Bis(7)-tacrine, a novel dimeric AChE inhibitor, is a potent GABA(A) receptor antagonist

Heptylene-linked bis-(9-amino-1,2,3,4-tetrahydroacridine) (bis(7)- tacrine) is a potential palliative therapeutic agent for Alzheimer's disease (AD), on the basis of its superior acetylcholinesterase (ACHE) inhibition and memory-enhancing potency relative to tacrine. In this study we report that bis(7)-tacrine exhibits a potentially complementary central nervous system action, antagonism of GABA(A) receptor function. Bis(7)tacrine displaced [³H]muscimol from rat brain membranes with an apparent K(i) of 6.0 μM; tacrine and physostigmine were shown to be 18 and 170 times less potent, respectively. In whole-cell patch-clamp recordings, bis(7)-tacrine inhibited GABA-induced inward current with an IC⁵⁰ of 5.6 μM, and shifted the GABA concentration-response curve to the right in a parallel manner. These results suggest that bis(7)-tacrine is a competitive antagonist of the GABA(A) receptor.