Muscarinic receptors on rat ileal villus and crypt cells

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Abstract
Ileal villus and crypt cells exhibit morphological and biochemical differences which may be responsible for functional differences in relation to ion transport. Cholinergic agonists act directly on epithelial cell muscarinic receptors, but it is not known if these receptors exist on both villus and crypt cells. Using the potent muscarinic antagonist [3H](−)-quinuclidinyl benzilate (QNB) we have determined the distribution of muscarinic receptors in rat ileal villus and crypt cells. Plasma membrane preparations from ileal villus and crypt cells possessed a specific, saturable, and high affinity QNB binding site with apparent dissociation constants of 0.23 ± 0.05 and 0.21 ± 0.04 nM (mean ± s.e., n = 6) and densities of 92.2 ± 2.8 and 90.1 ± 16.2 fmol (mg protein)−1, respectively. Both types of cells showed similar potencies for agonist and antagonist competition of QNB binding. The muscarinic receptors in membrane fractions from villus cells were found primarily on the basolateral membrane rather than on the brush border membrane. Secretion induced by cholinergic stimulation of the small intestine might, therefore, be due to an effect on both villus and crypt cells as both types contain muscarinic receptors. Furthermore, such stimulation also may result in mucin secretion, as goblet cells were present in the preparation we studied, and receptors on these cells may have contributed to the amount of binding of [3H]QNB.