Search Results

ABSTRACT

Immunocytochemistry of paraffin-embedded and cryostat sections of eel (Anguilla anguilla) gill showed that angiotensin II receptors (Ang II-R) were present in chloride cells, uniformly distributed in the cytoplasm and on surface membranes. Computerised image analysis of these preparations showed that gills from sea water (SW)-adapted animals had a significantly (3-fold) higher Ang II-R concentration compared with freshwater (FW)-adapted eel gills. Isoelectric focusing gel electrophoresis revealed two Ang II-R isoforms with pI 6·5 and 6·6 that were differentially modulated by environmental salinity: they were equally abundant in SW while in FW the pI 6·6/pI 6·5 ratio was 1·66.

Using catalytic cytochemistry with image analysis, gill chloride cell membrane Na⁺/K⁺ATPase activity was shown to increase 4-fold in response to SW adaptation. Additionally, perfusion of gills for 30 min with 0·1, 10 or with 100 n_M Ang II provoked a dose-dependent increment in Na⁺/K⁺ATPase activity in FW, and a biphasic response in SW gills in which activity was significantly increased at low Ang II concentrations but was reduced to basal values at 100 n_M.

The data suggest that adaptation to sea water significantly increases Ang II-R concentration in the chloride cell and, together with the effects of Ang II on Na^+/K⁺ATPase activity, suggest a role for this hormone in gill NaCl retention. The different responses of Na⁺/K⁺ATPase to Ang II stimulation in FW and SW may be attributed to the presence of two receptor subtypes that are differently modulated by salinity and that have opposing effects on Na⁺/K⁺ATPase.

ABSTRACT

We evaluated the presence and variability of oestrogen receptor (ER) isoforms in endometrial cancer by using [³H]oestradiol-labelled ERs and the H222 monoclonal antibody obtained from the Abbott enzyme immunoassay kit.

Using isoelectric focusing (IEF), endometrial ER was shown to be composed of four different species, with pI values of 6·1, 6·3, 6·6 and 6·8, indistinguishable from the isoforms found in normal rat uterus, and human breast and larynx carcinomas. The isoforms at pI 6·3, 6·6 and 6·8, all sedimenting at 4S by sucrose gradient fractionation, showed, on two-dimensional SDS electrophoresis, relative masses of 50, 70 and 65 kDa respectively, equal to the masses previously found in breast cancer. These isoforms did not alter their pI values during IEF fractionation performed in a linear gradient of urea, while the pI 6·1, sedimenting at 8S, generated a new isoform at about 9 mol/l urea with pI 7·2 and a relative mass of 65 kDa. The urea-dissociated isoform (pI 7·2) was able approximately to double the antibody binding with respect to the non-dissociated oligomer, which suggested that some epitopes are 'masked', i.e. not accessible to the antibodies when ER is present in its complexed form. The evidence thus suggested that the oligomer at pI 6·1 contained a single 65 kDa ER form which, as a monomer, focused at pI 7·2.

The variability in the ER isoform profile found in endometrial cancer was similar to the variability previously reported in breast and larynx carcinomas. The balance between these isoforms could be a dynamic parameter involved in the functionality of this receptor and consequently in cell transformation.

ABSTRACT

The pH-sensitive fluorescent dye, 2′,7′-bis-carboxy-ethyl-5,6-carboxyfluorescein acetoxymethyl ester, was used to examine the effects of fish or human angiotensin II (Ang II) on the activity of the basolateral located Na⁺/H⁺ antiporter in eel intestinal cell suspensions. Exposure of eel enterocytes to either hormone led to an increased activity of the antiporter. This time- and dose-dependent stimulatory effect was inhibited by the specific antiporter inhibitor dimethylamiloride (DMA).

Preincubation with a monoclonal antibody (6313/G2), directed against the N-terminal extracellular domain of the mammalian AT₁ Ang II receptor, prevented the stimulatory effect of the hormone and inhibited the binding of [3,5-³H]Tyr⁴-Ile⁵-Ang II to intestinal cell suspensions, suggesting specific binding of the antibody to the eel Ang II receptor. The results indicate that both fish and human Ang II stimulate the DMA-sensitive Na⁺/H⁺ antiporter present in eel intestinal cells by means of a mammalian AT₁-like receptor.

ABSTRACT

Using labelled ligand-binding methods, previous studies have identified specific angiotensin II receptors (Ang II-Rs) in eel liver, kidney and intestine membranes. Isoelectric focusing on polyacrylamide gels also showed that there are two Ang II-R isoforms in eel liver, focusing at isoelectric points (pI) 6·5 and 6·7. These may have different functions. In contrast, eel enterocyte plasma membrane and renal brush border membranes contain only the pI 6·5 form.

To characterize the eel receptors more fully, a newly developed monoclonal antibody (6313/G2) which selectively recognizes the AT₁ subtype of mammalian Ang II-R was used. In ligand-binding experiments, the preincubation of eel liver membranes with 6313/G2 antibody eliminated the specific [3,5-³H]Tyr⁴-Ile⁵-Ang II binding. Moreover, Ang II—receptor complexes from solubilized liver membranes, which were immunoprecipitated by 6313/G2-coated beads, had a pI of 6·5. In immunoblotting experiments, the antibody recognized the isoform focusing at pI 6·5 in eel intestine and liver preparations, but not the liver pI 6·7 isoform. Immunoblotting of SDS gels showed that the antibody bound to a single protein of molecular mass of 75 kDa in eel liver, gill and kidney and to a doublet of molecular mass of about 74 and 75 kDa in intestinal membrane preparations. Immunocytochemistry of paraffin-embedded and cryostat sections of eel liver, kidney, intestine and gill showed that antibody 6313/G2 bound to uniformly distributed intracellular sites and cell surface membranes in proximal tubular cells, absorptive intestinal cells, hepatocytes and chloride cells. It also stained endothelium and both the longitudinal and circular layers of smooth muscle cells in the intestine.

The data suggest that the previously described Ang II-R from eel liver, kidney and intestine may be similar to the mammalian AT₁ subtype.