The increase in bilayer fluidity of rat liver plasma membranes achieved by the local anesthetic benzyl alcohol affects the activity of intrinsic membrane enzymes.

Abstract

Electron spin resonance studies on liver plasma membranes probed with a low concentration of 5-nitroxide stearate, 1(12,3), demonstrated that the local anesthetic benzyl alcohol increased the lipid fluidity, as indicated by decreases in the order parameter S. The fluidization commenced around 10 rn benzyl alcohol and increased up to the highest concentration tested (100 m).A lipid phase separation was identified between 19" and 28°C in 1(12,3)-1abeled liver membranes from Arrhenius-type plots of S. Both the onset and ending temperatures of the phase separation were lowered 6°C by 40 m M benzyl alcohol.At 37"C, low benzyl alcohol concentrations progressively activated the hepatic plasma membrane enzymes, glucagon-stimulated adenylate cyclase, basal adenylate cyclase, 5'-nucleotidase, cyclic AMP phosphodiesterase, and Na+,K+-ATPase.Fluoride-stimulated adenylate cyclase was also activated by low benzyl aicohol concentrations (up to 30 mM), except for an initial inhibition at 5 to 10 mM.Increasing the alcohol concentration above that which maximally stirnurated each of the above enzyme activities effected a progressive reversible inhibition.We propose that the stimulation of the membrane-bound enzymes at low benzyl alcohol concentrations was due to a fluidization of the lipid bilayer.The inhibition of enzyme activities observed at higher alcohol concentratians, which were not paralleled by such decreases in the activity of Lubrol-solubilized enzymes, is attributed to a displacement of lipid from around the enzymes (annular lipid) by benzyl alcohol.Membrane-bound and Lubrol PX-solubilized phosphodiesterase 1 were activated by benzyI aIcohoI (up to 100 mM) to similar degrees.On the other hand, benzyl alcohol did not increase the activity of either membrane-bound or Lubrol PX-solubilized Mg+-ATPase, but was instead a potent inhibitor of this activity in both preparations.These data indicate that membranebound phosphodiesterase 1 and Md'-ATPase are rela-