Osmotic regulation of intestinal epithelial Na(+)-K(+)-Cl- cotransport: role of Cl- and F-actin.
Previous data indicate that adenosine 3',5'-cyclic monophosphate activates the epithelial basolateral Na(+)-K(+)-Cl- cotransporter in microfilament-dependent fashion in part by direct action but also in response to apical Cl- loss (due to cell shrinkage or decreased intracellular Cl-). To further address the actin dependence of Na(+)-K(+)-Cl- cotransport, human epithelial T84 monolayers were exposed to anisotonicity, and isotopic flux analysis was performed. Na(+)-K(+)-Cl- cotransport was activated by hypertonicity induced by added mannitol but not added NaCl. Cotransport was also markedly activated by hypotonic stress, a response that appeared to be due in part to reduction of extracellular Cl- concentration and also to activation of K+ and Cl- efflux pathways. Stabilization of actin with phalloidin blunted cotransporter activation by hypotonicity and abolished hypotonic activation of K+ and Cl- efflux. However, phalloidin did not prevent activation of cotransport by hypertonicity or isosmotic reduction of extracellular Cl-. Conversely, hypertonic but not hypotonic activation was attenuated by the microfilament disassembler cytochalasin D. The results emphasize the complex interrelationship among intracellular Cl- activity, cell volume, and the actin cytoskeleton in the regulation of epithelial Cl- transport.
Matthews
J B
JB
Department of Surgery, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts 02215, USA.
Smith
J A
JA
Mun
E C
EC
Sicklick
J K
JK
D000199:Actins / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D002712:Chlorides / Q000378:metabolism*; D015638:Cytochalasin D / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D010590:Phalloidine / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D012413:Rubidium / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism*; D028021:Sodium-Potassium-Chloride Symporters; D014882:Water-Electrolyte Balance
D000199:Actins; D002352:Carrier Proteins; D002712:Chlorides; D008565:Membrane Proteins; D028021:Sodium-Potassium-Chloride Symporters; D010590:Phalloidine; D015638:Cytochalasin D; D012964:Sodium; D012413:Rubidium; D011188:Potassium