Influence of external K+ on potassium efflux in isolated chicken enterocytes.
1. Efflux of K+ was measured in pre-loaded (86Rb+) chicken enterocytes incubated in buffers with external K+ concentration ([K+]0) between 1 and 40 mM. 2. A decrease in [K+]0 from 6 to 1 mM reduced the rate constant of K+ efflux, whereas it was stimulated by increasing [K+]0 from 6 to 40 mM. 3. The inhibitory effect of low [K+]0 on K+ efflux was: (i) higher than that expected from a change in the electrical driving force, suggesting that membrane K+ permeability has been decreased, and (ii) attenuated by A23187 and Na(+)-free buffers. 4. The effect of A23187 on K(+)-induced K+ efflux was abolished by apamin and that of Na(+)-free buffers by apamin, quinine or verapamil, which suggests that the effect of low K+ on K+ efflux seems to be due to decreased intracellular Ca2+ concentration. 5. The stimulatory effect of 40 mM K0+ on K+ exit can be accounted for by an increase in the electrical driving force. 6. The efflux of K+ at 40 mM K0 appears to occur through Ca2(+)-activated K+ channels (KCa) since it was prevented by 500 microM quinine and unaffected by bumetanide or 3,4-diaminopyridine. 7. In addition, the current results show that an increase in external K+ concentration reduced the ability of quinine to inhibit KCa channels, and even abolished that of Ba2+ and apamin.
Department Fisiología y Biología Animal, Facultad de Farmacia, Universidad de Sevilla, Spain.
M C
MC
Montero
J
J
Bolufer
A
A
Ilundáin
D000818:Animals; D001030:Apamin / Q000494:pharmacology; D001464:Barium / Q000494:pharmacology; D001693:Biological Transport, Active / Q000187:drug effects; D000001:Calcimycin / Q000494:pharmacology; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000166:cytology; D008564:Membrane Potentials; D011188:Potassium / Q000378:metabolism* / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D011803:Quinine / Q000494:pharmacology; D012413:Rubidium / Q000378:metabolism
D015221:Potassium Channels; D001030:Apamin; D001464:Barium; D000001:Calcimycin; D011803:Quinine; D012413:Rubidium; D011188:Potassium