Effects of Endothelium-derived Relaxing Factors on the Regulation of ATP-sensitive Potassium Channel Activity in Cardiac Myocytes

BACKGROUND AND OBJECTIVES: Effects of the three major endothelium-derived relaxing factors (EDRFs), namely nitric oxide (NO), prostacyclin (PGI2), and 11, 12-epoxyeicosatrienoic acid (EET) on the ATP-sensitive potassium channel (K ATP channel) activity were examined in isolated cardiac ventricular myocytes. MATERIALS AND METHODS: K ATP channel activities were measured in the enzymatically (collagenase) isolated single mouse ventricular myocytes using excised inside-out, cell-attached, and perforated whole-cell patch clamp techniques. RESULTS: In inside-out patches, NO donors, SNP and spermine NONOate, did not affect the K ATP channel activity. In the presence of both ATP and ADP in the bath solution, the NO donors attenuated the activity of the K ATP channel. In cell-attached patches, the NO donors potentiated pinacidil-induced K ATP channel activity. In perforated whole-cell patch configuration, the NO donors decreased the K ATP current induced by PCO 400, a K ATP channel opener. PGI2 did not affect the K ATP channel activity in excised insideout patch. However, in the pres-ence of ATP in the internal solution, PGI2 increased the channel activity in a dose-dependent manner. In cell-attached patches, PGI2 did not only affect the channel activity itself, but also the dinitrophenol-induced K ATP channel activity. 11, 12-EET had no effect on K ATP channel activities.CONCLUSION: These results indicate that some of the endothelium-derived relaxing factors (nitric oxide and prostacyclin) are involved in the regulation of ATP-sensitive potassium channel activities in mouse ventricular myocytes; and the regulation type was com-plicated, activation or inhibition, depending on the cellular environment.

Effect of Maturation on Endothelium-Dependent Relaxation in Pulmonary Arteries of the Newborn Rabbit

PURPOSE: This study was done to determine whether maturatin alters endothelium- dependent responses in pulmonary arteries. METHODS: Vascular rings of pulmonary arteries, with and without endothelium, taken from rabbits of 3 and 30 days of age were suspended in organ chambers filled with Krebs-Henseleit solution, bubbled with 95% O2-5% CO2 and maintained at 37degrees C. Immediately after mounting, the rings were stretched progressively until a maximal response to KCl was achieved. The rings were incubated with indomethacin and allowed to equilibrate before contraction and relaxation study. RESULTS: When the endothelium was intact in arterial rings from 3-day-old rabbits, acetylcholine (ACH) (10-6 M) relaxed preconstricted rings with histamine (5x10-6 M) (98.1 4.7% relaxation, mean SD). In rings without endothelium, KCl (10-2 to 9x10-2 M) and histamine (5x10-8 to 10-5 M) caused concentration-dependent contractions. When normalized to maximal contractions achieved to each agonist, the concentration-effect curves to KCl and histamine in rings without endothelium were similar to both ages. Rings with endothelium showed a progressive shift to the right of the concentration- effect curve to histamine. Relaxation to sodium nitroprusside were unaffected by age. In preconstricted ring, ACH (10-8 to 5x10-6 M) caused relaxations in rings with endothelium which were greater at 30-day compared to 3-day-old rabbits. CONCLUSION: These study demonstrates that endothelium-dependent relaxation increase with age, possibly due to changes in the release and/or effect of endothelium-derived relaxing factor (EDRF or nitric oxide) from pulmonary arteries during the neonatal period.

Effects of Propofol on Hypoxic Pulmonary Vasoconstriction after Pretreatment with L-NAME and Glibenclamide in Isolated Rat Lungs / 대한마취과학회지

BACKGROUND: It is generally accepted that propofol does not inhibit hypoxic pulmonary vasoconstriction (HPV). However, because the previous studies for the effects of propofol on HPV were established in vivo, the effects of physiologic variables could not be ruled out. Therefore, we investigated the effects of various concentrations of propofol on HPV at isolated rat lungs and the relationship of these effects of propofol on HPV and endothelium-derived relaxing factor (EDRF) and an ATP-dependent K+ channel which were candidates as the mechanism of HPV. METHODS: In 30 isolated rat lungs, after three hypoxic challenges for 5 minutes, we administered saline in the control group, N(G)-nitro-L-arginine methyl ester (L-NAME) in the L group and glibenclamide in the G group followed by three hypoxic challenges for 5 minutes. In addition, we studied the effects of various concentrations of propofol on HPV in the three groups. RESULTS: L-NAME and glibenclamide did not alter baseline pulmonary arterial pressure but L-NAME significantly enhanced HPV. Clinical concentrations of propofol did not affect HPV and high concentrations of propofol inhibited HPV. The pretreatment of L-NAME and glibenclamide did not alter the inhibition of HPV even at high concentrations of propofol. CONCLUSIONS: The EDRF and ATP-dependent K+ channel did not largely contribute to baseline pulmonary arterial tone but EDRF might be released and downregulate HPV. Clinical concentrations of propofol did not inhibit HPV but high concentrations of propofol inhibited HPV. In addition, the mechanism of inhibition of HPV at high concentrations of propofol did not relate to the EDRF pathway and ATP-dependent K+ channel.

