CHARACTERIZATION OF REGULATORY VOLUME DECREASE IN THE THP-1 AND HL-60HUMAN MYELOCYTIC CELL-LINES

Exposure to hypotonic stress produces a transient increase in cell vol ume followed by a regulatory volume decrease (RVD) in both THP-1 and H L-60 cells. In contrast, cells exposed to hypotonic stress in a high K /low Na Hanks' solution not only failed to volume regulate, but displa yed a secondary swelling. Thus, while an outward K gradient was requir ed for RVD, the secondary swelling indicated that hypotonic stress inc reased permeability in the absence of a negative membrane potential. T he K channel blocker quinine (1-4 mM) blocked RVD in both cell types. Gramicidin's ability to overcome the quinine block of RVD indicated th at RVD is mediated by a quinine-sensitive cation transport mechanism t hat is independent of the swelling-induced anion transport mechanism. Barium (1-4 mM), another K channel blocker, slowed the rate of RVD, wh ile 4-aminopyridine, charybdotoxin, tetraethylammonium chloride, tetra butylammonium chloride, and gadolinium had no effect on RVD. Furthermo re, RVD was not mediated by calcium-activated conductances, since it o ccurred normally in Ca-free medium, in medium containing cadmium, and in BAPTA-loaded cells. Gramicidin produced little or no volume change in isotonic medium, suggesting that basal C1 permeability of both THP- 1 and HL-60 cells is low. However, swelling induced an anion efflux pa thway that is permeable to both chloride and bromide, but is impermeab le to methanesulfonate and glutamate. The anion channel blocker 3,5-di iodosalicylic acid (DISA) antagonized RVD in both cell types. In concl usion, RVD in THP-1 and HL-60 cells is mediated by independent anion a nd cation transport mechanisms that involve both a DISA-sensitive anio n pathway and a quinine-inhibitable K efflux pathway, neither of which requires increases in intracellular calcium to be activated. (C) 1994 Wiley-Liss, Inc.