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Interaction of agonists and selective antagonists with gastric smooth muscle muscarinic receptors (1989)

Lucchesi, P. A. ; Romano, F. D. ; Scheid, C. R. ; [et al.]

Springer

Naunyn-Schmiedeberg's archives of pharmacology 339 (1989), S. 145-151

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ISSN: 1432-1912

Keywords: Smooth muscle ; Muscarinic receptors ; G Proteins ; Selective antagonists

Source: Springer Online Journal Archives 1860-2000

Topics: Medicine

Notes: Summary The interaction of cholinergic agonists and antagonists with smooth muscle muscarinic receptors has been investigated by measurement of displacement of the muscarinic antagonist [3H]QNB (quinuclidinyl benzilate) in membranes prepared from toad stomach. The binding of [3H]QNB was saturable, reversible and of high affinity (K D = 423 pM). The muscarinic receptor subtypes present in gastric smooth muscle were classified by determining the relative affinities for the selective antagonists pirenzepine (M1), AF-DX 116 (M2) and 4-DAMP (M3). The results from these studies indicate the presence of a heterogeneous population of muscarinic receptor subtypes, with a majority (88%) exhibiting characteristics of M3 receptors and a much smaller population (12%) exhibiting characteristics of M2 receptors. The binding curve for the displacement of [3H]QNB binding by the agonist oxotremorine was complex and was consistent with presence of two affinity states: 24% of the receptors had a high affinity (K D = 4.7 nM) for oxotremorine and 76% displayed nearly a 1,000-fold lower affinity (K D = 4.4 μM). When oxotremorine displacement of [3H]QNB binding was determined in the presence GTPγS, high affinity binding was abolished, indicating that high affinity agonist binding may represent receptors coupled to G proteins. Moreover, pertussis toxin pretreatment of membranes also abolished high affinity agonist binding, indicating that the muscarinic receptors are coupled to pertussis toxin-sensitive G proteins. Reaction of smooth muscle membranes with pertussis toxin in the presence [32P]NAD caused the [32P]-labelling of a 40 kD protein that may represent the α subunit(s) of G proteins that are known to be NAD-ribosylated by the toxin. We conclude that both M3 and M2 receptors may be coupled to G proteins in a pertussis-sensitive manner.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00165136

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Effects of static magnetic fields on diffusion in solutions (1988)

Kinouchi, Y. ; Tanimoto, S. ; Ushita, T. ; [et al.]

New York, NY [u.a.] : Wiley-Blackwell

Bioelectromagnetics 9 (1988), S. 159-166

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ISSN: 0197-8462

Keywords: Lorentz force ; Maxwell stress ; threshold field strength ; Life and Medical Sciences ; Occupational Health and Environmental Toxicology

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Biology , Physics

Notes: Static magnetic fields affect the diffusion of biological particles in solutions through the Lorentz force and Maxwell stress. These effects were analyzed theoretically to estimate the threshold field strength for these effects. Our results show that the Lorentz force suppresses the diffusion of charged particles such as Na+, K+, Ca2+, Cl-, and plasma proteins. However, the threshold is so high, i.e., more than 104 T, that the Lorentz force does not affect the ion diffusion at typical field strengths (a few Tesla at most). Since the threshold of gradient fields for producing a change in ion diffusion through the Maxwell stress is more than 105 T2/m for paramagnetic molecules (FeCl3, O2) and plasma proteins, their diffusion would be unaffected by typical gradient fields (100 T2/m at most) and even by high gradient fields (less than 105 T2/m) used in magnetic separation techniques. In contrast, movement of deoxygenated erythrocytes and FeCl3 colloids (more than 103 molecules) is influenced by the usual gradient fields due to a volume effect.

Additional Material: 1 Ill.