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Induction of 86 Rb Fluxes by Ca 2+ and volume changes in thymocytes and their isolated membranes
Author(s) -
Grinstein S.,
Cohen S.,
Sarkadi B.,
Rothstein A.
Publication year - 1983
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/jcp.1041160313
Subject(s) - trifluoperazine , vesicle , chemistry , intracellular , ionophore , membrane , calmodulin , biophysics , ouabain , tonicity , efflux , biochemistry , sodium , biology , enzyme , organic chemistry
Cell swelling and elevated intracellular Ca 2+ 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 + ( 86 Rb) were stimulated by hypotonicity. Addition of A23187 plus Ca 2+ also increased 86 Rb fluxes. Ca 2+ ‐ and volume‐induced 86 Rb 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 86 Rb in an osmotically active compartment of ∼1.3 μl/mg protein. Equilibrium exchange fluxes of 86 Rb in the vesicles were unaffected by Ca 2+ with or without A23187. Calmodulin had no effect on 86 Rb permeability but stimulated ATP‐dependent Ca 2+ accumulation. Hypotonic swelling increased both uptake and efflux of 86 Rb from vesicles. However, this increase was not blocked by either quinine or trifluoperazine, was not specific for K + ( 86 Rb), and is probably unrelated to RVD. It is concluded that components essential for the volume‐ and Ca 2+ ‐induced changes in K + permeability are lost or inactivated during membrane isolation. An intact cytoarchitecture may be required for RVD.