Molecular Pharmacology, Vol 12, 115-126, Copyright © 1976 by the American Society for Pharmacology and Experimental Therapeutics

Effects of Cations and Propranolol on a Fluorescent Phospholipid Incorporated into Brain Synaptosome Membranes

¹ Neurochemistry Laboratory, Veterans Adminstration Hospital, and Departments of Medicine (Neurology) and Physiology and Biophysics, University of Washington School of Medicine, Seattle, Washington 98108

Dimethylaminonaphthalenesulfonyl-phosphatidylserine (DNS-PS), a fluorescent phospholipid, was incorporated into rat brain synaptosomes by a procedure utilizing the chaotropic agent sodium perchlorate. This procedure caused only minor changes in the electron microscopic appearance and protein composition of the membranes. Perchlorate treatment alone altered the activity of selected enzymes such as acetylcholinesterase and monoamine oxidase, but the insertion of DNS-PS within the membrane had only minor effects on the specific activities of synaptosomal enzymes. The fluorescence emission maximum of the membrane-bound DNS-PS was shifted to a slightly longer wavelength by addition of 100 mM NaCl or KCl, and the polarization of fluorescence decreased. The addition of 10 mM CaC1₂ shifted the emission maximum to a shorter wavelength, increased relative fluorescence 10-20%, and increased the polarization of fluorescence. Energy transfer from aromatic residues of membrane proteins to the DNS moiety was increased 11% by CaCl₂, while MgCl₂ had little effect, suggesting that Ca²⁺ may decrease the intermolecular distance between aromatic amino acids of membrane proteins and the fluorescent phospholipid. The beta adrenergic blocking agent propranolol reversed the changes caused by calcium and displaced at least a portion of the bound cation from the membrane.

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ACKNOWLEDGMENTS We thank Dr. Phil Smith for electron microscopic examinations of synaptosome preparations, and W. D. Northcroft of Ayerst Laboratories for the propranolol.