Publication Abstract

Characterisation of putative steroid receptors in the membrane, cytosol and nuclear fractions from the olfactory tissue of brown and rainbow trout

Characterisation of putative steroidreceptors in the membrane, cytosol and nuclear fractions from the olfactory tissue ofbrown and rainbow trout

T.G. Pottinger and A. Moore

Specificbinding sites for testosterone have been detected in three compartments of olfactorytissue from brown and rainbow trout. Binding of ³H-testosterone to the membranefraction of olfactory tissue is of high affinity (K_d = 0.5-1.9 nM) and limitedcapacity (N_max = 30-60 fmol mg^-1 protein). Binding is reversible,and is eliminated by protease treatment. The membrane binding site exhibits a high degreeof ligand specificity; 11β-hydroxytestosterone, 11-ketotestosterone, 17α-hydroxyprogesterone,17α,20β-dihydroxy-4-pregnen3-one,cortisol, and estradiol-17β all fail to displace testosterone at 20-fold excess while testosterone itselfcompetes successfully. These attributes are consistent with the presence of specificsteroid receptor proteins. Binding of testosterone within the cytosol is of moderateaffinity (K_d = 9.0-23.0 nM) and high capacity (N_max = 0.5-2.9 pmolmg^-1 protein) and is more readily displaced by a number of steroid competitorsthan is the case for the membrane site. The rate of association and dissociation oftestosterone from the cytosolic binding site is markedly more rapid than the equivalentprocesses in the membrane fraction. Binding of testosterone to the nuclear extract is ofhigh affinity (K_d~ 3.0 nM) and limited capacity (Nmax ~50 fmol mg^-1protein).

There are no substantial differencesbetween species or between sexes in the affinity or capacity of testosterone-binding sitesin nuclear extract or membrane fraction. However, cytosolic testosterone-binding sites arethree- to four-fold more abundant in rainbow trout than in brown trout, and female rainbowtrout have more cytosolic binding sites than male rainbow trout, but a lower affinity fortestosterone than male sites.

Preliminary evidence supports theinvolvement of the membrane-associated testosterone-binding site in olfactory processes.Rainbow trout display an EOG response to testosterone at a concentration (10^-9 M) which isconsistent with the equilibrium dissociation constant (K_d) of themembrane-associated testosteronebinding site. Binding of 'H-testosterone to themembrane-associated site shows a pH dependency which is comparable to the effects of pH onthe EOG response to testosterone in intact fish. The attributes of the intracellulartestosterone-binding sites are common to testosterone receptors in other fish tissueswhich are known androgen target tissues. This suggests that the development and/orfunction of salmonid olfactory tissue may be susceptible to influence by endogenoustestosterone.

Reference:

T.G. Pottinger and A. Moore, 1997. Characterisation of putative steroid receptors in themembrane, cytosol and nuclear fractions from the olfactory tissue of brown and rainbowtrout. Fish Physiology and Biochemistry, 16(1): 45-63.

T.G. Pottinger and A. Moore*

Fish Physiology and Biochemistry, 16(1): 45-63