The Presence of σ-Receptors in the Lacrimal Gland

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Abstract
Applying the technic of S.A. Wolfe et al. [Endocrinology, 124, 1160-1172, 1989], we have established the presence of sigma receptors in isolated, but intact, lacrimocytes excised from main lacrimal gland tissue of the New Zealand white rabbit. 3H-Haloperidol was used as the ligand (0.5-2500 nM), in the presence of spiperone. From a Scatchard plot, a single binding site was statistically chosen over two sites for a majority of the data associated with the intact lacrimocytes. Kd (71.0 ± 46.4 nM) and Bmax (588.2 ± 166.7 fmol/mg of protein) values showed lower binding affinity but a similar density of sigma sites in rabbit lacrimocytes when compared to published results obtained for rat exocrine glands and brain tissue. Using the technic of McCann and Su [J. Pharm. Exp. Therap., 257, 547, 1991], membrane suspensions of the sigma receptor were also prepared and tested for binding to radioligands, 3H-DTG, as well as 3H-haloperidol. A Scatchard plot revealed two binding sites for 3H-DTG and one binding site for 3H-haloperidol. The high affinity site for 3H-DTG yielded a Kd of 1.04 ± 0.64 nM, whereas, Bmax was 135.9 ± 11.62 fmol/mg of protein. The low affinity site gave a Kd = 75.3 ± 26.8 nM and Bmax = 344.0 ± 222.0 fmol/mg of protein. The weaker site is suspected to be intracellular. IC50 values were determined for N,N-disubstituted arylphenylalkylamines (Kd = low nM).