Immunolocalisation of angiotensin II receptors in icefish (Chionodraco hamatus) tissues.

The monoclonal antibody 6313/G2 raised against the mammalian type I (AT1) angiotensin II (Ang II) receptor (Ang II-R) also recognises a component in teleost (eel) tissue preparations that binds radiolabelled Ang II, and has an isoelectric point (pI) of 6.5 and molecular mass of 75 kDa. Immunohistochemical analysis using this antibody showed specific binding sites in eel intestine, kidney, pill and liver sections. The same antibody was used here to evaluate the presence and distribution of Ang II-R in target tissues of the Antarctic teleost icefish (Chionodraco hamatus). Immunocytochemistry of intestine and gill sections showed that the antibody bound to uniformly distributed intracellular sites and cell surface membranes in absorptive cells in the intestine and chloride and pavement cells in the gills. It also stained endothelium and both the longitudinal and circular layers of smooth muscle cells in the intestine. In the kidney, only the tubules in the trunk stained positively while the head (atubular part of the kidney) was negative. In kidney tubules, in contrast with other tissues, the receptor was most concentrated in the cytoplasm underlying the basolateral membranes, with somewhat weaker staining beneath the apical cell membrane. Immunoblotting identified a single component from trunk kidney preparations that focused at pI 5.9 in isoelectric focusing gels and showed a molecular mass of 75 kDa in SDS-polyacrylamide gels. The data suggest that, as in other teleosts, Ang II has a physiological role in the icefish.