Expression of pancreatic ATP-sensitive K~+ channels in rats with chronic pancreatitis and drug interventions / 中华肝胆外科杂志

Objective To observe the expression of pancreatic K_(ATP) channels (Kir6.2/SUR1) in rats with chronic pancreatitis and explore the intervention of nateglinide on the changes.Methods Wistar rats were induced to suffer from chronic pancreatitis and then randomized into model group, nateglinide group and control group.Then OGTT of them were observed.RT-PCR was used to detect the expression of Kir6.2 and SUR1 mRNA, and western blot to detect the expression of Kir6.2 and SUR1 proteins.Results Model rats displayed impaired glucose tolerance (IGT).The expression of Kir6.2 and SUR1 in model group decreased significantly(P＜0.05), and nateglinide displayed up-reg-ulation to the expression in some degree.Conclusion The expression of pancreatic K_(ATP) channels in rats with chronic pancreatitis diminished, which might be the important mechanism of the development of pancreatogenic diabetes.Nateglinide can up-regulate the expression in some degree, which indicates that it may have latent effect of ameliorating the prognosis of patients with chronic pancreatitis.

K(ATP) channel / 한양의대학술지

Pharmacological preconditioning with volatile anesthetics is a phenomenon whereby a brief exposure to volatile anesthetic agents protects the heart from the potentially fatal consequences of a subsequent prolonged period of myocardial ischemia and reperfusion. Although not completely elucidated, the cellular and molecular mechanisms of pharmacological preconditioning appear to mimic those of ischemic preconditioning, the most powerful endogenous cardioprotective mechanism. Activation of ATP-dependent potassium (K(ATP)) channels in the myocardium plays an important cardioprotective role during ischemia. This article reviews current concepts and controversies regarding the specific roles of the mitochondrial and the sarcolemmal K(ATP) channels in pharmacological preconditioning by volatile anesthetics.

The Effect of Nicorandil on the Pharmacodynamics of Rocuronium / 대한마취과학회지

BACKGROUND: Some investigators have shown that nicorandil, a K(ATP) channel opener, depresses the neuromuscular transmission contraction of the skeletal muscle. However, others have reported that it improves the recovery of vecuronium relaxation and the myotonic activity of muscle. This study investigated the effect of nicorandil on rocuronium relaxation. METHODS: Hemidiaphragm-phrenic nerve preparations were obtained from male Sprague-Dawley rats (150-250 g). The preparations were bathed in Krebs' solution containing in (mM): NaCl 118, KCl 5, CaCl2 2.5, NaHCO3 30, KH2PO4 1, MgCl2 1 and glucose 11. The preparations were, then maintained at 32 degrees C and aerated with a mixture of 95% O2 and 5% CO2. Isometric forces that were generated in response to 0.1 Hz, and, 50 Hz for 1.9 seconds with supramaximal electrical stimulation (0.2 msec, rectangular) to the phrenic nerve were measured using a force transducer. The single twitch tension (ST) and peak tetanic tension (PTT) were calculated as % inhibition of the control, and the tetanic fade (TF), as % increase in the PTT. Each preparation was exposed to one of the 6 nicorandil concentrations (0.0, 0.625, 1.25, 2.5, 5, 10 micrometer), and the adequate volume of the rocuronium solution was cumulatively added to the tissue bath for a desired rocuronium concentration until there was an 80-90% decrease in the ST. The effect of rocuronium at each concentration was allowed to reach a steady state before the tension parameters were measured. The EC5, EC25, EC50, EC75, and EC95 of rocuronium for the ST, PTT and TF were calculated using a probit model. The differences between the EC50 of rocuronium according to the nicorandil concentrations were tested using a t-test and a Bonferroni's correction. RESULTS: 1.25 and 2.5 micrometer nicorandil shifted the cumulative concentration-response curves for the TF of rocuronium to the right. 5 and 10 micrometer nicorandil shifted the cumulative concentration-response curves for the ST of rocuronium to the left. CONCLUSIONS: Lower concentration of nicorandil may help maintain the tetanic contraction during rocuronium relaxation.

