Drugs online research references
lenti.med.umn.edu
Using the program Microsoft EXCEL, a spreadsheet was developed for constrained, simultaneous analysis of multiple datasets obtained from equilibrium binding experiments, according to an allosteric model of interaction. This approach was used to quantitate the interaction between the modulator (heptane-1,7-bis (dimethyl 3'-phthalimidopropyl) ammonium bromide) (C7/3-phth) and the radioligands [3H]N-methylscopolamine and [3H]quinuclidinyl benzilate at cortical and atrial muscarinic receptors. The interaction between various concentrations of the radioligands and C7/3-phth, in the guinea pig atrium and in the rat cerebral cortex, could be well described by the allosteric model. The affinity of C7/3-phth for unoccupied atrial receptors was significantly higher than for cortical receptors. The negative cooperativity between [3H]quinuclidinyl benzilate and the modulator was higher in cortex than that between the modulator and [3H]N-methylscopolamine. It is suggested that the described method has wide applicability because of the extensive availability of spreadsheet programs, the analytical advantages offered by constrained, simultaneous nonlinear regression and the ability to adapt the spreadsheet to almost any model of ligand-receptor interaction.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9754944&dopt=Abstract
Br J Pharmacol. 1998 Aug;124(8):1615-22.
Characterization of an atypical muscarinic cholinoceptor mediating contraction of the guinea-pig isolated uterus.
Boxall DK, Ford AP, Choppin A, Nahorski SR, Challiss RA, Eglen RM.
Department of Cell Physiology and Pharmacology, University of Leicester, USA.
In many smooth muscle tissues a minor M3-muscarinic acetylcholine (mACh) receptor population mediates contraction, despite the presence of a larger M2-mACh receptor population. However, this is not the case for guinea-pig uterus where radioligand binding and functional studies exclude a dominant role for M3-mACh receptors. Using tissue from animals pre-treated with diethylstilboestrol, estimates of antagonist affinity were made before and after selective alkylation procedures, together with estimates of agonist affinity to characterise the mACh receptor population mediating carbachol-induced contraction of guinea-pig isolated uterus. Antagonist affinity estimates made at 'protected' receptors were not significantly different from those made in untreated tissues. However all estimations were significantly different from those reported in guinea-pig ileum and atria. The rank order of affinities were atropine>zamifenacin=tripitramine> methoctramine. Carbachol-induced contractions were insensitive to the M4-selective muscarinic toxin MTx-3, or PD102807 (0.1 microM) ruling out a role for M4-mACh receptors. The agonist affinity value for L-660,863, a putative 'M2-selective' agonist of 5.44+/-0.30 (n=6) was significantly different from that reported in guinea-pig atria. In contrast, the pKA value for carbachol (4.22+/-0.17 n = 8) agrees with that reported for guinea-pig ileum. Carbachol-induced contractions were insensitive to pertussis toxin although carbachol-induced inhibition of forskolin-stimulated cyclic AMP production was attenuated, ruling out the involvement of Gi-proteins in contraction. Radioligand binding studies revealed a KD for N-[3H]-methylscopolamine of 0.12+/-0.05 nM and a Bmax of 147+/-18 fmol mg protein(-1). Antagonist affinity estimates made using competition binding studies supported previous data suggesting the presence of a homogenous population of M2-mACh receptors. These data suggest a small population of mACh receptors with an atypical operational profile which can not be distinguished using radioligand binding studies may mediate carbachol-induced contraction of guinea-pig isolated uterus.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9756376&dopt=Abstract
uniroma2.it
Cortical glutamatergic fibres and cholinergic inputs arising from large aspiny interneurons converge on striatal spiny neurons and play a major role in the control of motor activity. We have investigated the interaction between excitatory amino acids and acetylcholine (ACh) on striatal spiny neurons by utilizing intracellular recordings, both in current- and in voltage-clamp mode in rat brain slices. Muscarine (0.3-10 microM) produced a reversible and dose-dependent increase in the membrane depolarizations/inward currents induced by brief applications of N-methyl-D-aspartate (NMDA), while it did not affect the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)-induced responses. These concentrations of muscarine did not alter the membrane potential and the current-voltage relationship of the recorded cells. Neostigmine (0.3-10 microM), an ACh-esterase inhibitor, mimicked this facilitatory effect. The facilitatory effects of muscarine and neostigmine were antagonized either by scopolamine (3 microM) or by pirenzepine (10-100 nM), an antagonist of M1-like muscarinic receptors, but not by methoctramine (300 nM), an antagonist of M2-like muscarinic receptor. Accordingly, these facilitatory effects were mimicked by McN-A-343 (1-10 microM), an agonist of M1-like muscarinic receptors, but not by oxotremorine (300 nM), an agonist of M2-like receptors. Tetrodotoxin (TTX) did not block the facilitatory effect produced by the activation of muscarinic receptors suggesting that this effect is postsynaptically mediated. The action of neostigmine was prevented either by the intracellular calcium (Ca2+) chelator BAPTA (200 mM) or by preincubating the slices with inhibitors of protein kinase C (PKC) (staurosporine 100 nM or calphostin C 1 microM). McN-A-343 did not alter the excitatory post synaptic potentials (EPSPs) evoked by corticostriatal stimulation in the presence of physiological concentration of magnesium (Mg2+ 1.2 mM), while it enhanced the duration of these EPSPs recorded in the absence of external magnesium. Our data show that endogenous striatal ACh exerts a positive modulatory action on NMDA responses via M1-like muscarinic receptors and PKC activation.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9758158&dopt=Abstract
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