Cell volume-induced changes in K+ transport across the rat colon.
The effect of cell swelling and cell shrinkage on K+ transport across the rat colonic epithelium was studied by measuring unidirectional fluxes, uptake and efflux of 86Rb+, a marker for K+. Exposure to a hypotonic medium stimulated the secretory, serosa-to-mucosa flux of K+, whereas exposure to a hypertonic medium inhibited the absorptive, mucosa-to-serosa flux of K+ in the distal, but not in the proximal colon. Neither manoeuvre had any effect on the uptake of K+ across the apical or the basolateral membrane. Cell swelling induced a sustained increase in the apical and basolateral K+ efflux from both colonic segments, whereas cell shrinkage reduced the efflux. Ba2+ (10(-2) mol l(-1)) inhibited the swelling-induced stimulation of the apical, quinine (10(-3) mol l(-1)) that of the basolateral K+ efflux in the distal colon. Incubation of the tissue in Ca2+-free buffer or La3+, which blocks Ca2+-influx into the epithelium, strongly reduced the basal K+ efflux across the basolateral membrane. The same was observed with brefeldin A, a blocker of the transport of newly synthesized proteins out of the endoplasmatic reticulum. Swelling-induced K+ efflux, however, was not reduced. In the presence of colchicine, an inhibitor of the polymerization of microtubules, swelling evoked only a transient increase in mucosal efflux, which, especially in the proximal colon, fell after 6 min to the level of the isotonic control period. These results demonstrate that the cell volume is involved in the regulation of transepithelial K+ transport across the rat colonic epithelium and suggest a role of the cytoskeleton in the control of a part of the volume-sensitive K+ channels.
Ribeiro
R
R
Institut für Veterinär-Physiologie, Justus-Liebig-Universität Giessen, Giessen, Germany.
Heinke
B
B
Diener
M
M
D000818:Animals; D001464:Barium / Q000494:pharmacology; D001692:Biological Transport / Q000502:physiology; D020126:Brefeldin A / Q000494:pharmacology; D048429:Cell Size / Q000502:physiology*; D003078:Colchicine / Q000494:pharmacology; D003106:Colon / Q000187:drug effects / Q000378:metabolism*; D003599:Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D007038:Hypotonic Solutions; D007413:Intestinal Mucosa / Q000187:drug effects / Q000378:metabolism; D007552:Isotonic Solutions; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D011803:Quinine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012413:Rubidium
D007038:Hypotonic Solutions; D007552:Isotonic Solutions; D015221:Potassium Channels; D020126:Brefeldin A; D001464:Barium; D011803:Quinine; D012413:Rubidium; D011188:Potassium; D003078:Colchicine