Identification of ATP-sensitive K+ Channel in an Uterine Leiomyoma Cell / 대한산부인과학회잡지

OBJECTIVE: The purpose of this study was to identify the ATP-sensitive potassium (K(ATP)) channel subtypes in uterine leiomyoma and normal myometrial cells, and to compare the difference in its expression between uterine leiomyoma and normal myometrial cells. METHODS: Fresh ten uterine leiomyomas and their adjacent normal myometrial tissues were obtained from hysterectomies that were conducted on benign diseases. With the use of reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analysis, we analysed the expression of K(ATP) channel subtypes in tissues and primary cultured leiomyoma cells. To demonstrate the K(ATP) channel activity in uterine leiomyoma cells, whole cell patch-clamp recordings were made. RESULTS: The uterine leiomyoma and normal myometrial tissues contained Kir6.1/SUR2B and Kir6.2/ SUR2B mRNAs, although the expression of SUR1 and SUR2A mRNAs were not expressed in the uterine leiomyoma and normal myometrial tissues. Primary cultured uterine leiomyoma and normal myometrial cells demonstrated same patterns. To determine the expression levels of K(ATP) channel subunits, high levels of Kir6.1, Kir6.2, and SUR2B were detected by western-blot analysis in uterine leiomyoma compared with normal myometrial tissues. K(ATP) channel currents were increased by estrogen application in uterine leiomyoma cells. CONCLUSION: These studies provide new knowledge concerning K(ATP) channels in uterine leiomyoma and normal myomtrial cells. we demonstrated uterine leiomyoma and normal myometrial tissues contained Kir6.1/ SUR2B and Kir6.2/SUR2B subunits and showed an increased expression in uterine leiomyoma compared with normal myometrial tissues. These results suggest that K(ATP) channels are important elements in growth of uterine leiomyoma.

Effects of K+ Channel Opener WAY120491 on Renal Function in Rabbits / 대한신장학회잡지

BACKGROUND: K+ channel opener has been considered as a vasorelaxing agent working through hyperpolarization of vascular smooth muscle cells. Renal tubules-proximal, thick ascending limb of Henle and cortical collecting duct-are the site of the diversity of the K+ channel. ATP-sensitive K+ channel has been observed in the apical membranes of the thick ascending limb of Henle and collecting duct, and basolateral membrane of the proximal tubule. It was also shown that K+ channel opener increased renal hemodynamics and elicited diuretic and natriuretic effects. METHODS: To clarify the renal effects of WAY120491, a K+ channel opener, experiments were performed in unanesthetized normotensive and renal hypertensive rabbits allowing unilateral renal arterial infusion of agent. RESULTS: Intrarenal arterial infusion (0.13, 0.32 and 0.64 microgram/kg/min) of WAY120491 increaased CPAH, CCr, urine volume, UNaV, UKV and CH2O. Renal hemodynamic effects and increments of urine volume and free water clearance were completely blocked by glibenclamide (8.2 g/kg/min), while increments of UNaV and FENa were not significantly affected. Renal hemodynamic and tubular effects of WAY120491 were not significantly different in two-kidney one clip Goldblatt hypertensive rabbits from sham-operated rabbits. CONCLUSIONS: These results suggest that WAY120491 elicits renal effects through ATP-sensitive K+ channel in the renal vasculatures and renal tubules and the renal effects of WAT120491 may not be altered in the hypertension.

Effects of Fluoxetine on Membrane Potential and Ionic Currents in RINm5F Insulinoma Cells / 대한정신약물학회지

OBJECTIVE: The purpose of this study was to investigate the effects of fluoxetine (Prozac) on membrane potential and ionic currents in RINm5F insulinoma cells. METHODS: Membrane potential and ionic currents in RINm5F cell were recorded by using whole-cell and perforated-patch clamp techniques. RESULTS: Under current clamp conditions, diazoxide (200 microM), an activator of K ATP channels, induced a hyperpolarization of the resting membrane potential (-16.1+/-1.4 mV, n=), which was accompanied by a abolition of action potential firing. This diazoxide-induced hyperpolarization was blocked by glibenclamide (10 microM). Fluoxetine produced significant depolarization of membrane potential (15.9+/-3.1 mV, n=) and blocked diazoxide-induced hyperpolarization. Diazoxide activated inward currents in the presence of high external K + (90 mM) at a holding potential of -60 mV. Fluoxetine suppressed diazoxide-activated currents in a concentration-dependent (IC 50 =.84 microM) manner. However, the inhibitory action of fluoxetine was not specific to K ATP currents because it also inhibited both voltage-activated K + and Ca 2+ currents in a concentration-dependent manner. K ATP currents were more sensitive to fluoxetine block than both voltage-activated K + and Ca 2+ currents. CONCLUSION: Our results indicate that fluoxetine increased excitability of RINm5F cells mainly by the preferential block of K ATP currents. Fluoxetine-induced depolarization may influence insulin secretion in insulinoma cells.

