Epithelial K channel expressed in Xenopus oocytes is inactivated by protein kinase C.
K homeostasis is maintained in higher animals by epithelia of the kidney and intestine. Little is known regarding the molecular regulation of K secretion. We injected Xenopus oocytes with mRNA from teleost intestine, a K-secreting epithelium with apical membrane K channels. Oocytes expressed a conductance that displayed whole-cell current properties with the following characteristics: marked selectivity for K over Na and Cl, voltage-independent kinetics, Ca insensitivity, tonic activation, and inward rectification in symmetrical K. Barium, quinine, and tetraethylammonium blocked the conductance, whereas apamin, charybdotoxin, and 4-aminopyridine did not. The K conductance was rapidly (t1/2 = 10 min) and completely inactivated by 4 beta-phorbol 12-myristate 13-acetate but not by 4 alpha-phorbol 12,13-didecanoate. Sucrose density gradient fractionation revealed that mRNA required for expression is in the 1- to 2-kilobase size range, suggesting the possibility that a single subunit encodes the channel. The K conductance expressed from injection of size-fractionated mRNA was identical in all respects to that seen using unfractionated mRNA, including response to 4 beta-phorbol 12-myristate 13-acetate. The results suggest that protein kinase C regulates K secretion in epithelia by modulation of apical K channels.
Sullivan
S K
SK
Department of Medicine, Columbia University College of Physicians and Surgeons, New York, NY 10032.
Swamy
K
K
Greenspan
N R
NR
Field
M
M
D000818:Animals; D004848:Epithelium / Q000502:physiology; D005260:Female; D005432:Flounder; D007422:Intestines / Q000502:physiology; D007700:Kinetics; D008565:Membrane Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D009865:Oocytes / Q000502:physiology*; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D011493:Protein Kinase C / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000302:isolation & purification; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014982:Xenopus laevis
D008565:Membrane Proteins; D015221:Potassium Channels; D012333:RNA, Messenger; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate