Characterization of a Na +-K +-2Cl − cotransport system in oocytes from Xenopus laevis

Abstract

In order to characterize the transport systems mediating K + uptake into oocytes, flux studies employing 86Rb were performed on Xenopus oocytes stripped of follicular cells by pretreatment with Ca 2+-Mg 2+-free Barth's medium. Total Rb + uptake consisted of an oubain-sensitive and an ouabain-insensitive flux. In the presence of 100 nmol/1 NaCl and 0.1 mmol/l ouabain the ouabain-insensitive flux amounted to 754.7 ± 59.9 pmol/oocyte per h ( n = 30 cells , i.e., 10 cells each from three different animals). In the absence of Na + (Na + substituted by N- methylglucamine ) or when Cl − was replaced by NO 3 − the ouabain-insensitive flux was reduced to 84.4 ± 42.9 and 79.2 ± 12.1 pmol/oocyte per h, respectively ( n = 50 cells ). Furthermore, this Na +- and Cl −-dependent flux was completely inhibited by 10 −4 mol/l bumetanide, a specific inhibitor of the Na +-K +-2Cl − cotransport system. These results suggest that K + uptake via a bumetanide-sensitive Na +-K +-2Cl − cotransport system represents a major K + pathway in oocytes.