Human peripheral blood lymphocytes (PBL), when placed into hypotonic media, first swell and then shrink back to their original volumes because of a rapid KCl leakage via volume-activated K* and anion permeation pathways . By using gramicidin, a cation channel-forming ionophore, cation transport through the cell membrane can be shunted so that the salt fluxes and thus the volume changes are limited by the rate of the net anion movements. The "gramicidin method," supplemented with direct measurements of volumeinduced ion fluxes, can be used to assess the effects of drugs and of various treatments on cation and anion permeabilities . It is demonstrated that quinine and cetiedil are much more effective blockers of volume-induced K* transport than of Cl -transport, while dipyridamole, DIDS, and NIP-taurine inhibit only volume-induced Cl -movement . Oligomycins block both cation and anion transport pathways, oligomycin A being more effective in inhibiting K* transport and oligomycin C preferentially blocking Cl-movement . Ca depletion of PBL abolishes volume-induced K + transport but has no effect on Cl-transport .Repletion of cell calcium by ionophore A23187 immediately restores rapid K + transport without significantly affecting volume-induced Cl -transport . These observations, taken together with other reported information, can be best explained by a model in which cell swelling activates independent CI -and K + conductance pathways, the latter being similar in properties to the CaY+-activated K + transport observed in various cell membranes .

The regulatory volume decrease of osmotically swollen human peripheral blood lymphocytes can be inhibited by agents acting on volume-activated K+- or Cl--transport pathways. Quinine, cetiedil, and 3,3'-dipropylthiadicarbocyanine were found to block the volume-induced K+ transport by interaction with sites on the outside face of the membrane, perhaps by competition with external K+. Drugs known to influence calmodulin action inhibit both volume-induced K+ and Cl- transport to varying degrees. Those inhibitors, particularly of K+ transport, are correlated with their calmodulin-antagonist activity. Penetrating sulfhydryl (SH) reagents (in contrast to nonpenetrating ones) are potent inhibitors of both volume-induced K+ and Cl- movements, indicating the presence of functionally important SH groups located within the membrane or at the cytoplasmic face. A number of agents, such as dipyridamole and oligomycin C, are specific inhibitors of the volume-activated anion pathway. In all respects studied, the inhibition characteristics of the volume-activated K+ pathway of lymphocytes resemble those of the Ca2+-activated K+ channel of red cells. In contrast, the volume-induced anion permeability differs from the primary anion-transport pathway of red cells.

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