Site and mechanism of action of epidermal growth factor in rabbit cortical collecting duct

Abstract

To examine the exact target cell and mechanism of action of epidermal growth factor (EGF) in the isolated cortical collecting duct from rabbit kidney, we compared electrical properties of collecting duct (CD) cells (principal cells) and intercalated (IC) cells in absence and presence of EGF at 10(-8) M. Differentiation of CD and IC cells was based on values of basolateral membrane voltage (Vb) and fractional apical membrane resistance (fRa). In CD cells, upon addition of EGF to bath, lumen-negative transepithelial voltage (VT) was decreased from -8.0 +/- 1.9 to -2.4 +/- 1.3 mV (n = 22, P less than 0.001), but Vb was little changed (from -85.1 +/- 2.8 to -83.1 +/- 2.7 mV, n = 19), indicating that EGF in bath mainly caused changes in apical membrane voltage. In addition, peritubular EGF increased transepithelial resistance (RT) from 132.9 +/- 15.8 to 153.8 +/- 18.4 omega.cm2 (n = 16, P less than 0.001) as well as fRa from 0.31 +/- 0.06 to 0.39 +/- 0.07 (n = 12, P less than 0.01). These actions of EGF were prevented by pretreatment with 50 microM luminal amiloride. Luminal EGF had no effects on VT, Vb, RT, or fRa of CD cells. In IC cells, upon addition of EGF to bath, neither Vb nor fRa was affected. From these results, we conclude that EGF acts on the CD cell at the basolateral border and inhibits mainly the amiloride-sensitive Na+ conductance in the apical membrane.

Effects of uninephrectomy on electrical properties of the cortical collecting duct from rabbit remnant kidneys.

“…Slices of the coronary section 1-2-mm thick were made and transferred to a dish containing a cold intracellular fluid-like solution ofthe following composition (mM): 14 KCl, 44 K2HPO4, 14 KH2PO4, 9 NaHCO3, and 160 sucrose. The CCD segments were isolated and perfused in vitro according to the method of Burg et al (22) with slight modifications in this laboratory ( 13,14). Briefly, the tubule segment was perfused via a perfusion pipette inserted into one end ofthe tubule.…”

“…The transepithelial and cellular electrical properties ofthe tubule were measured using techniques described previously by Muto et al ( 13,14,16). In brief, the transepithelial voltage (VT) was measured through the perfusion pipette, which was connected to one channel of a dual-channel electrometer (Duo 773; W-P Instruments, Inc., New Haven, CT) with a 3 M KCI-3% agar bridge and a calomel half-cell electrode.…”

“…Both voltages were referenced to the bath and were recorded on a four-pen chart recorder (R64; Rikadenki, Tokyo, Japan). Cable analysis was used to calculate the transepithelial conductance ( GT ), and the fractional apical membrane resistance (fRA) as described in detail previously (9,10,(13)(14)(15)(16). Constant-current pulses, 50 nA (300 ms in duration, 10-s interval), were injected into the tubule lumen via the perfusion pipette.…”

“…Electrical identification of CD cells was performed according to the criteria described previously by Muto et al (13)(14)(15)(16). CD cells have a relatively lowerfRA; higher VB, apical Na', and K+ conductances; and basolateral K+ and Cl-conductances.…”

“…These adaptive changes also included an increase in Na+/K+ ATPase activity (6,7) and an amplification ofthe basolateral membrane area ofthe collecting duct (CD) cell (8). These findings suggest that the CD cell, which is mainly responsible for Na+ and K+ transports in the CCD (9)(10)(11)(12)(13)(14)(15)(16), would play the key role in the adaptation after reduction of renal mass. However, the cellular mechanisms of these adaptive changes remain unknown.…”