Protective effects as ischemic preconditioning of sasanquasaponin mediated by K_(ATP) channel in the intact rat hearts 1 / 中国临床药理学与治疗学

AIM: To study protective effects as myocardial ischemic preconditioning of sasanquasaponin (SQS) and its relationship with K ATP channel. METHODS: The study adopted the model of myocardial ischemic injury induced by subcutaneous injection of isoproterenol (ISO) in rats, administering specific K ATP channel blocker gliberclamide (GLI 5 mg?kg -1 ). Four groups were set as NS group, I/R group, SQS group ( 0.2 mg?kg -1 ), and GLI group (5 mg?kg -1 ). Prior to injection of ISO, all agents were intraveneously injected into rats for 3 days, one time per day. Subsequently, ISO was subcutaneuously injected into rats by the ways of many different sites, and some indices were measured including ECG, serum creatine kinase (CK) activity, free fatty acid (FFA), and adenosine contents in rats. RESULTS: Preconditioningly intravenous injection of SQS could effectively protect myocardium from ischemic injury induced by ISO. With GLI injected prior to SQS, the cardioprotective effects of SQS were significantly attenuated. CONCLUSION: SQS can protect myocardium from ischemic injury induced by ISO, and the protection may be mediated by K ATP channel.

Effects of Cl- channel blockers on the cardiac ATP-sensitive K+ channel

To explore whether Cl- channel blockers interact with the ATP-sensitive K+ (KATP) channel, I have examined the effect of two common Cl- channel blockers on the KATP channel activity in isolated rat ventricular myocytes using patch clamp techniques. In inside-out patches, 4,4'-diisothio-cyanatostilbene-2,2'-disulfonic acid (DIDS) and niflumic acid applied to bath solution inhibited the KATP channel activity in a concentration-dependent manner with IC50 of 0.24 and 927 muM, respectively. The inhibitory action of DIDS was irreversible whereas that of niflumic acid was reversible. Furthermore, DIDS-induced block was not recovered despite exposure to ATP (1 mM). In cell-attached and inside-out patches, DIDS blocked the pinacidil- or 2,4-dinitrophenol (DNP)-induced KATP channel openings. In contrast, niflumic acid did not block the pinacidil-induced KATP channel openings in inside-out patches, but inhibited it in cell-attached patches. DIDS and niflumic acid produced additional block in the presence of ATP and did not affect current-voltage relationship and channel kinetics. All these results indicate that DIDS among Cl- channel blockers specifically blocks the cardiac KATP channel.

Mechanisms of relaxation of coronary artery by hypoxia

This study was designed to clarify the dependency of hypoxic coronary vasodilation (HCD) on the endothelium and the role of the K+ channels on HCD in the rabbit coronary artery. HCD was investigated in an isolated left circumflex coronary artery precontracted with prostaglandin F2 alpha. Vascular rings were suspended for isometric tension recording in an organ chamber filled with Krebs-Henseleit (KH) solution. Hypoxia was induced by gassing the chamber with 95% N2 + 5% CO2 and was maintained for 15 approximately 25 min. Hypoxia elicited a vasodilation in the precontracted coronary artery with and without endothelium. There was no difference between the amplitude of the HCD induced by two consecutive hypoxic challenges and the effects of 20% O2 + 5% CO2 + 75% N2 and 95% O2 + 5% CO2 control K-H solution of subsequent responses to hypoxia. Inhibition of the cyclooxygenase pathway by treatment with indomethacin had no effect on HCD. Blockades of the tetraethylammonium chloride-sensitive K+ channel abolished HCD. Apamin, a blocker of the small conductance Ca(2+)-activated K+ (KCa) channel, and iberiotoxin, a blocker of the large conductance KCa channel had no effect on HCD, respectively. Glibenclamide, a blocker of the ATP-sensitive K+ (K+ATP) channel, reduced HCD. Cromakalim, an opener of the K+ATP channel, relaxed the coronary artery precontracted with prostaglandin F2 alpha. The degree of relaxation by cromakalim was similar to that by hypoxia while glibenclamide reduced both hypoxia- and cromakalim-induced vasodilatations. In conclusion, these results suggest that HCD is independent on endothelium and HCD is considered to be induced by activation of K+ATP channel.

