia was induced by balloon occlusion of the infrarenal abdominal aorta for 15 minutes at 39°C. Neurologic function was graded into Johnson&'s score at 8 hours, 1 day, and 2 days. Histopathologic examination was performed at 2 days, and the number of intact motor neuron cells was compared. Results: Johnson scores of the glibenclamide plus nicorandil and vehicle groups were significantly lower than those of the sham operation and nicorandil groups at each time point, and no statistically significant difference was observed between the glibenclamide plus nicorandil and vehicle groups. Histopathologic examination revealed that motor neurons were almost normal in the nicorandil group, whereas about 55% of motor neurons were lost in the vehicle and glibenclamide plus nicorandil groups. Conclusions: Nicorandil has a protective effect on the ischemic rabbit spinal cord, and the beneficial effect seems mediated through the activation of adenosine triphosphate–sensitive potassium channels.

Diazoxide protects mitochondria from anoxic injury: Implications for myopreservation

Background: Heart muscle primarily relies on adenosine triphosphate produced by oxidative phosphorylation and is highly vulnerable to anoxic insult. Although a number of strategies aimed at improving myopreservation are available, no effective means of preserving mitochondrial energetics under conditions of anoxic injury have been developed. Openers of mitochondrial adenosine triphosphate–sensitive potassium channels have emerged as powerful cardioprotective agents presumably capable of maintaining mitochondrial function under metabolic stress. Here, we evaluated the ability of a prototype mitochondrial adenosine triphosphate–sensitive potassium channel opener, diazoxide, to preserve oxidative phosphorylation in mitochondria subjected to anoxia and reoxygenation. Methods: Mitochondria were isolated from rat hearts and subjected to 20 minutes of anoxia, followed by reoxygenation. Mitochondrial respiration and oxidative phosphorylation, as well as mitochondrial integrity, were assessed by means of ion-selective minielectrodes, high-performance liquid chromatography, fluorometry, and electron microscopy. Results: Anoxia-reoxygenation decreased the rate of adenosine diphosphate–stimulated oxygen consumption, inhibited adenosine triphosphate production, and disrupted mitochondrial integrity. On average, anoxic stress reduced adenosine diphosphate–stimulated respiration from 291 ± 14 to 141 ± 15 ng-atoms O2 · min–1 · mg–1 protein and decreased the rate of adenosine triphosphate production from 752 ± 14 to 414 ± 34 nmol adenosine triphosphate · min–1 · mg–1 protein. After anoxia, the majority (88%) of mitochondria was damaged or swollen and released adenylate kinase, a marker of mitochondrial integrity. Diazoxide (100 μmol/L), present throughout anoxia, preserved adenosine diphosphate–stimulated respiration at 255 ± 7 ng-atoms O2 · min–1 · mg–1 protein and adenosine triphosphate production at 640 ± 39 nmol adenosine triphosphate · min–1 · mg–1 protein. Diazoxide also protected mitochondrial structure from anoxia-mediated damage, so that after anoxic stress, 67% of mitochondria remained intact and adenylate kinase was confined to the mitochondria. Conclusions: The present study demonstrates that diazoxide diminishes anoxia-induced functional and structural deterioration of cardiac mitochondria. By protecting mitochondria and preserving myocardial energetics, diazoxide may be useful under conditions of reduced oxygen availability, including global surgical ischemia or storage of donor heart. (J Thorac Cardiovasc Surg 2001;121:298-306)

Donor heart preservation with a novel hyperpolarizing solution: Superior protection compared with University of Wisconsin solution

