Interactions of adrenergic compounds with brain membrane constituents

The specific activity of the Na+, K+-ATPase of rat brain synaptosomes was modulated by a series of adrenergic compounds in a manner related to each compound's partition between aqueous and organic solvents. The more organic-soluble compounds, the β-2 adrenergic blockers propranolol, pronethalol and butoxamine, inhibited the enzyme between 13 and 30 per cent. The more aqueous-soluble compounds, the agonists, epinephrine, norepinephrine and isoproterenol, and the β-1 blockers, practolol and acebutolol, stimulated the enzymatic activity by 30 per cent. These effects may be due to non-specific membrane interactions rather than to specific receptor effects. Optical measurements with pure protein and phospholipid indicated that the aqueous-soluble compounds bound to protein while the organic-soluble compounds interacted with acidic phospholipid phosphatidyl serine. The possible consequences of the compounds binding with acidic phospholipids and the resulting effect on membrane properties are discussed.