Whole body autoradiography and microautoradiography in eels after intra-arterial administration of 125I-labeled eel ANP.

125I-labeled eel atrial natriuretic peptide (ANP) was administered into the ventral or dorsal aorta of freshwater (FW) and seawater (SW) eels, Anguilla japonica, and the major target organs were explored by whole body autoradiography. Localization of the ANP binding in the target organs was also examined at tissue and cell levels by microautoradiography using tissue sections. Whole body autoradiography revealed that the specific label was accumulated predominantly in the gill, with lesser amounts in the atrium, kidney, liver, and urinary bladder. Autoradiographic grains were most dense in the secondary lamellae of the gill, particularly on the side of the efferent filamental artery. Other binding sites in target tissues were the glomerulus of the kidney, epicardium and endocardium of the atrium, bile duct/blood vessels of the liver, and interrenal cells of the head kidney. There was no difference in the distribution and density of grains between injections into the ventral aorta and dorsal aorta, although, in the former, injected 125I-labeled eel ANP passes through the gill before reaching peripheral target tissues. There was a tendency for downregulation of ANP binding sites in SW eels, especially in the gill. These results show that specific ANP binding sites are present in organs that are implicated in osmoregulation and cardiovascular regulation in eels and further suggest that the number of ANP binding sites varies according to changes in the environmental salinity.

Perichondrial localization of ETA receptor in rat tracheal and xiphoid cartilage and in fetal rat epiphysis.

Autoradiographic studies using 125I-labeled endothelin-1 (ET-1) on sections of rat cartilage tissues, including the trachea, xiphisternum, and fetal rat epiphysis, revealed dense localization of endothelin receptors in the perichondrium. In contrast, the binding of ET-1 was not detected in the chondrocytes, cartilage matrix, and other connective tissues of the cartilage tissues tested. The perichondrial binding of 125I-ET-1 was completely abolished with BQ-123 [an endothelin receptor subtype A (ETA) antagonist] but not with BQ-3020 (an ETB agonist), and we demonstrated the perichondrial localization of ETA receptors. [3H]thymidine incorporation in vitro was significantly increased in rat xiphoid cartilage tissues exposed to ET-1. These findings suggest that the ET-1/ETA receptor system plays an important role in regulating cartilage metabolism and endochondral bone formation.

Solubilization of endothelin receptors from bovine lung plasma membranes in a non-aggregated state and estimation of their minimal functional sizes.

Bovine lung endothelin receptors were solubilized in a non-aggregated state and characterized in terms of their minimal functional size and chemical nature of the ligand-binding site. A variety of detergents and their combinations were tested for their efficiency to solubilize endothelin receptors from bovine lung plasma membranes, and a combination of 0.4% digitonin and 0.25% CHAPS was found to be very effective in obtaining highly dispersed receptor solution. Gel filtration of the CHAPS/digitonin-solubilized receptors revealed the presence of two receptor species eluting at the positions corresponding to 34 and 52 kDa. These values were in good agreement with those estimated by affinity labeling and SDS-polyacrylamide gel electrophoresis, establishing that they represent minimal functional units. Chemical modification of ligand-occupied and free receptors with p-chloromercuriphenylsulfonic acid revealed that both 34 and 52 kDa receptors have SH group(s) essential for the receptor activity in their ligand-binding sites.

Water and potassium ion absorption by deuterium oxide resistant winter rye seedlings.

The concentrations of deuterium oxide (D2O) in the root tissue water of winter rye seedlings equilibrated with the external D2O concentration within 30 min and in the shoot tissue water after 5-6 h. The equilibrated value in the root water was 87% and in the shoot water, 55% of the external concentration. The K+ absorption rate of the seedlings decreased from a value of 39 to 18 mumol g-1 h-1 when the D2O concentration was changed through a range from 0% to 97%. D2O suppressed the absorption of water and K+ by the seedlings. The higher the D2O concentration the greater the suppression, but it was less than with similarly treated rice plants. However, the process of D2O absorption by the seedlings was similar to that of rice seedlings (Envir. exp. Bot., 24, 369).

Hydrogen isotope effect on transport of potassium ion in rice seedlings equilibrated with deuterium oxide.

Potassium absorption by the root of rice seedlings, equilibrated with D2O before K+-absorption, decreased proportionally with D2O concentration and the translocation of the absorbed cations by roots to shoots decreased markedly above 40% D2O. An inhibition curve for the absorption process drawn as a relative rate vs. D2O concentration exhibits no threshold in concentration of D2O. While K+-absorption of the seedlings unequilibrated with D2O did not change up to 60% D2O and decreased above 80%. The concentration of D2O of root tissue water reached a balance with the external concentration within 30 min, but the concentration of shoot water required 5-6 h to balance with the external. The concentration of both root and shoot water did not coincide with the external. The suppressive effect of D2O on potassium absorption links not only to D/H ratio in root water but also in shoot water.

Transport of calcium, germanium and rubidium ions in rice seedlings in deuterium oxide.

Deuterium oxide affected all types of transport processes of ions in rice seedlings. The processes of the active transport of Rb+, the passive diffusion of Ca2+, and the preferential and specific absorption of Ge by the seedlings in D2O solutions, were suppressively distorted by D2O. The suppressive effect on the translocation of all ions studied and the absorption of Rb+, was greater with higher concentrations of D2O. However, clear-cut relations of the effect of increasing D2O concentrations on the ion transport were not obtained. The extent of the replacement of H2O by D2O in the plant appeared to affect the movement of ions in the plant.