Objectives: A donor heart preservation solution was designed to use hyperpolarized arrest with the adenosine triphosphate–sensitive potassium-channel opener pinacidil. This solution contained concentrations of potassium, sodium, calcium, magnesium, lactobionate, and the buffer histidine specifically chosen to minimize intracellular calcium accumulation associated with prolonged ischemia. Methods: Twenty-four rabbit hearts were randomly assigned to receive 1 of 3 preservation solutions in a crystalloid-perfused Langendorff model: (1) prototype solution containing a 0.5 mmol/L concentration of pinacidil, (2) prototype solution without pinacidil as control, and (3) University of Wisconsin solution. Thirty minutes of initial perfusion preceded baseline data acquisition. Data comprised left ventricle pressure-volume curves generated by inflating an intraventricular latex balloon. After cardioplegic administration, hearts underwent 4 hours of hypothermic storage, followed by 60 minutes of reperfusion and postischemic data acquisition. Results: Postischemic developed pressure was better preserved by pinacidil solution (92.4% ± 4.5%) than by the control (74.9% ± 3.4%, P = .01) and University of Wisconsin solutions (66.7% ± 5.1%, P = .001). Diastolic negative dP/dT was better preserved by pinacidil solution (104.4% ± 10.2%) than by the control (80.2% ± 4.2%, P = .034) and University of Wisconsin solutions (71.7% ± 7.0%, P = .015). Diastolic compliance, expressed as baseline/postischemic diastolic slope ratios, was more poorly preserved by University of Wisconsin solution (0.67 ± 0.07) than by the pinacidil (0.88 ± 0.05, P = .041) and control solutions (0.87 ± 0.05, P = .021). Postischemic coronary flow was higher in hearts exposed to pinacidil solution (77.8% ± 3.0%) than in those exposed to the control (66.8% ± 2.4%) and University of Wisconsin solutions (70.9% ± 4.0%, P = .07). Conclusions: The superiority of the pinacidil solution in this experiment demonstrated that hyperpolarized arrest with potassium-channel openers improves donor heart preservation when administered in a novel histidine-buffered lactobionate-enriched vehicle. (J Thorac Cardiovasc Surg 2000;120:746-54)

Regulation of coronary myoplasmic Ca2+-myosin light chain phosphorylation pathway and vasomotor tone: Hyperpolarizing versus depolarizing cardioplegia

Background: This study was designed to compare the effects of hyperpolarizing versus depolarizing cardioplegic solutions on the coronary vasomotor regulation, specifically focusing on coronary myoplasmic Ca2+-myosin light chain (MLC) phosphorylation pathway and β-adrenergic signal transduction. Methods: With the use of an in vitro cardioplegic model, rat coronary microvessels loaded with fura-2 were subjected to simulated cold (20°C) cardioplegia and reperfused with Krebs solution for 60 minutes at 37°C. Cardioplegia consisted of either (1) Krebs solution alone (control), (2) Krebs plus adenosine triphosphate–sensitive potassium channel opener (100 μmol/L pinacidil [PCO-CP]), (3) hyperkalemic cardioplegia (K+ = 25 mmol/L [K-CP]), or (4) K-CP plus magnesium (Mg2+ = 25 mmol/L; [K/Mg-CP]). Results: At the endpoint of the cardioplegic period, K-CP resulted in a significant increase both in [Ca2+]i and in MLC phosphorylation compared with control (both P <.05). In contrast, PCO-CP did not make any significant difference in these indices compared with control. After reperfusion, the relaxation responses to isoproterenol and forskolin after K-CP were significantly reduced (both P <.05 vs control) but were preserved after PCO-CP. K/Mg-CP provided comparable effects to PCO-CP. Conclusions: These results suggest that neither an activation of the coronary myoplasmic Ca2+-MLC phosphorylation pathway nor β-adrenergic desensitization seen after exposure to depolarizing cardioplegia occurs with exposure to hyperpolarizing cardioplegia and magnesium-supplemented depolarizing hyperkalemic cardioplegia. (Surgery 2000;128:185-91.)

Pharmacological preconditioning with the adenosine triphosphate–sensitive potassium channel opener pinacidil

Background. Ischemic preconditioning (IPC) decreases infarct size after global or regional ischemia. Potassium channel openers also precondition but are subject to dose-limiting vasodilation. We compared the mechanical and electrophysiological effects of ischemic and pharmacological preconditioning in an isolated rabbit heart model. Methods. Rabbit hearts were preconditioned with either 10 μmol/L pinacidil alone (P−), 10 μmol/L pinacidil with 10 μmol/L phenylephrine (P+), or two cycles of global ischemia and reperfusion (IPC) before 1 hour of LAD occlusion. Left ventricular pressure, epicardial monophasic action potential duration (APD) and coronary flow were monitored throughout. Infarct size was determined at the end of reperfusion. Results. Regional ischemia uniformly decreased APD ( p < 0.05). During reperfusion, APDs were prolonged beyond preischemic values in all preconditioned groups ( p < 0.05). P− and P+ reduced the incidence of fibrillation. P− significantly increased coronary flow (+15%, p = 0.001), whereas IPC and P+ did not. However, IPC and P− significantly decreased systolic function ( p < 0.05) but P+ did not. In addition, IPC depressed diastolic function ( p < 0.05) but P− and P+ did not. Infarct size was reduced by all methods ( p < 0.05). Conclusions. Pinacidil presents a safe and effective alternative to IPC for preserving the heart during regional ischemia. Its coronary vasodilatory effects are safely and effectively reversed by the addition of phenylephrine.

