The Muscarinic Receptor Subtype on Gastric Isolated Smooth Muscle Cells
A recently proposed classification of muscarinic receptor subtypes in based on the regional differences in the affinities of these receptors for selective antagonists and agonists (Hammer and Giachietti 1983). Estimates of muscarinic receptor affinity are usually obtained from direct radioligand binding studies performed on subcellular fractions and from the measurement of biological responses of intact tissues. The extent to which these data are comparable is questionable since different experimental conditions pertain to the two approaches. This is particularly important with respect to the muscarinic receptor, the characteristics of which may be influenced by factors such as local concentrations of guanine nucleotides (Wei and Sulakahe 1979; Berrie et al. 1979; Rosenberger et al. 1979; Harden et al. 1982), muscarinic agonists (Klein et al. 1979), cations (Aronstam et al. 1978) and the ionic strength of the incubation medium (Burgen and Spero 1970). As a result, assessment of the affinity derived from radioligand binding studies performed on subcellular fractions in low ionic strength media may not be comparable to those derived from the measurement of biological responses of whole tissues suspended in physiological buffers.
KeywordsMuscarinic Receptor Circular Muscle Muscarinic Agonist Muscarinic Antagonist Muscarinic Receptor Subtype
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