Volume regulatory responses of basolateral membrane vesicles from Necturusenterocytes: Role of the cytoskeleton

Previous studies from this laboratory have demonstrated that basolateral me mbrane vesicles isolated from Necturus maculosus small intestinal epithelia l cells possess a K+ channel that is inhibited by ATP. In the present studi es, we demonstrate that these vesicles, which are essentially devoid of sol uble cytoplasmic contaminants, exhibit volume regulatory responses that par allel those of intact epithelial cells, Thus, suspension of these vesicles in a solution that is hypotonic to the intravesicular solution increases ch annel activity whereas suspension in a solution that is hypertonic to the i ntravesicular solution decreases, and may abolish, channel activity. These volume regulatory responses appear to be mediated by the same K-ATP channel and depend on an intact actin cytoskeletal network. The responses to both hypotonic and hypertonic challenge are abolished by cytochalasin D or by in cubating the vesicles under conditions that are known to depolymerize actin , Phalloidin, which is known to stabilize actin filaments, partially preven ts the action of cytochalasin D, Thus, the present results indicate that th e K-ATP channel activity of basolateral membrane vesicles from Necturus bas olateral membranes respond to hypo- and hypertonic challenge monotonically around an isotonic "set point" and that these responses depend on an intact actin cytoskeleton.