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Clamp Method (clamp + method)
Selected AbstractsPharmacodynamics of Insulin Detemir and Insulin Glargine Assessed by an Isoglycemic Clamp Method in Healthy CatsJOURNAL OF VETERINARY INTERNAL MEDICINE, Issue 4 2010C. Gilor Background: Insulin detemir and insulin glargine are synthetic long-acting insulin analogs. In people, insulin glargine is longer acting and has a relatively flat time-action profile, while insulin detemir has significantly less within-subject variability. Insulin detemir is also associated with less undesired weight gain and decreased frequency of hypoglycemic events. Objectives: To compare the pharmacodynamics of insulin detemir and insulin glargine in healthy cats. Animals: Ten young, healthy, neutered, purpose-bred cats. Methods: Randomized, cross-over design. Pharmacodynamics of insulin detemir and insulin glargine were determined by the isoglycemic clamp method after a 0.5 U/kg SC injection. Results: The only significant difference in the pharmacodynamics of insulin detemir and insulin glargine was onset of action (1.8 ± 0.8 and 1.3 ± 0.5 hours for insulin detemir and insulin glargine, respectively, P= .03). End of action of insulin detemir was reached at 13.5 ± 3.5 hours and for insulin glargine at 11.3 ± 4.5 hours (P= .18). Time-to-peak action of insulin detemir was reached at 6.9 ± 3.1 hours and for insulin glargine at 5.3 ± 3.8 hours (P= .7). The time-action curves of both insulin analogs varied between relatively flat curves in some cats and peaked curves in others. Conclusion and Clinical Importance: Insulin detemir and insulin glargine have shorter durations of action than in people when assessed by the clamp method, but in some cats these insulin analogs could be useful as once-a-day drugs. Peak effects of both insulin analogs are pronounced in some cats. [source] Ionic Basis for Action Potential Prolongation by Phenylephrine in Canine Epicardial MyocytesJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 1 2000RICHARD B. ROBINSON Ph.D. Phenylephrine Action on Repolarization. Introduction: In canine ventricle, ,-adrenergic agonists prolong action potential duration (APD) without any effect on the action potential notch, suggesting that, in this species, the effect on repolarization might he independent of inhibition of Ito. The present study investigated the action of the ,-adrenergic agonist phenylephrine on the action potential and the repolarizing currents Ito and IK in isolated canine epicardial myocytes. Methods and Results: Isolated cells from canine epicardial tissue, and Purkinje fibers, were studied with the whole cell, voltage clamp method. Phenylephrine 0.1 ,M increased APD by 13%± 4% at 90% repolarization without affecting the notch or amplitude. Under voltage clamp, concentrations of phenylephrine as high as 10 ,M had no effect on Itp in canine epicardial myocytes. However, Ito of isolated canine Purkinje myocytes was reduced to 69%± 7% of control by 1 ,M phenylephrine. Further studies in canine epicardial myocytes revealed an action of phenylephrine to inhibit Ik, and in particular IKs Using a voltage protocol that included a two-step repolarization to separate IKs and IKr tail components, the largely 1Ke, component was not significantly affected by 1 ,M phenylephrine, whereas the largely IKs component was reduced to 81%± 5% of control value. Conclusion: ,-Adrenergic prolongation of repolarization in canine epicardium does not result from inhibition of Ito. Rather, it appears that reduction of IKs contributes to the action of phenylephrine. The unresponsiveness of epicardial Ito is not a general characteristic of the canine heart, because Purkinje myocyte Ito was inhibited, suggesting regional differences in the molecular basis of lto, and/or a-adrenergic signaling in the canine heart. [source] Inhibitory effect of erythromycin on potassium currents in rat ventricular myocytes in comparison with disopyramideJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 7 2003Erika Hanada ABSTRACT Disopyramide, a class la antiarrhythmic agent, has been reported to induce torsades de pointes (TdP) associated with excessive QT prolongation