Binding of [3H]atropine by cardiac plasma membrane-enriched fractions

The binding of [3H]atropine by the primary subcellular fractions and plasma membrane-enriched fractions from atria and ventricles of various species was measured by the Millipore filtration technique. Although all of the primary particulate fractions exhibited binding activities, the bulk of the total homogenate binding activity was associated with the washed particles sedimenting at the lower gravitational forces; this was observed with either atria or ventricles of dog, guinea pig, rabbit, hamster, and rat. Plasma membrane-enriched fractions isolated from the right atrium of guinea pig exhibited atropine binding activities with characteristics similar to dog atrial membranes; binding activity was moderately enriched in these membranes with respect to the starting material.