Identification of Muscarinic Receptors in Rat Cerebral Cortical Microvessels

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Abstract
Microvessels isolated from rat cerebral cortex consist mainly of capillaries (> 85%). Fresh, intact microvessel preparations were analyzed by radioligand binding techniques for muscarinic receptors. Scatchard analysis of specific quinuclidinyl benzilate(QNB) binding indicates that microvessels possess a large number of muscarinic sites (914 fmol/mg protein) of high affinity (Kd = 0.034 nM). The association and dissociation rate constants (0.37 min-1 nM-1 and 0.0067 min-1, respectively) yield an equilibrium Kd of 0.018 nM. Displacement of [3H]QNB by muscarinic ligands and control substances is typical of muscarinic receptors. The results indicate that cerebral microvessels possess a large population of muscarinic receptors.