Effect of arginine vasotocin on plasma concentration and water tissues in terrestrial toad Bufo viridis and semi-aquatic frog Rana ridibunda

Muscarinic acetylcholine receptors in invertebrates: comparisons with homologous receptors from vertebrates

The pharmacology, physiology and molecular biology of invertebrate muscarinic acetylcholine receptors are compared with current knowledge concerning vertebrate muscarinic acetylcholine receptors. Evidence for the existence of multiple receptor subtypes in invertebrates is examined, emphasizing what is presently known about the sensitivity of invertebrate preparations to subtype selective ligands previously defined in vertebrate studies. Other evidence for muscarinic receptor subtypes which is examined includes: heterogeneous responses to classical muscarinic ligands and evidence for coupling of invertebrate muscarinic receptors to several different classes of second messenger systems. Clues regarding possible functions for invertebrate muscarinic receptors are discussed, including evidence from both physiological studies and in situ localization studies which reveal patterns of receptor protein and mRNA expression. A detailed analysis of the structural similarities between a cloned Drosophila muscarinic receptor and vertebrate muscarinic receptors is also presented. Regions of the receptors that may be involved in ligand binding, effector coupling and receptor regulation are identified in this comparison. Future directions for invertebrate muscarinic receptor research are considered including: methods for cloning other receptor subtypes, methods for cloning homologous receptors from other species and genetic approaches for determining the physiological roles of muscarinic receptors.

Characterization of muscarinic cholinergic receptors in the crab nervous system

The selective muscarinic antagonist L-[3H]-quinuclidinyl benzilate (L-[3H]QNB) binds reversibly and with high affinity (KD = 0.3 nM) to a single population (Bmax = 105 fmol/mg protein) of specific sites in nervous tissue of the crab Cancer magister. The binding site is stereoselective; (-)QNB is over 200 times more potent than (+)QNB as an inhibitor of specific L-[3H]QNB binding. The muscarinic antagonists scopolamine and atropine are over 10,000 times more potent inhibitors of L-[3H]QNB binding than the nicotinic antagonists decamethonium and d-tubocurarine. The muscarinic agonists oxotremorine, pilocarpine, arecoline, and carbachol also compete effectively for the L-[3H]QNB binding site. This pharmacological profile strongly suggests the presence of classical muscarinic receptors in the crab nervous system. These receptors are localized to nervous tissue containing cell bodies and neuropil, whereas specific L-[3H]QNB binding is low or absent in peripheral nerve, skeletal muscle, and artery.