Effects of nitric oxide forming enzyme inhibitor on hypoxic pulmonary vasoconstriction in endurance exercise-trained perfused rat lungs / 体力科学

Previously, we observed that hypoxic pulmonary vasoconstriction (HPV) can be reduced by endurance exercise training. This study determined whether nitric oxide (NO) plays a role in inhibition of the HPV after endurance exercise training in isolated rat lung perfused with physiological saline solution containing meclofenamate. Sprague-Dawley rats were used, and were divided into two groups: a control (Cont) group and an endurance exercise-trained (ET) group. Endurance exercise training was carried every day on a small-animal motorized treadmill. The training protocol was 30 to 40 min/day and the rats ran at a speed of 15 to 30 m/min for 2 weeks. It appeared that HPV could be reduced by short-term endurance exercise training. The NO-forming enzyme inhibitor, N<SUP>G</SUP>-nitro-L-arginine methyl ester (1.5×10<SUP>-8</SUP>M, L-NAME), administered to the ET group increased the HPV compared in that of the Cont group. These findings indicate that endothelial NO synthesis may contribute to the inhibition of HPV in ET rats. Our data suggest that endurance exercise training promotes endothelium dependent-pulmonary vasodilation through the stimulation of NO released during HPV.

The Pulmonary Hemodynamic Effects of Nitric Oxide Inhalation on Hypoxic Pulmonary Vasoconstriction / 대한마취과학회지

BACKGROUND: Nitric Oxide (NO) has been discovered to be an important endothelium-derived relaxing factor. The exogenous inhaled NO may diffuse from the alveoli to pulmonary vascular smooth muscle and produce pulmonary vasodilation, but any NO that diffuses into blood will be inactivated before it can produce systemic effects. To examine the effects of NO on pulmonary and systemic hemodynamics, NO was inhaled by experimental dogs in an attempt to reduce the increase in pulmonary artery pressure (PAP) and pulmonary vascular resistance (PVR) induced by hypoxia in dogs. METHODS: Eight mongrel dogs were studied while inhaling 1)50% O2 (baseline), 2)12% O2 in N2 (hypoxia), 3)followed by the same hypoxic gas mixture of O2 and N2 containing 20, 40 and 80 ppm of NO, respectively. RESULTS: Breathing at FIO2 0.12 nearly doubled the pulmonary vascular resistance from 173 56dyn sec cm-5 to 407 139dyn sec cm-5 and significantly increased the mean pulmonary artery pressure from 16 3mmHg to 22 4mmHg. After adding 20~80 ppm NO to the inspired gas while maintaining the FIO2 at 0.12, the mean pulmonary artery pressure decreased (p<0.05) to the level when breathing oxygen at FIO2 0.5 while the PaO2 and PaCO2 were unchanged. The pulmonary vascular resistance decreased significantly and the right ventricular stroke work index returned to a level similar to breathing at FIO2 0.5 by addition of NO into the breathing circuit. Pulmonary hypertension resumed within 3~5 minutes of ceasing NO inhalation. In none of our studies did inhaling NO produce systemic hypotension and elevate methemoglobin levels. CONCLUSIONS: Inhalation of 20~80 ppm NO selectively induced pulmonary vasodilation and reversed hypoxic pulmonary vasoconstriction without causing systemic vasodilation and bronchodilation. Methemoglobin and NO2 were within normal limit during the study.

Phorbol Ester Modulates th Action of Acetylcholine in Rabbit Carotid Artery

Authors studied the regulatory mechanism of protein kinase C on the action of acetylcholine in rabbit carotid artery. The arterial rings were myographied isometrically in an isolated organ bath. In this study, acetylcholine relaxed phenylephrine-induced contraction of rabbit carotid artery in the presence of endothelium. In the pretreatment of methylene blue or nitro-L-arginine, the action of acetylchioline was reduced. Pretreatment of phorbol 12-myristate 13-acetate(PMA) attenuated the action of acetylcholine, but PMA did not attenuated it in the presence of staurosporine, suggesting that protein kinase C suppressed the action of acetylcholine. The potency of phorbol ester on the action of acetylcholine was PMA>phorbol 12, 13-dibutyrate(PDBu)>phorbol 12,13-diacetate(PDA), but the direct effect of phorbol on the contraction of arterial rings was PDBu>PMA>PDA. This implied that protein kinase C involved in the contraction of smooth muscle and the attenuation of the action of acetylcholine were different. PMA did not affect on A23187- and sodium nitroprusside-induced vasorelaxation. Acetylcholine increased tissue cGMP contents, which was reduced by PMA. These results suggest that in rabbit carotid artery protein kinase C reduce acetylcholine-stimuated endothelium derived relaxing factor(EDRF) release by affecting membrane receptor, and do not affect on the function of EDRF and cGMP production in the smooth muscle.

