THE ESSENTIAL OIL FROM TAGETES-MINUTA L MODULATES THE BINDING OF [H-3]FLUNITRAZEPAM TO CRUDE MEMBRANES FROM CHICK BRAIN

The hypothesis that the essential oil from Tagetes minuta L. can inter act with biological membranes was investigated by assessing its abilit y of perturbing the binding of a benzodiazepine [flunitrazepam (FNTZ)] to crude membranes from chick brains. The essential oil from T. minut a L. inhibited [H-3]FNTZ specific binding to chick brain membranes. Th ese values were obtained from the analysis of the saturation curve for the kinetic parameters: dissociation equilibrium constant (K-d) = 2.4 7 +/- 0.32 nM, maximal binding (B-max) = 556 +/- 5 fmoles/mg protein, and Hill coefficient (n) = 1.00 +/- 0.07 in the absence, and K-d = 6.7 3 +/- 1.4 nM, B-max = 583 +/- 69 fmoles/mg protein, and n = 1.02 +/- 0 .08 in the presence of 29 mu g/mL of essential oil. The essential oil could self-aggregate with a critical micellar concentration (CMC) of 6 0 mu g/mL. The marked increase in [H-3]FNTZ nonspecific binding starti ng at 60 mu g of essence per mt was due to that phenomenon and reveale d the ability of self-aggregated structures to interact with membranes . [H-3]FNTZ specific binding decrement as a function of essence concen tration cannot be ascribed merely to oil's micelles ability of trappin g the lipophilic radioligand molecules, because the discontinuous beha vior that characterizes a monomer-aggregate phase transition was not s hown. Oil's components might behave as competitive inhibitors or allos teric modulators of FNTZ specific binding, However, their ability to i ncrease FNTZ nonspecific binding at concentrations below oil's CMC sug gests that this effect may be due to oil's partitioning into the lipid bilayer. This latter phenomenon would induce an increment in membrane fluidity and a change on FNTZ binding site toward a lower affinity co nformation. Therefore, the essential oil components can interact with brain membranes either as monomers, by partitioning into the lipid bil ayer, or as self-aggregated structures, through an adsorption to the m embrane surface.