Volume-induced increase of anion permeability in human lymphocytes.

Abstract

Peripheral blood mononuclear cells (PBM) readjust their volumes after swelling in hypotonic media. This regulatory volume decrease (RVD) is associated with a loss of cellular K + and is thought to be promoted by an increased permeability to this ion. In contrast, no change in volume was observed when K + permeability of PBM in isotonic media was increased to comparable or higher levels using valinomycin. Moreover, valinomycin-induced 86Rb+ loss in K+-free medium was considerably slower than in K+-rich medium. These results suggest that anion conductance limits net salt loss in isotonic media. Direct measurements of relative conductance confirmed that in volume-static cells, anion conductance is lower than that of K +. In volume-regulating cells depolarization occurred presumably as a result of increased anion conductance. Accordingly, the effiux of a6CI from PBM was markedly increased by hypotonic stress. Since both membrane potential and intracellular ant1 concentration are reduced in hypotonically swollen cells, the increased efflux is probably due to a change in CI-permeability. Anions and cations seem to move independently through the volume-induced pathways: the initial rate ofsnRb uptake in swollen cells was not affected by replacement of external C1-by SO7; conversely, 36C1 fluxes were unaffected by substitution of K + by Na +. The data indicate that anion conductance is rate-determining in salt and water loss from PBM. An increase in anion conductance is suggested to be the critical step of RVD of human PBM.

Ca(2+)‐activated K+ channels in rat thymic lymphocytes: activation by concanavalin A.

“…It is possible that Ca2+ influx through these channels is responsible for the small depolarization observed after block of the Ca2+-gated K+ conductance by CTX or BAPTA (Figs 1 C and 2). However, we cannot at present exclude the involvement of other electrogenic pathways in the mitogenic response: for example activation of a Cl-conductance in these cells would also produce a depolarization from the resting potential (Grinstein,524 ConA-STIMULATED Ca2_-ACTIVATED K+ CHANNELS Clarke, Dupre & Rothstein, 1980). Failure to detect such other conductances in cellattached patches following ConA stimulation can be explained if the activated channels have a low density or a small unitary conductance, or the conductance change results from a change in the current carried by an electrogenic pump.…”

Role of volume-regulated and calcium-activated anion channels in cell volume homeostasis, cancer and drug resistance

“…7,12,13 That cell swelling transiently activates electrogenic anion permeability was first described in Ehrlich ascites tumor cells (EATC) 10 and in lymphocytes. 14 Figure 1A illustrates Cl -efflux under isotonic, hypotonic and hypertonic conditions, and it has been determined that under isotonic conditions less than 5% represents conductive Cl -flux with the rest being electroneutral anion exchange (AE). 15 In contrast, increased Clflux under swollen and shrunken conditions represent Cl -conductance (VRAC) and electroneutral Cl -transport via the Na, K,2Cl cotransporter (NKCC), respectively.…”

Cl- Permeabilities in Red Blood Cells and Peripheral Blood Lymphocytes from Cystic Fibrosis and Control Subjects

“…A mononuclear cell fraction was separated from peripheral blood by the method of Grinstein et al (9). Briefly, heparinized whole blood was diluted 5050 with RPMI 1640 tissue culture medium and then layered over Ficoll-Hypaque (Histopaque 1077, Sigma Chemicals).…”

“…In the RBC, ion and water movement across valinomycin-treated cells reflect conductive C1-flows (13,14). In the PBL, volume regulatory changes in response to an isosmotic medium have been used to study conductive paths for K+ and C1- (9,10). Because an abnormality in C1-channels might be generalized to blood elements in CF subjects, we compared the magnitude and regulation of conductive C1-paths in RBCs and PBLs from CF subjects with those from control (normal) subjects.…”