Imidazoline binding sites and receptors related with cardiovascular functions / 中国药理学通报

I 2 Imidazoline binding sites have been shown to exist on cardiac myocytes of human beings and rat. Both of I 1 and I 2 imidazoline binding sites have been identified on vascular smooth muscle cells of various species. Vascular I 2 imidazoline binding sites may participate in vascular smooth muscle proliferation. The sympathetic nerves supplying the cardiovascular system are endowed with presynaptic inhibitory imidazoline receptors. Being different from most of the imidazolines, moxonidine does not activate presynaptic imidazoline receptors, but SR141716A, which is considered as a selective antagonist at cannabinoid receptors, antagonizes presynaptic imidazoline receptors. It has been shown that imidazolines exhibit antiarrhythmic action. Agamatine, which is endogenous ligand at imidazoline receptors, not only decreases the rate of pacemaker firing in sinoatrial node of animal, prolongs action potential duration on cardiac myocytes of human beings and animal, but also inhibits afterdepolarizations induced by isoproterenol. On the other hand, imidazolines and guanidines inhibit the cardiovascular K ATP channel in a noncompetitive manner, those effects might interfere with the cardioprotective effects of K ATP channel.

Mechanisms of action of protein kinase C in myocardial preconditioning / 中国药理学通报

PKC plays a pivotal role in the mechanism of myocardial preconditioning. After preconditioning, PKC is activated and translocated to membranes and cytoskeleton structures by multiple endogenous substances such as adenosine, calcium, etc. Recent studies imply that MAPK carries the signal from PKC to the mitochondria K ATP channel and thus protect the heart.

Effect of hydrogen sulfide on rat cardiac function in vitro / 中国病理生理杂志

AIM: To observe the effect of hydrogen sulfide (H_2S) on the rat cardiac function in vitro, to explorer the physiological regulation of endogenous H_2S on myocardial action. METHODS: H_2S concentration and production in the rat myocardial tissues were detected. The expression of CSE (a kind of key enzyme of endogenous H_2S production) mRNA in myocardial tissues was screened by RT-PCR. Langendorff apparatus was used to perfuse the rat heart in vitro. After 20 minutes of stabilization, NaHS (10~-6 -10~-3 mol/L) were added cumulatively in order to the perfusive fluid, and another group applied physiological concentration NaHS (4?10~-4 mol/L), continuously perfusion for 20 min, heart rate (HR), difference of left ventricular pressure (△LVP), left ventricular peak rate of contraction (+LV dp/dt_~max ), peak rate of relaxation (-LV dp/dt_~max ) and coronary perfusive flow (CPF) were measured at the times. Finally, glibenclamide was applied to block the K_~ATP channel of heart, to observe the effect of NaHS at physiological concentration on cardiac function. RESULTS: NaHS concentration-dependently inhibited left ventricular ?dp/dt_~max and △LVP (P

Comparison of the effects of glimepiride and glibenclamide on neuropeptide Y secretion from hypothalamus in diabetic KK-Ay mice / 中华内分泌代谢杂志

Diabetic KK-Ay mice were given glimepiride (GM) and glibenclamide (GB). After treatment, the visceral white fat content, insulin and hypothalamic neuropeptide Y (NPY) levels were significantly lower in GM group than those in GB group, suggesting that in addition to the lower insulin level stimulated by GM, the lower concentration of hypothalamic NPY seems to play a role in lessening increase in body fat of type 2 diabetic animals treated with GM.