EGF and PGE2 inhibit rabbit CCD Na+ transport by different mechanisms: PGE2 inhibits Na(+)-K+ pump.
The rabbit cortical collecting duct absorbs Na+ by a transport system comprised of an apical membrane Na+ channel and a basolateral membrane Na(+)-K(+)-adenosinetriphosphatase. The rate of Na+ absorption across this epithelium is acutely inhibited by several hormones and autacoids including epidermal growth factor (EGF) and prostaglandin E2 (PGE2). We used electrophysiological analysis to determine which Na+ transport mechanism is primarily regulated in response to EGF and PGE2. We used concentrations of EGF and PGE2 that inhibited Na+ absorption to a comparable degree. We assessed the effects of these agents on Na+ transport primarily by the calculated equivalent current; the validity of this indicator was verified using simultaneous tracer flux measurements. EGF and PGE2 had different effects on the intracellular electrophysiological parameters. EGF (in the presence of a cyclooxygenase inhibitor) hyperpolarized the apical membrane voltage in a manner analogous to the Na(+)-channel blocker amiloride, reduced the transepithelial conductance, and increased the fractional resistance of the apical membrane. In comparison, PGE2 depolarized the apical membrane voltage in a manner analogous to the Na(+)-K+ pump inhibitor ouabain, and caused no significant changes in transepithelial conductance or apical membrane conductance. The finding that EGF hyperpolarized the apical membrane indicates that this agent attenuates Na+ absorption by reducing apical Na+ entry due to a decrease in the magnitude of the apical membrane Na+ conductance. In contrast, the electrophysiological changes produced by PGE2 indicate primary inhibition of the basolateral Na(+)-K+ pump following PGE2 treatment.
Warden
D H
DH
Department of Veterans Affairs Medical Center, Iowa City, Iowa.
Stokes
J B
JB
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002462:Cell Membrane / Q000502:physiology / Q000648:ultrastructure; D015232:Dinoprostone / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D004848:Epithelium / Q000378:metabolism / Q000502:physiology / Q000648:ultrastructure; D005260:Female; D007685:Kidney Tubules, Collecting / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D010042:Ouabain / Q000494:pharmacology; D011817:Rabbits; D012964:Sodium / Q000493:pharmacokinetics*; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects / Q000502:physiology*
D010042:Ouabain; D004815:Epidermal Growth Factor; D000584:Amiloride; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D015232:Dinoprostone