in electrocardiogram (ECG), especially when concomitantly administered with erythromycin, a macrolide antibiotic agent. In this study, we have evaluated the effects of erythromycin on action potential duration (APD) and potassium currents in rat ventricular myocytes in comparison with disopyramide. We have evaluated the relationship between in-vitro potassium current inhibition and in-vivo QT prolongation observed in a previous study. Action potentials and membrane potassium currents, including delayed rectifier current (IK) and transient outward current (Ito), were recorded using a whole-cell patch clamp method in enzymatically-dissociated ventricular cells. Erythromycin and disopyramide prolonged APD in a concentration-dependent manner. Disopyramide (10,100 ,m) and erythromycin (100 ,m) led to increases in the APD at 90% repolarization level. Disopyramide reduced IK (IC50 = 37.2 + 0.17 ,m) and Ito (IC50 = 20.9 + 0.13 ,m) while erythromycin reduced IK (IC50 = 60.1 + 0.29 ,m) but not Ito. The observed prolongation of APD might be ascribed to the inhibition of potassium currents. Erythromycin produced the prolongation of APD and the inhibition of potassium currents with a lag time after addition of the drugs, which suggested that erythromycin might not reach potassium channels from outside the ventricular cells. The potency of disopyramide was almost equivalent under in-vitro and in-vivo conditions. However, potency of erythromycin in-vitro was far weaker than that in-vivo reported in a previous study, presumably due to a difference in the uptake of erythromycin into ventricular myocytes between in-vivo and in-vitro conditions. Therefore, when drug-induced risks of QT prolongation are to be evaluated, the difference of potencies between in-vitro and in-vivo should be taken into consideration. [source] In Vivo Time-Course Changes in Ethanol Levels Sampled With Subcutaneous MicrodialysisALCOHOLISM, Issue 3 2008Eric A. Engleman Background:, The objective of this study was to determine time-course changes in in vivo ethanol (EtOH) concentrations using a novel subcutaneous (s.c.) microdialysis sampling technique. The hypothesis to be tested was that EtOH concentrations in the s.c. fluid would reflect blood EtOH concentrations. If this is the case, then s.c. microdialysis could allow a more detailed analysis of changes in in vivo levels of EtOH under different drinking paradigms. Methods:, Adult male and female Wistar rats and male alcohol-preferring (P) rats were used in this study. A loop-style microdialysis probe was designed for s.c. applications. After initial in vitro characterization, probes were implanted under the skin between the shoulder blades. Animals were allowed to recover 4 to 24 hours prior to microdialysis collection (2.0 ,l/min flow rate with isotonic saline). In vivo microdialysis experiments were then conducted to determine (i) the extraction fraction (or clearance) using EtOH no-net-flux (NNF) coupled with the alcohol clamp method, (ii) the dose,response and time-course effects after systemic EtOH administration and to compare with blood EtOH levels, and (iii) the time-course changes in EtOH levels during and after an EtOH drinking episode. Results:, In vivo probe recovery (extraction fraction) obtained using the alcohol clamp method was 69 ± 3%, and was comparable to the in vitro recovery of 73 ± 2%. For the EtOH dose,response experiment, rats injected i.p. with 0.5, 1.0, or 2.0 g/kg EtOH showed a clear dose,response effect in the s.c. dialysate samples. Peak concentrations (70, 123, and 203 mg%, respectively) were reached by 15 minutes after injection. In an experiment comparing levels of EtOH in s.c. dialysis and arterial blood samples in rats administered 1.0 g/kg EtOH, similar time-course changes in in vivo EtOH concentrations were observed with both i.g. and i.p. EtOH administration. In P rats drinking 15% EtOH during a 1-hour scheduled access period, EtOH levels in s.c. microdialysates rose rapidly over the session and peaked at approximately 50 mg% at 60 to 80 minutes. Conclusions:, Overall, these experiments indicate that s.c. EtOH and blood EtOH concentrations follow a similar time