Drugs online research references
J Pharmacol Exp Ther. 1991 Jan;256(1):222-9.
Chiral recognition of pinacidil and its 3-pyridyl isomer by canine cardiac and smooth muscle: antagonism by sulfonylureas.
Steinberg MI, Wiest SA, Zimmerman KM, Ertel PJ, Bemis KG, Robertson DW.
Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana.
Pinacidil, a potassium channel opener (PCO), relaxes vascular smooth muscle by increasing potassium ion membrane conductance, thereby causing membrane hyperpolarization. PCOs also act on cardiac muscle to decrease action potential duration (APD) selectively. To examine the enantiomeric selectivity of pinacidil, the stereoisomers of pinacidil (a 4-pyridylcyanoguanidine) and its 3-pyridyl isomer (LY222675) were synthesized and studied in canine Purkinje fibers and cephalic veins. The (-)-enantiomers of both pinacidil and LY222675 were more potent in relaxing phenylephrine-contracted cephalic veins and decreasing APD than were their corresponding (+)-enantiomers. The EC50 values for (-)-pinacidil and (-)-LY222675 in relaxing cephalic veins were 0.44 and 0.09 microM, respectively. In decreasing APD, the EC50 values were 3.2 microM for (-)-pinacidil and 0.43 microM for (-)-LY222675. The eudismic ratio was greater for the 3-pyridyl isomer than for pinacidil in both cardiac (71 vs. 22) and vascular (53 vs. 17) tissues. (-)-LY222675 and (-)-pinacidil (0.1-30 microM) also increased 86Rb efflux from cephalic veins to a greater extent than did their respective optical antipodes. The antidiabetic sulfonylurea, glyburide (1-30 microM), shifted the vascular concentration-response curve of (-)-pinacidil to the right by a similar extent at each inhibitor concentration. Glipizide also antagonized the response to (-)-pinacidil, but was about 1/10 as potent with a maximal shift occurring at 10 and 30 microM. Glyburide antagonized the vascular relaxant effects of 0.3 microM (-)-LY222675 (EC50, 2.3 microM) and reversed the decrease in APD caused by 3 microM (-)-LY222675 (EC50, 1.9 microM). Nitroprusside did not alter 86Rb efflux, and vascular relaxation induced by sodium nitroprusside was unaffected by sulfonylureas. Thus, the enantiomers of the 3-pyridyl isomer of pinacidil demonstrate enhanced stereospecificity in both canine cardiac and vascular tissues compared to the enantiomers of pinacidil. However, the relative selectivity of pinacidil and its 3-pyridyl isomer for cardiac and vascular smooth muscle remains unaltered. Sulfonylureas antagonize the more potent enantiomers in both tissues, supporting the involvement of an ATP-sensitive potassium channel in the action of PCOs; however, antagonism in canine vascular smooth muscle by sulfonylureas does not resemble classical competitive antagonism.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1899116&dopt=Abstract
J Pharmacol Exp Ther. 1991 Feb;256(2):480-5.
RP 49356 and cromakalim relax airway smooth muscle in vitro by opening a sulphonylurea-sensitive K+ channel: a comparison with nifedipine.
Raeburn D, Brown TJ.
Rhone-Poulenc Rorer Inc., Dagenham Research Center, Essex, England.
RP 49356 is a novel compound which relaxes airway smooth muscle in vitro. Like cromakalim, RP 49356 reduced contractility in guinea pig isolated trachealis under basal conditions or when challenged with low (less than 20 mM) but not high K+. These effects were antagonized by the sulphonylureas glibenclamide and glipizide. This spectrum of action is typical of the class of compounds known as potassium channel openers (KCOs). Unlike RP 49356 and cromakalim, nifedipine had no effect on basal tone, relaxed tissues contracted with low or high K+ and was not antagonized by the sulphonylureas. These data suggest that the KCOs are not acting directly at the voltage-gated Ca++ channel in this tissue. RP 49356 and cromakalim were similar to nifedipine by being more potent at relaxing tissues precontracted with carbachol or histamine (spasmolytic effects) than they were at preventing initiation of the response to these spasmogens (antispasmogenic effects). Because the maintained phase of contraction in airway smooth muscle may be associated with some Ca++ influx, the data presented here suggests that, like nifedipine, the KCOs are more active smooth muscle relaxants under conditions of Ca++ influx. In summary, RP 49356, like cromakalim, is a compound which relaxes airway smooth muscle in vitro by opening a sulphonylurea-sensitive K+ channel which may be similar to the ATP-sensitive K+ channel found in other tissues.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1899701&dopt=Abstract
J Pharmacol Exp Ther. 1991 May;257(2):901-7.
Quantitative autoradiography of the binding sites for [125I] iodoglyburide, a novel high-affinity ligand for ATP-sensitive potassium channels in rat brain.
Gehlert DR, Gackenheimer SL, Mais DE, Robertson DW.
Central Nervous System Research, Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana.
We have developed a high specific activity ligand for localization of ATP-sensitive potassium channels in the brain. When brain sections were incubated with [125I]iodoglyburide (N-[2-[[[(cyclohexylamino)carbonyl]amino]sulfonyl]ethyl]-5-125I-2- methoxybenzamide), the ligand bound to a single site with a KD of 495 pM and a maximum binding site density of 176 fmol/mg of tissue. Glyburide was the most potent inhibitor of specific [125I]iodoglyburide binding to rat forebrain sections whereas iodoglyburide and glipizide were slightly less potent. The binding was also sensitive to ATP which completely inhibited binding at concentrations of 10 mM. Autoradiographic localization of [125I]iodoglyburide binding indicated a broad distribution of the ATP-sensitive potassium channel in the brain. The highest levels of binding were seen in the globus pallidus and ventral pallidum followed by the septohippocampal nucleus, anterior pituitary, the CA2 and CA3 region of the hippocampus, ventral pallidum, the molecular layer of the cerebellum and substantia nigra zona reticulata. The hilus and dorsal subiculum of the hippocampus, molecular layer of the dentate gyrus, cerebral cortex, lateral olfactory tract nucleus, olfactory tubercle and the zona incerta contained relatively high levels of binding. A lower level of binding (approximately 3- to 4-fold) was found throughout the remainder of the brain. These results indicate that the ATP-sensitive potassium channel has a broad presence in the rat brain and that a few select brain regions are enriched in this subtype of neuronal potassium channels.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1903447&dopt=Abstract
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