title: Induction of 86Rb fluxes by Ca2+ and volume changes in thymocytes and their isolated membranes.
abstract: Cell swelling and elevated intracellular Ca2+ increase K+ permeability in lymphocytes. Experiments were performed to test whether these effects can also be elicited in isolated plasma membrane vesicles. Rabbit thymocytes, used as a source of membrane vesicles, were found to regain their volume after swelling in hypotonic, low-K+ media. This regulatory volume decrease (RVD) was inhibited by quinine and trifluoperazine, but not affected by ouabain. Both efflux and uptake of K+ (86Rb) were stimulated by hypotonicity. Addition of A23187 plus Ca2+ also increased 86Rb fluxes. Ca2+- and volume-induced 86Rb fluxes were also studied in isolated membranes. A plasma membrane-rich vesicle fraction, enriched over 11-fold in 5'-nucleotidase, was isolated from thymocytes. The vesicles were about 35% inside-out and trapped 86Rb in an osmotically active compartment of approximately 1.3 microliter/mg protein. Equilibrium exchange fluxes of 86Rb in the vesicles were unaffected by Ca2+ with or without A23187. Calmodulin had no effect on 86Rb permeability but stimulated ATP-dependent Ca2+ accumulation. Hypotonic swelling increased both uptake and efflux of 86Rb from vesicles. However, this increase was not blocked by either quinine or trifluoperazine, was not specific for K+ (86Rb), and is probably unrelated to RVD. It is concluded that components essential for the volume- and Ca2+-induced changes in K+ permeability are lost or inactivated during membrane isolation. An intact cytoarchitecture may be required for RVD.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002463:Cell Membrane Permeability / Q000187:drug effects; D007038:Hypotonic Solutions; D008297:Male; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D011803:Quinine / Q000494:pharmacology; D011817:Rabbits; D011868:Radioisotopes / Q000378:metabolism*; D012413:Rubidium / Q000378:metabolism*; D013601:T-Lymphocytes / Q000187:drug effects / Q000378:metabolism*; D014268:Trifluoperazine / Q000494:pharmacology
chemical_list: D002147:Calmodulin; D007038:Hypotonic Solutions; D011868:Radioisotopes; D014268:Trifluoperazine; D010042:Ouabain; D011803:Quinine; D012413:Rubidium; D011188:Potassium; D002118:Calcium