Immunocytochemical demonstration of vasopressin binding in rat kidney

Binding of a putative and a known chaperone protein revealed by immunogold labeling transmission electron microscopy: A suggested use of chaperones as probes for the distribution of their target proteins

Parvulins are a distinct family within the peptidyl-prolyl cis-trans isomerase group of proteins that catalyse the cis-trans isomerization of proline-containing peptides. The intracellular distribution of a novel human parvulin homologue (hEPVH) has been investigated in a human kidney cell line (HEK 293) by immunogold labeling transmission electron microscopy (TEM). This showed hEPVH to be distributed throughout HEK 293 cells but in highest concentration within mitochondria. Unexpectedly, preabsorption of anti-hEPVH antiserum with recombinant hEPVH exaggerated the observed immunolabel density in a pattern that mirrored that of the endogenous hEPVH. The hEPVH protein itself was then used to label sections, and the specificity of its binding was confirmed with the use of polyclonal and monoclonal antibodies in conjunction with homologous and irrelevant protein controls. The pattern of hEPVH binding also mirrored that of endogenous hEPVH. A known chaperone protein, Pin1, was also found to bind to cells in a pattern mirroring that of the endogenous protein. This lends considerable weight to our hypothesis that hEPVH is binding to its target protein(s) within the cell, reflecting its postulated chaperone function. Finally, we suggest that chaperone proteins in general might be used as TEM probes for their target (or substrate) proteins. (J Histochem Cytochem 47:1633-1640, 1999)

Immunolocalization of V1 vasopressin receptors in the rat kidney using anti-receptor antibodies

By using immunocytochemical techniques we have been able to localize the V1 vasopressin receptor in the rat kidney. Immunoblotting using an antiserum raised against an affinity-purified vasopressin receptor showed a 55,000 daltons protein band that has a molecular mass similar to that of the liver V1 vasopressin receptor, as demonstrated by cross-linking studies. Immunoblotting of the antibody showed a band of 55,000 daltons in A-10 cells, which contains the V1 subtype, whereas it did not stain LLC-PK1 cells, which possess the V2 subtype, showing that the antibody recognizes the V1 vasopressin receptor. The immunostaining of kidney sections with this antiserum showed a strong reaction of the connecting tubules and cortical and medullary collecting ducts. The immunostaining pattern of connecting tubule and collecting duct cells was different, that is, the former showed a staining of both the apical and basal plasma membrane but also in the cytoplasm, whereas the latter showed a strong reaction mainly in the basolateral membrane. Immunostaining of consecutive serial sections with an antiserum raised against tissue kallikrein, an enzyme present exclusively in connecting tubules, and with the anti-receptor serum allowed us to show, for the first time, the presence of the vasopressin receptor in the connecting tubule cells and their absence in intercalated cells, the other cell type present in connecting tubules. These findings support experiments carried in the eighties on the release of renal tissue kallikrein by AVP.

Fluorescent analysis in polarized MDCK cell monolayers: intracellular pH and calcium interactions after apical and basolateral stimulation with arginine vasopressin

Intracellular calcium ([Ca2+]i) and hydrogen ion concentrations (pHi) are important regulators of cell function. Those ions also may interact and it is important, therefore, to measure their concentrations simultaneously. In the present studies we used a system developed for that purpose, a fluorescent emission ratio technique for simultaneous analysis of calcium (Indo-1) and pH (SNARF-1) in single cells at video rates, and determined if arginine vasopressin (AVP, 12.5 mumol/l) evoked [Ca2+]i and pHi signals interact in MDCK cells. We also employed a simple system for analysing the side specific (basolateral or apical) application of agonist to polarized cell layers on permeable membranes. AVP is found to evoke simultaneous changes in both pHi and [Ca2+]i. Basolateral application induced transient acidification, followed by partial recovery, and a [Ca2+]i transient with kinetic pattern similar to that of the pHi. Apical application also caused a mirror image pHi and [Ca2+]i pattern but of smaller magnitude (no peak). Selective removal of extracellular calcium ([Ca2+]e) or sodium ([Na+]e) dissociated the pHi and [Ca2+]i responses in both cases. Na+e removal abolished the pHi changes, but not the [Ca2+]i transients. [Ca2+]e removal abolished the [Ca2+]i changes and reduced, but did not abolish, the pHi responses. Thus, AVP induces pHi changes which are modified by calcium while calcium signalling is not modified by changes in pHi.

Renal and central vasopressin receptors: immunocytochemical localization

Employing an anti-vasopressin monoclonal antibody for immunization, anti-idiotypic monoclonal antibodies were obtained which induced plasminogen activator production in the renal epithelial cell line LLC-PK1. The anti-idiotypic antibodies were employed to visualize vasopressin receptors on LLC-PK1 and A7r5 smooth muscle cells by immunofluorescence. All results indicated specificity of the anti-idiotypes for both V1 and V2 vasopressin receptor subtypes. These antibodies were used for immunohistochemical localization of vasopressin receptors in rat and bovine kidney preparations. In accordance with earlier physiological and biochemical observations, vasopressin receptors were detected predominantly in collecting ducts in cortex and medulla. On the cellular level, a differential staining pattern was observed. On rat brain tissue sections, dense staining was observed within various circumventricular organs. The staining pattern corresponded to that obtained in autoradiographic studies with labeled AVP(4-9) fragment peptide and differed from the distribution of binding sites for labeled vasopressin or V1 antagonists.

Generation of anti-idiotypic monoclonal antibodies recognizing vasopressin receptors in cultured cells and kidney sections

To produce anti-idiotypic antibodies against receptors for the neurohypophyseal hormone vasopressin, an anti-vasopressin monoclonal antibody with a ligand specificity similar to that of vasopressin receptors was employed for immunization. Three anti-idiotypic monoclonal antibodies were obtained which induced, like vasopressin, plasminogen activator production in the renal epithelial cell line LLC-PK1 (expressing V2-receptors). Induction of plasminogen activator synthesis by the anti-idiotypic antibodies could be inhibited by coincubation with a vasopressin antagonist. In a fashion similar to that of vasopressin itself, the anti-idiotypic antibodies induced receptor down-regulation. The anti-idiotypic antibodies were employed to visualize vasopressin receptors on LLC-PK1 and A7r5 (V1-receptor-expressing) smooth muscle cells by immunofluorescence. Antibody-mediated fluorescence was not observed in receptor-deficient mutant cell lines or vasopressin-receptor-down-regulated cells. Furthermore, these antibodies were used for immunohistochemical localization of vasopressin receptors in rat and bovine kidney preparations. In accordance with earlier physiological and biochemical observations, vasopressin receptors were detected predominantly in collecting ducts in cortex and medulla. On the cellular level, a differential staining pattern was observed.