Expression of amiloride-sensitive Na+ channels of hen lower intestine in Xenopus oocytes: electrophysiological studies on the dependence of varying NaCl intake.
Epithelial Na+ channels were incorporated into the plasma membrane of Xenopus laevis oocytes after micro-injection of RNA from hen lower intestinal epithelium (colon and coprodeum). The animals were fed either a normal poultry food which contained NaCl (HS), or a similar food devoid of NaCl (LS). Oocytes were monitored for the expression of amiloride-sensitive sodium channels by measuring membrane potentials and currents. Oocytes injected with poly(A)+RNA prepared from HS animals or non-injected control oocytes showed no detectable sodium currents, whereas oocytes injected with LS-poly(A)+RNA had large amiloride-blockable sodium currents. These currents were almost completely saturated by sodium concentrations of 20 mM with a Km of about 2.6 mM sodium. Amiloride (10 microM) inhibits the expressed sodium channels entirely and examination of dose response relationships yielded a half-maximal inhibition concentration (Ki) of 120 nM amiloride. I-V difference curves in the presence or absence of sodium or amiloride (10 microM) indicate a potential dependence of the sodium transport which can be described by the Goldman equation. When Na+ is replaced by K+, no amiloride response was detected indicating a high selectivity for Na+ over K+. These results provide strong evidence that intestinal Na+ channels are regulated by dietary salt intake on the RNA level.
Weber
W M
WM
Institut für Tierphysiologie, Justus-Liebig-Universität Giessen, Germany.
Asher
C
C
Garty
H
H
Clauss
W
W
D000584:Amiloride / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000818:Animals; D004594:Electrophysiology; D005260:Female; D007413:Intestinal Mucosa / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D011061:Poly A / Q000235:genetics; D011188:Potassium / Q000378:metabolism; D012313:RNA / Q000378:metabolism; D015222:Sodium Channels / Q000187:drug effects*; D012965:Sodium Chloride / Q000378:metabolism*; D014981:Xenopus
D015222:Sodium Channels; D011061:Poly A; D012965:Sodium Chloride; D012313:RNA; D000584:Amiloride; D011188:Potassium