Cytoplasmic pH is differently regulated in the monoblastic U-937 and erythroleukemic K-562 cell lines.
Regulation of cytoplasmic pH (pHi) of the human monoblastic U-937 and erythroleukemic K-562 cell lines was investigated. The apparent resting pHi, as assessed by the fluorescent pH probe quenel, were 6.61 and 6.75 for the U-937 and K-562 cells, respectively. When extracellular Na+ was substituted by equimolar choline+, pHi decreased by about 0.2 units. The protein kinase C activating beta-form of the phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate (TPA; 10(-10) and 10(-7) M) induced a dose-dependent alkalinization in both cell types of 0.03-0.12 units, whereas the alpha-form was inactive. The response was detectable after about 2 min and reached steady-state 10-15 min later. In the K-562 cells the alkalinization was mediated by Na+/H+ exchange as it was accompanied by stimulation of H+ extrusion and abolished by Na+ removal. The TPA response in the U-937 cells, however, was unaffected by Na+ removal, not accompanied by H+-efflux, and thus unrelated to Na+/H+ exchange. Since electron microscopy indicated development of multivesicular bodies with an acidic interior, the alkalinization can probably be accounted for by an intracellular mechanism. Ionomycin (10(-5) M) induced a rapid increase in the cytoplasmic Ca2+ concentration of both cell types and this response was accompanied by acidification followed by a Na+-dependent recovery. In the U-937, but not in the K-562, cells this recovery was followed by a net alkalinization. It is concluded that both cell types possess a Na+/H+ exchange of importance for pHi but that this mechanism is regulated differently in the U-937 and K-562 cells.
Forsbeck
K
K
Department of Pathology, University Hospital, Uppsala, Sweden.
Nygren
P
P
Larsson
R
R
Nilsson
M
M
Nilsson
K
K
Gylfe
E
E
D002118:Calcium / Q000502:physiology*; D002352:Carrier Proteins / Q000502:physiology; D002451:Cell Compartmentation; D002460:Cell Line; D003593:Cytoplasm / Q000502:physiology; D004987:Ethers / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015759:Ionomycin; D004915:Leukemia, Erythroblastic, Acute / Q000503:physiopathology*; D007942:Leukemia, Experimental / Q000503:physiopathology*; D008854:Microscopy, Electron; D009000:Monocytes / Q000502:physiology*; D017923:Sodium-Hydrogen Exchangers; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D002352:Carrier Proteins; D004987:Ethers; D017923:Sodium-Hydrogen Exchangers; D015759:Ionomycin; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium