Cell volume-induced changes in K+ transport across the rat colon

• Published in: Acta physiologica Scandinavica 2001-04, Vol.171 (4), p.445-458
• Main Authors: Ribeiro, R., Heinke, B., Diener, M.
• Format: Article
• Language: English
• Subjects: Animals; Barium - pharmacology; Biological and medical sciences; Biological Transport - physiology; Brefeldin A - pharmacology; Ca2; Cell Size - physiology; cell volume; Colchicine - pharmacology; colon; Colon - drug effects; Colon - metabolism; cytoskeleton; Cytoskeleton - drug effects; Cytoskeleton - metabolism; electrolyte transport; Fundamental and applied biological sciences. Psychology; Hypotonic Solutions; Intestinal Mucosa - drug effects; Intestinal Mucosa - metabolism; Intestine. Mesentery; Isotonic Solutions; K+ channels; K+ transport; Potassium - metabolism; Potassium Channels - drug effects; Potassium Channels - physiology; Quinine - pharmacology; rat; Rats; Rats, Wistar; Rubidium; Vertebrates: digestive system
• ISSN: 0001-6772; 1365-201X
• DOI: 10.1046/j.1365-201X.2001.00806.x

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.