Receptor analysis: an arithmetic correction improves precision and accuracy

Androgen receptors in prostatic tissue: evaluation of systematic errors and comparison of three procedures to correct for nonspecific binding sites in the binding assays

In androgen receptor analysis, nonspecific binding can distort the measurement of the binding constants of the receptor ligand complex. We evaluate this influence with a one-ligand two-binding sites model. The binding constants correspond to those of androgen receptors in prostatic tissue. Three procedures which correct for the influence of nonspecific binding sites are compared: difference of bound radioligands measured in both assays (assay 1: only radioligand, assay 2: additional unlabelled ligand in excess), nonlinear regression, and difference of bound radioligands corrected by the ratio of the free radioligands. The subtraction of bound radioligands causes considerable errors in the estimation of the total concentration of receptor binding sites. Nonlinear regression yields the correct result when the influence of nonspecific binding is moderate. The corrected difference of bound ligand gives the correct results even in the range where nonlinear regression fails. We conclude that the latter method corrects for the influence of nonspecific binding as effectively as nonlinear regression and suggest that the free fraction of radioligand should be measured and not discarded, as it is common in the clinical practice.

Receptors for atrial natriuretic peptide (ANP) and cyclic GMP responses in HeLa cells

Cultured HeLa cells display specific binding sites for atrial natriuretic peptide (ANP). Studies with [125I]-(1-28)-rat ANP revealed the presence of a single class of high affinity binding sites on HeLa cells: The apparent dissociation constant (Kd) was 5 nM and the maximal number was 29,000 sites/cell as derived from Scatchard analysis. Furthermore, ANP elevates levels of cGMP in a dose dependent manner with an EC50 close to the Kd for [125I]ANP binding. ANP-mediated elevation of cellular cGMP leads to a significant reduction of bumetanide-sensitive Na+, K+, 2Cl(-)-cotransport in HeLa cells, studied by 22Na+ and 86Rb+ influx measurements. These data indicate (1) that distinct functionally active receptors for ANP are present on HeLa cells and (2) ANP influences the activity of Na+,K+,2Cl(-)-cotransport in these cells.

Seasonal and diurnal changes of prostatic androgen receptor and circulating testosterone in young mature rats

Low- and high-salt (600 mM KCl) extractable androgen receptors were measured in the ventral prostate lobes of 70-day-old rats which were housed in constant environmental conditions (22 +/- 2 degrees C, 65 +/- 5% air humidity, light 6.00h-18.00h). Seasonal variations were observed during 2 years, exhibiting elevations in late summer and autumn and depressions in late winter and spring time. These fluctuations were superposed by steep changes from month to month. The maximum and minimum values of the low- and high-salt extractable receptors differed within 1 year by a factor 8.5 and 2.4, respectively. Both receptor fractions showed a diurnal rhythm as measured during 1 day in January with maximal concentrations at 9.00 h (low-salt: median = 1308 fmol/mg DNA) and minimal values at 18.00 (424) and 24.00 (230). The electrophoretic mobility in agar gel of pH 8.2 also showed a diurnal variation with maximal values at 18.00 h in either receptor fraction. Neither the seasonal nor the diurnal variations were correlated to the corresponding rhythms of serum testosterone concentrations. As steroid receptors may be regulated by neural transmission, in a final experiment the parasympathic innervation of the prostate was blocked by infiltrating the plexus pelvicus with a local anesthetic drug. One hour later, the total receptor concentration was not changed, while the ratio of low- to high-salt extractable receptors and the electrophoretic mobility of both fractions were elevated as compared to the control animals. This finding indicates that peripheral neural transmission rather than circulating testosterone may be involved in the regulation of androgen receptors in rat ventral prostate.