TISSUE AND CELL, 1994 26 (1) 75-81 fQ 1994 Longman Group UK Ltd. HUBERT H. KERSCHBAUM”, SHIO KUMAR SINGH*t, and ANTON HERMANN” PARVALBUMIN-IMMUNOREACTIVE MATERIAL IN THE KIDNEY OF XENOPUS LAEVK Keywords: Parvalbumin. calcium-binding proteins. immunohistochemistry, kidney. Xenopus ABSTRACT. Parvalbumin-immunoreactive material has been localized in various parts of the Xenopus kidney. Ciliated epithelia in the neck segment, the intermediate segment and in the peritoneal funnel, epithelial cells intermingled among flask cells in the connecting tubule, and cells in the proximal and distal tubules cells were labelled. Renal corpuscle and collecting duct cells did not exhibit parvalbumin immunoreactivities. Western-blot analysis of kidney homogenates indicated various isoforms of parvalbumin-immunoreactive proteins. zyxwvutsrqponmlkjih Introduction Cal+ plays an important role in various trans- port processes in epithelial cells (Carafoli, 1991; Lang and Rehwald, 1992). For example, in kidney tubule cells Ca*+-depen- dent ion conductances and stretch-activated channels permeable to Ca*+ mediate the coupling between K+ secretion and Na+ absorption and provide a transport pathway from the cell to the lumen in collecting ducts (cf. Guggino, 1987; Lang and Rehwald, 1992). Similar to many other cells, kidney cells exhibit a low intracellular resting Ca*+ concentration (Dantzler, 1989) indicating the presence of a powerful system for Ca*+ regu- lation. Proteins which specifically interact with Ca*+ are in many cases involved in buffering of Ca*+ and in the operation of target proteins which govern the uptake and extrusion of ions and other secretatory prod- ucts (cf. Heizmann and Braun, 1990; Wein- *University of Salzburg, Department of Animal-Physi- ology, Institute of Zoology, Hellbrunnerstr. 34, A-5020 Salzburg, Austria, *Department of Zoology, Banaras Hindu University, Varanasi 221005, India. Correspondence to: Prof. Dt A. Hermann. Received 24 May 1993 Revised 10 August 1993 mann, 1991; Donato, 1992). Parvalbumins are calcium-binding proteins which, due to their helix-loop-helix motif of the Ca*+-bind- ing site, are categorized as EF-hand proteins (cf. Heizmann, 1984; Moncrief et al., 1990). These proteins are present in specific cell populations in various tissues, such as the nervous system and muscle (cf. Heizmann and Hunziger, 1991; Andressen et al., 1993) where they have been postulated to be involved in the generation or modulation of cellular activities by predominantly buffering intracellular Ca2+. In the kidney parvalbumin has been reported only in the rat (Schneeberger and Heizmann, 1986), but not in any other ver- tebrate species.Rats, like all other mammals, as well as most adult amphibians are ureotelic animals, who produce urea as excretion prod- uct. Due to its aquatic life, the clawed frog, Xenoplcs laeuis. however, even as adult, pre- dominantly excretes ammonia (Dantzler. 1989) which may have consequences for Ca*+-dependent transport properties of kid- ney cells. In this study we have investigated the localization of parvalbumin in the Xenopus kidney, in order to compare its distribution with that of the rat kidney and to correlate parvalbumin-immunoreactive cells with possible Ca2+-dependent activities. 75