Selective mitochondrial adenosine triphosphate–sensitive potassium channel activation is sufficient to precondition human myocardium

Objectives: Recently, the mitochondrial adenosine triphosphate–sensitive potassium channel has been suggested to be the final common effector of myocardial preconditioning. The purpose of this study is to determine whether selective mitochondrial adenosine triphosphate–sensitive potassium channel activation alone can precondition human myocardium from an ischemia/reperfusion insult. Methods: Isolated human right atrial trabeculae were placed in tissue baths, paced, and subjected to 30 minutes of normothermic hypoxia (ischemia) followed by 45 minutes of reoxygenation (reperfusion). Trabeculae were preconditioned with a selective mitochondrial adenosine triphosphate–sensitive potassium channel opener (diazoxide 30 μmol/L) or a nonselective purinergic agonist, adenosine (125 μmol/L), for 5 minutes (adenosine) followed by a 10-minute washout period. Developed force at end reperfusion (mean ± standard error) was compared with baseline, and tissue creatine kinase and adenosine triphosphate levels were measured after ischemia/reperfusion. Results: Trabeculae subjected to ischemia/reperfusion exhibited 30% ± 2% of baseline developed force, whereas trabeculae subjected to selective adenosine triphosphate–sensitive potassium channel opening (diazoxide) and nonselective purinergic agonist (adenosine) recovered to 55% ± 7% and 46% ± 3% of baseline developed force, respectively. Tissue creatine kinase activity was preserved in both the diazoxide- and adenosine-treated trabeculae (5.4 ± 12 and 5.4 ± 14 μmol/L per gram wet tissue) compared with ischemia/reperfusion (1.8 ± 0.2 U/mg wet tissue). Adenosine triphosphate levels at end reperfusion were also increased in the trabeculae treated with selective (diazoxide) and nonselective (adenosine) adenosine triphosphate–sensitive potassium channel opener (4.1 ± 0.01 and 4.4 ± 0.2 μmol/L per gram wet tissue) compared with trabeculae subjected to ischemia/reperfusion (1.5 ± 0.1 μmol/L per gram wet tissue). Conclusions: These results suggest that selective mitochondrial adenosine triphosphate–sensitive potassium channel activation preconditions human myocardium and the protection conferred is equal to that of adenosine preconditioning. Targeted openers of mitochondrial adenosine triphosphate– sensitive potassium channels promote constructive protection of myocellular energy levels, contractile function, and cellular viability in human myocardium after ischemia/reperfusion. (J Thorac Cardiovasc Surg 2000;120:387-92)

Protection of the myocardial cell during ischemia

Prevention of myocardial necrosis in acute coronary syndromes is the immediate goal of therapy. Decreasing myocardial oxygen needs is of marginal value. Improving oxygen delivery by mechanical or thrombolytic reperfusion is more successful but still leaves much to be desired in terms of time to reperfusion before damage occurs due to reperfusion itself. During ischemia, there is a metabolic mismatch between glycolysis and glucose oxidation that results in accumulation of hydrogen ions, which, in turn, activates the Na +/H + exchange system (NHE-1), leading to Na + and Ca 2+ overload and cell death. Blocking NHE-1 is a new strategy designed to prevent or delay cell death. Cariporide, a potent inhibitor of the NHE-1 system, is currently under investigation. Other agents under investigation are designed to modify proton generation, modify proton effects, and attenuate necrosis progression. Also under study are agents designed to mediate preconditioning (adenosine agonists and adenosine triphosphate–sensitive potassium channel openers). Other approaches to minimize cell injury include use of antioxidants and free-radical scavengers, complement inhibitors, selectin blockers, and glycoprotein (GP) IIb/IIIa antagonists.