USE OF A SPREADSHEET TO QUANTITATE THE EQUILIBRIUM BINDING OF AN ALLOSTERIC MODULATOR

Using the program Microsoft EXCEL, a spreadsheet was developed for con strained, simultaneous analysis of multiple datasets obtained from equ ilibrium binding experiments, according to an allosteric model of inte raction. This approach was used to quantitate the interaction between the modulator (heptane-1,7-bis (dimethyl 3'-phthalimidopropyl) ammoniu m bromide) (C-7/S-phth) and the radioligands [H-3]N-methylscopolamine and [H-3]quinuclidinyl benzilate at cortical and atrial muscarinic rec eptors. The interaction between various concentrations of the radiolig ands and C-7/3-phth, in the guinea pig atrium and in the rat cerebral cortex, could be well described by the allosteric model. The affinity of C-7/3-phth for unoccupied atrial receptors was significantly higher than for cortical receptors. The negative cooperativity between [H-3] quinuclidinyl benzilate and the modulator was higher in cortex than th at between the modulator and [H-3]N-methylscopolamine. It is suggested that the described method has wide applicability because of the exten sive availability of spreadsheet programs, the analytical advantages o ffered by constrained, simultaneous nonlinear regression and the abili ty to adapt the spreadsheet to almost any model of ligand-receptor int eraction. (C) 1998 Elsevier Science B.V. All rights reserved.