Muscarinic receptor binding in the mouse heart: the selective modulatory effect of fluoride ion on agonist binding

The effect of fluoride ion on the binding of the specific muscarinic agonist ligand [ 3H]c is methyldioxolane ([ 3H]CD) to the mouse cardiac muscarinic receptor was investigated. Utilizing equilibrium ligand binding experiments, sodium fluoride (10mM) was shown to decrease [ 3H]CD binding, measured at a concentration of 2 nM, by 52%. Studies with several different ions demonstrated that the reduction in [ 3H]CD binding was a specific effect of fluoride. This fluoride modulation was selective for agonist binding, as no effect of fluoride on the binding of the muscarinic antagonist [ 3H](−) quinuclidinyl benzilate (QNB) was observed.