course. Moreover, s.c. microdialysis can be useful as an experimental approach for determining detailed time-course changes in in vivo EtOH concentrations associated with alcohol drinking episodes. [source] Pharmacodynamics of Insulin Detemir and Insulin Glargine Assessed by an Isoglycemic Clamp Method in Healthy CatsJOURNAL OF VETERINARY INTERNAL MEDICINE, Issue 4 2010C. Gilor Background: Insulin detemir and insulin glargine are synthetic long-acting insulin analogs. In people, insulin glargine is longer acting and has a relatively flat time-action profile, while insulin detemir has significantly less within-subject variability. Insulin detemir is also associated with less undesired weight gain and decreased frequency of hypoglycemic events. Objectives: To compare the pharmacodynamics of insulin detemir and insulin glargine in healthy cats. Animals: Ten young, healthy, neutered, purpose-bred cats. Methods: Randomized, cross-over design. Pharmacodynamics of insulin detemir and insulin glargine were determined by the isoglycemic clamp method after a 0.5 U/kg SC injection. Results: The only significant difference in the pharmacodynamics of insulin detemir and insulin glargine was onset of action (1.8 ± 0.8 and 1.3 ± 0.5 hours for insulin detemir and insulin glargine, respectively, P= .03). End of action of insulin detemir was reached at 13.5 ± 3.5 hours and for insulin glargine at 11.3 ± 4.5 hours (P= .18). Time-to-peak action of insulin detemir was reached at 6.9 ± 3.1 hours and for insulin glargine at 5.3 ± 3.8 hours (P= .7). The time-action curves of both insulin analogs varied between relatively flat curves in some cats and peaked curves in others. Conclusion and Clinical Importance: Insulin detemir and insulin glargine have shorter durations of action than in people when assessed by the clamp method, but in some cats these insulin analogs could be useful as once-a-day drugs. Peak effects of both insulin analogs are pronounced in some cats. [source] Diabetes attenuates the minimum anaesthetic concentration (MAC) and MAC-blocking adrenergic response reducing actions of clonidine in ratsACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 10 2001T. Kita Background: It is well known that clonidine, an ,2 agonist, reduces anaesthetic requirement and attenuates haemodynamic responses against noxious stimuli. However, the diabetic state is known to affect several functions of ,2 adrenoceptors. We investigated the effects of streptozotocin (STZ)-induced diabetes mellitus (DM) on these beneficial actions of clonidine in halothane-anaesthetized rats. Methods: The rats were randomly assigned to one of three groups: diabetes (n=24, induced by 50 mg · kg,1 IV STZ), diabetes treated with insulin (n=24), or control (n=24). We evaluated the effects of clonidine on minimum anaesthetic concentration (MAC) and minimum concentration of halothane needed to suppress cardiovascular responses evoked by a noxious stimulus (MAC-blocking adrenergic responses: MAC-BAR) in each group. MAC and MAC-BAR of halothane were determined by the tail clamp method. MAC-BAR was defined as the MAC which attenuated haemodynamic responses within 10% following the tail clamp. Results: The diabetic state decreased MAC of halothane by approximately 10%, while MAC-BAR of halothane had been little affected. In the diabetes group, MAC reducing action of clonidine (30 and 100 ,g · kg,1, IV) was completely abolished and MAC-BAR reducing action of clonidine was partially reduced (30 but not 100 ,g · kg,1, IV). Insulin treatment preserved these actions of clonidine. Conclusion: It is suggested that the diabetic state attenuates the beneficial actions of clonidine and that insulin treatment of diabetes preserves these actions of clonidine. [source] Emodin Inhibits Voltage-Dependent Potassium Current in Guinea Pig Gallbladder Smooth MuscleBASIC AND CLINICAL PHARMACOLOGY & TOXICOLOGY, Issue 3 2009Zhi-Xuan Wu We studied the effects of emodin on the contraction of gallbladder smooth muscle and voltage-dependent K+ current in gallbladder smooth muscle cells. Gallbladder muscle strips were obtained from adult guinea pigs and the resting tension was recorded. Gallbladder smooth muscle cells