Molecular Pharmacology, Vol 17, 290-294, Copyright © 1980 by the American Society for Pharmacology and Experimental Therapeutics

Effect of Calcium and Physical State of Neutral Membranes on Phosphatidylserine Requirement for Opiate Binding

¹ Center for Brain Research and Department of Biochemistry, University of Rochester Medical Center, Rochester New York 14642

A study was undertaken to investigate the nature of the inhibitory action of phospholipase A₂ (PL-A) on stereospecific opiate binding to rat brain membrane preparations in relation to the hypothesis that phosphatidylserine (PS) is required for binding. Although the presence of albumin will prevent the inhibitory effect of PL-A, the protective action of the protein is substantially less at higher enzyme concentrations, which result in over 10% reduction of the endogenous PS. PS is able to restore opiate binding after exposure to lower, but not higher, concentrations of the enzyme. In the presence of albumin, the enhancement effect of PS is not demonstrable, presumably because the albumin conjugates the lipid. The presence of Ca or other multivalent cations is not required for the enhancement effect of PS, as evidenced by the fact that the repeated washing of the membranes by EGTA or EDTA does not alter the extent of enhancement. Opiate binding was greatly reduced by physical disruption of membranes by either freeze-thawing or sonication, while in each case the addition of PS restored binding to the control level.