Osmotic pressure regulates abg-rENaC expressed in Xenopus oocytes

Ji, Hong-Long, Catherine M. Fuller, and Dale J. Benos. Osmotic pressure regulates abg-rENaC expressed in Xenopus oocytes. Am. J. Physiol. 275 (Cell Physiol. 44): C1182–C1190, 1998.—The hypothesis that amiloride-sensitive Na1 channels (ENaC) are involved in cell volume regulation was tested. Anisosmotic ND-20 media (ranging from 70 to 450 mosM) were used to superfuse Xenopus oocytes expressing abg-rat ENaC (abg-rENaC). Whole cell currents were reversibly dependent on external osmolarity. Under conditions of swelling (70 mosM) or shrinkage (450 mosM), current amplitude decreased and increased, respectively. In contrast, there was no change in current amplitude of H2O-injected oocytes to the above osmotic insults. Currents recorded from abg-rENaC-injected oocytes were not sensitive to external Cl2 concentration or to the K1 channel inhibitor BaCl2. They were sensitive to amiloride. The concentration of amiloride necessary to inhibit one-half of the maximal rENaC current expressed in oocytes (Ki; apparent dissociation constant) decreased in swollen cells and increased in shrunken oocytes. The osmotic pressure-induced Na1 currents showed properties similar to those of stretch-activated channels, including inhibition by Gd31 and La31, and decreased selectivity for Na1. abg-rENaC-expressing oocytes maintained a nearly constant cell volume in hypertonic ND-20. The present study is the first demonstration that abg-rENaC heterologously expressed in Xenopus oocytes may contribute to oocyte volume regulation following shrinkage.