SUBCELLULAR-LOCALIZATION OF STERO-SPECIFIC OPIATE BINDING IN MOUSE-BRAIN

  • 1 January 1976
    • journal article
    • research article
    • Vol. 15  (2) , 205-219
Abstract
Of the 3 primary sub-cellular fractions derived from mouse brain homogenates, the P3 (microsomal) fraction binds 3H-dihydromorphine stereo-specifically with the highest capacity per mg of protein; this level is nearly as great as that bound by purified synaptosomal plasma membranes (SPM). The binding of P3 is unlikely to be attributable to contamination with SPM, because 10 times as much total binding is recovered in P3 as in SPM, and the level of binding to P3 is highest in a sub-fraction banding above 0.8 M sucrose, rich in surface membranes of all types; SPM bands preferentially at 0.8-1.1 M sucrose. The binding of either 3H-dihydromorphine or 3H-naloxone to P3 is indistinguishable from that found in nerve endings with respect to its Kd, the relative potencies of several agonists in displacing it and the effects on it of Na+ or trypsin. Stereo-specific opiate receptors are distributed diffusely on the entire surface of nerve cells and not concentrated at the synaptic region as was previously supposed.