Role of Endothelium -Derived Relaxing Factor in the Pathogenesis of Coronary Artery Spasm and Its Relationship with Ethanol

Isometric tension recording was performed in the transverse strips of porcine coronary arteries and rabbit aorta to observe the effects of the endothelium and endothelium-derived relaxing factor(EDRF) on vasomotor tone and to test the hypothesis that alcohol may have the deleterious effect on endothelium-dependent vasorelaxation. Tension-development by vasoconstrictor was markedly attenuated in the endothelium-intact strips compared to the endothelium denuded strips. Administration of hemoglobin(10-5M) to inhibit the action of EDRF increased tension selectively in the endothelium-infarct strips, which is suggestive of basal EDRF secretion. Nitro L-arginine(10-5M). an analogue of L-arginine(10-4M) partially reversed the inhibitory effect of nitro L-arginine. Ethyl alchol inhibited bradykinin-induced endothelium-dependent vasorelaxation of porcine coronary artery in dose dependent manner. These data suggest that the protective effect of vascular endothelium to the action of vasoconstirctor can be explained by exercise of basal EDRF release and damaged endothelium would be a great risk of induction of vasospasm. Also we believe that there is a relationship of competive inhibition between L-arginine. a precursor of EDRF, and its analogues on the action of EDRF and alcohol intake would be hazardous to the patients with coronary artey disease because its inhibitory action on endothelium-dependent vasorelaxation may evoke myocardial ischemia.

Contractile and Inhibitory Effects of McN-A-343 and Acetylcholine on Isolated Arteries

Effect of acetylcholine(ACh) and McN-A-343 on porcine coronary artery and rabbit thoracic aorta were investigated in isolated preparations with or without intact endothelium. In the porcine coronary artery, ACh produced concentration dependent contraction which was greater in rings without the endothelium than in intact endothelial rings, but McN-A-343 did not alter the basel tension in both tissues. ACh relaxed contraction induced by 5-hydroxytryptamine(5-HT) in only intact endothelial rings, while NcN-A-343 inhibited the 5-HT induced tension in both preparations dose dependently. Carbachol elicited a prominent contraction in both tissues. The carbacol-induced tension was markedly inhibited by McN-A-343 in either rings with or without endothelium, while ACh contracted further the tension. ACh and McN-A-343 did not after the KCi induced tension, but clearly potentiated the contraction induced by Bay K 8644 in intact endothelial rings. In rabbit thoracic aorta, ACh elicited contraction in a concentration-dependent fashion which was potentiated by removal of endothelium, but McN-A-343 did not affect the basal tension of both rings. ACh inhibited the 5-HT-induced contraction in only intact endothelial ring, but McN-A-343 did not change the contraction of both rings. Conclusively, ACh produces endothelium-dependent relaxation in both arteries, while McN-A-343 elevated endothelium-independent inhibition to 5-HT or carbachol-induced tension.

Endothelium-derived hyperpolarizing factor / 中国药理学通报

There is another factor involving in endothelium dependent relaxation besides NO, which is independent of cGMP, EDHF. Its hyperpolarization mechanism may be related to the open of calcium dependent K + channels(K + Ca). NO, PGI 2,H 2O 2 and cytochrome P450 derived metabolite of arachidonic acid are all the candidates of EDHF. In the normal blood vessels, the influence of EDHF on endothelium dependent relaxation is little. But in some diseases, when the production and effect of NO is disturbed ,the mechanism of EDHF may play a specially important role.

Function and Modulation of Coronary Endothelium in Isolated lschemic-reperfused Rat Hearts / 第二军医大学学报

Isolated perfused rat hearts were subjected to regional ischemia followed by reperfusion and then tested for responsiveness to acetylcholine (Ach) and nitroglycerin (NTG). The effects of L-Arginine (L-Arg) and NG-monomethyl-L-Arg (L-NMMA) on the endothelium-dependent (ED) and independent (EI) vasodilator were also observed. It was found that both 15 and 30min ischemia followed reperfusion resulted in a decrease in ED vasodilation of Ach. ED vasodilation gradually renewed after 90min reperfusion in the 15min ischemic group, not in the 30min ischemic group. No significant decrease in EI vasodilation of NTG in all groups. L-Arg accelerated the renewing of ED vasodilation of Ach in the 15 min ischemia-reperfusion group, not in the 30min ischemia-reperfusion group. L-NMMA was an inverse action. The results indicate that brief ischemia followed by reperfusion can induce coronary endothelium dysfunction which may be related to the decrease of endothelium derived relaxing factor.