Regulatory volume decrease in HL-60 cells: importance of rapid changes in permeability of Cl- and organic solutes.
Results obtained through the use of inhibitors and isotope flux and equilibration techniques indicate that the regulatory volume decrease (RVD) response of human promyelocytic leukemic HL-60 cells occurs largely through the efflux of K+ and Cl- through separate conductive membrane pathways. These "channels" differ pharmacologically and in their modes of activation from those described in lymphocytes and Ehrlich ascites tumor cells. With use of measured 86Rb+ and 36Cl- fluxes, together with a diffusion kinetic model, the membrane potential (Em) and apparent K+ and Cl- permeabilities (PK and PCl) were estimated under various isotonic and hypotonic conditions. Under isotonic (300 mosM) conditions, Em is close to the Nernst potential for K+ and PCl is < 0.1 PK. Rapid and steeply graded increases in the measured Cl- efflux rate and calculated PCl occur with decreasing tonicity, with the largest increases at tonicities < 80% of isotonic. K+ efflux and the apparent PK increase only modestly with decreasing tonicity. At 50% tonicity, PCl rises to nearly 10 times PK, which should cause substantial membrane depolarization, with Em approaching the Nernst potential for Cl-. Gramicidin treatment markedly accelerates the rate of RVD and net 36Cl- efflux in hypotonic Na(+)-and Cl(-)-free media, providing further evidence that PK is rate limiting during RVD. K+ loss exceeds Cl- loss during RVD, and the total loss of K+ and Cl- is insufficient to account for the observed degree of volume recovery in 50% tonicity media, indicating that other (organic) osmolytes must take part in the HL-60 cell RVD response.
Hallows
K R
KR
Department of Biophysics, University of Rochester Medical Center, New York 14642.
Knauf
P A
PA
D002118:Calcium / Q000493:pharmacokinetics; D002463:Cell Membrane Permeability; D002712:Chlorides / Q000493:pharmacokinetics*; D003470:Culture Media; D006801:Humans; D007038:Hypotonic Solutions / Q000494:pharmacology; D015473:Leukemia, Promyelocytic, Acute / Q000473:pathology*; D011188:Potassium / Q000493:pharmacokinetics; D012413:Rubidium / Q000493:pharmacokinetics; D014407:Tumor Cells, Cultured; D014882:Water-Electrolyte Balance
D002712:Chlorides; D003470:Culture Media; D007038:Hypotonic Solutions; D012413:Rubidium; D011188:Potassium; D002118:Calcium