Increased fluidity of a model membrane caused by tetrahydro-beta-carbolines

Alterations in membrane fluidity caused by alcohols and tetrahydro-beta-carbolines (THBCs) have been studied. Dipalmitoylphosphatidylcholine vesicles were used as a membrane preparation, and changes in the fluidity were revealed by two fluorescent probes: 1-anilinonaphthalene-8-sulfonic acid (1,8-ANS) and N-phenylnaphthylamine (NPN). It was found that THBCs, which are condensation products of tryptamine and formaldehyde or acetaldehyde, were at least 2 orders of magnitude more potent in causing fluidity changes than the comparable alcohols (methanol and ethanol). Both 1,8-ANS (binding close to the polar end of the phospholipid molecules) and NPN (binding to the hydrophobic region of the membrane) were able to reveal changes in membrane fluidity, although there were differences between the behavior of the two probes. The condensation product of acetaldehyde--the primary metabolite of ethanol--and tryptamine were found to be 200-300 times more potent in causing fluidity changes than ethanol itself (as determined with both 1,8-ANS and NPN).