Transmembrane potential of renal papillary epithelial cells: effect of urea and DDAVP

To define how renal papillary epithelial cells respond to wide changes in the ionic and osmotic composition of their environment, measurements were made of the transmembrane potential differences (PD) of rat renal papillary epithelial cells in vitro in media containing 100 mM NaCl, 100 mM KCl, 1.5 mM CaCl2, and 1 mM MgSO4 plus varying amounts of urea and/or sucrose up to 1,400 mM. Glass microelectrodes (resistance 25-75 M Omega) were used. With added sucrose, no change in PD from the initial value of -9.3 +/- 1.3 (SD) mV (n = 29) (cell interior negative) was found. With added urea, alone or while osmolality was maintained nearly constant with sucrose, the PD changed in a triphasic manner, depolarizing to -5.3 mV at 50 mM urea, hyperpolarizing to -20.0 mV at 150 mM urea, and then depolarizing again to -5.5 mV at 1,400 mM urea. When bath potassium was decreased to 10 meQ/liter (choline replacement) the PD hyperpolarized to -46.9 +/- 5.0 (SD) mV (n = 32). DDAVP, a nonpressor vasopressin analogue, and 8-bromo-cAMP depolarized the membrane to -5 mV in the presence of urea but did not change PD when urea was absent. These observations suggest an interaction between urea and ionic movement or conductance in rat renal papillary epithelial cells.