halfway through the incubation incubations are terminated by filtration through 2 4 cm gf b filters under reduced pressure each tube is filtered as follows the contents of the tube are poured on the filter 4 ml of ice cold tris are added to the tube and the contents poured onto the filter and the filter is washed twice with 4 ml of ice cold tris the filtration is complete in about twelve seconds filters are put in scintillation vials 8 ml of formula 947 scintillation fluid added and the vials left overnight shaken and counted in a liquid scintillation counter at 40 efficiency nonspecific binding is defined as binding in the presence of 100 u03bcm n6 cyclopentyladenosine and specific binding is defined as total binding minus nonspecific binding the ic 50 is calculated by weighted nonlinear least squares curve fitting to the mass action equation equ3 where weighting factors are calculated under the assumption that the standard deviation was proportional to the predicted value of y nonspecific binding is treated as a very large infinite concentration of drug in the computer analysis the ic 50 values nm for adenosine a 1 and a 2 receptor affinity are reported in the table i table i______________________________________receptor binding dataexample rba 1 nm rba 2 nm ______________________________________1 331 77702 71 61303 49 7 25104 68 50805 101 gt 1000006 487 66307 109 23208 146 58809 74 869010 554 4070011 982 2000013 12 5 2080______________________________________ for preparing pharmaceutical compositions from.