Abstract: | Previous data indicate that adenosine 3',5'-cyclicmonophosphate activates the epithelial basolateralNa+-K+-Cl cotransporter in microfilament-dependent fashion in part by direct action but also in response to apicalCl loss (due to cellshrinkage or decreased intracellularCl ). To further addressthe actin dependence ofNa+-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 extracellularCl concentration and alsoto activation of K+ andCl efflux pathways.Stabilization of actin with phalloidin blunted cotransporter activationby hypotonicity and abolished hypotonic activation ofK+ andCl efflux. However,phalloidin did not prevent activation of cotransport by hypertonicityor isosmotic reduction of extracellularCl . Conversely, hypertonicbut not hypotonic activation was attenuated by the microfilamentdisassembler cytochalasin D. The results emphasize the complexinterrelationship among intracellularCl activity, cell volume,and the actin cytoskeleton in the regulation of epithelialCl transport. |