Ascorbate increases apparent "specific" binding of [3H]pyrilamine to glass fiber filters

Although filtration through glass fiber filters provides a convenient method for separating bound from unbound radioligand, binding of the ligand to the filters is often a problem. Ascorbate (0.1%) has been shown to decrease binding of serotonergic acids to these filters. In the present study, relatively high binding of [3H]pyrilamine, an H1-antagonist, to glass fiber filters was observed. The addition of ascorbate increased, rather than decreased, binding of [3H]pyrilamine to the filters. Thus, the effect of ascorbate on binding of radioligands to glass fiber filters appears to be dependent upon the particular ligand involved.