Abstract
Membrane preparations of rat hearts displayed specific binding activity for the prototypic sigma (σ) receptor ligand, 1,3-di(2-[5- 3H]tolyl) guanidine ([ 3H]DTG), but not for the phencyclidine (PCP) receptor ligand, [ 3H]MK-801. Scatchard plot analysis of [ 3H]DTG binding revealed the presence of one high affinity saturable binding site with a K D of 8.7 nM and a B max of 100 pmol/g protein. The drug specificity profile of the receptor correlated with that of the σ receptor with the following order of potency: DTG > haloperidol > (−)-pentazocine > (−)-butaclamol > (−) SKF-10047 . (+)pentazocine > PCP > TCP > MK-801 > (+)SKF-10047. [ 3H]DTG binding was sensitive to the Ca 2+ channel blocker, verapamil (K i 202 nM) but not to the K + channel blocker, 4-aminopyridine. The reverse stereoselectivity of [ 3H]DTG binding for (−)-SKF-10047 and (−)-pentazocine (K i of 1289 and 140 nM as compared with 17582 and 2190 nM for (+)-SKF-10047 and (+)-pentazocine, respectively) indicated that the heart contains σ receptors with characteristics of the σ 2 subtype.
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