3H-clonidine and 3H-yohimbine binding to glass fiber filters: implications for studies with platelet membranes.

3H-Clonidine and 3H-yohimbine were observed to bind to glass fiber filters. The binding was displaced by co-filtration with the corresponding non-radioactive ligand. Phentolamine and (--)-norepinephrine were ineffective in displacing either 3H-clonidine or 3H-yohimbine bound to filters. Failure to correct for filter binding resulted in an over-estimation of specific binding to platelet membranes. Certain published methodologies may have consequently misidentified up to 20% of the specific binding to platelets, that was actually due to displaced filter binding. Experimental conditions are described which eliminate filter binding. These results are significant for the interpretation of data from studies of platelet binding in depressed patients.