were isolated by enzymatic digestion, and K+ current was recorded by the whole-cell patch clamp method. Emodin increased the resting tension of gallbladder smooth muscle strips and inhibited voltage-dependent K+ current in a dose-dependent manner. When 10 µM emodin was applied to gallbladder smooth muscle cells for 3,6 min., the amplitude of voltage-dependent K+ current was decreased by 31.5 ± 0.5% at +40 mV, and this inhibitory effect mostly recovered after washout. The steady-state inactivation curves were shifted in a hyperpolarizing direction by emodin. In the presence of the protein kinase C inhibitors staurosporine and chelerythrine, the effect of emodin on voltage-dependent K+ current was significantly attenuated. In conclusion, emodin promotes gallbladder contraction, mainly by inhibiting voltage-dependent K+ current via the protein kinase C pathway. These findings provide theoretical foundation for the application of emodin in gallbladder motility disorders. [source] Clinical significance of pretreatment serum amphiregulin and transforming growth factor-,, and an epidermal growth factor receptor somatic mutation in patients with advanced non-squamous, non-small cell lung cancerCANCER SCIENCE, Issue 11 2008Katsuhiro Masago Circulating amphiregulin and transforming growth factor-, (TGF-,) have been found to be correlated with an unfavorable response to gefitinib based on the identification of patients with a higher probability of resistance to the drug. However, the association between an epidermal growth factor receptor (EGFR) somatic mutation and the overexpression of its ligands has not been determined. To verify the clinical significance of the two serum markers and EGFR mutation status, we determined serum amphiregulin and TGF-, levels by enzyme-linked immunosorbent assay in 93 patients with advanced non-squamous, non-small cell lung cancer and EGFR somatic mutation status using the peptic nucleic acid-locked nucleic acid clamp method in 46 cases. The relationship between each independent clinicopathological variable and the response to gefitinib therapy was examined. We also evaluated the risk factors associated with prognosis. Fourteen (41.0%) of 34 progressive disease cases were positive for amphiregulin (P = 0.007). Eleven (32.4%) of 34 progressive disease cases were positive for TGF-, (P = 0.005). The median survival time of patients with the EGFR somatic mutation was significantly longer (P = 0.01). The same was true of amphiregulin- (P = 0.046) and TGF-,-negative patients (P < 0.01). In multivariate analysis, serum TGF-, positivity (hazard ratio, 2.558; P = 0.005) and the wild type EGFR gene (hazard ratio, 1.894; P = 0.003) were significant independent prognostic factors. Our study demonstrates that the status of the serum EGFR ligand, in addition to EGFR activating mutation, is a predictive factor for response to gefitinib therapy. (Cancer Sci 2008; 99: 2295,2301) [source] Functional Studies of Synthetic Gramicidin Hybrid Ion Channels in CHO CellsCHEMBIOCHEM, Issue 5 2007Ryszard Wesolowski Abstract The function of a gramicidin hybrid ion channel in living Chinese hamster ovary (CHO) cells was investigated by the patch clamp method. The synthetic ion channel 1 consists of two cyclohexyl ether amino acids that link two minigramicidin strands. With 1 at a concentration of 1.0 ,M, an increase in the whole-cell membrane conductance was observed after 1.37 min. The conductance showed larger currents when Cs+ was used as charge carrier than when Na+ and K+ were used. In single-channel recordings with Cs+ as charge carrier, the substance showed comparable single-channel amplitudes in the membrane of living cells and artificial black lipid bilayers. In addition to functioning as a cation channel, compound 1 appeared to be a water channel. Exposure of the CHO cells to an extracellular hypoosmotic solution did not substantially change the cell volume. Extracellular hypoosmotic conditions in the presence of 1 increased the cell size to 146.5,% that of the control. Thus, the synthetic hybrid channel 1 can function as a cation channel with some Cs+ specificity, and as a water channel in CHO cells. [source] | ||||||||||