K-INDUCED EXPANSION OF HUMAN HEMATOPOIETIC PROGENITORS( CHANNEL ANTISENSE OLIGODEOXYNUCLEOTIDES INHIBIT CYTOKINE)

Primitive human hemopoietic progenitor cells identified by surface mem brane markers CD33(-)CD34(+) are capable of expansion into lineage-res tricted precursors following in vitro stimulation by hemopoietic regul ators such as stem cell factor (SCF) and interleukin-3 (IL-3). In sear ch of ionic currents involved in cytokine-induced progenitor cell grow th and differentiation, human umbilical cord blood CD33(-)CD34(+) cell s were subjected to perforated patch-clamp recordings following overni ght incubation with SCF and/or IL-3. An inward rectifying potassium ch annel (K-ir) was found in 33% of control unstimulated cells, in 34% of cells incubated with IL-3, in 31% of cells incubated with SCF and in 75% of cells incubated with IL-3 plus SCE K-ir activity increased with elevation of extracellular potassium and was blocked by extracellular Cs+ or Ba2+. Antisense oligodeoxynucleotides directed against K-ir bl ocked both mRNA and functional expression of K-ir channels, K-ir antis ense also inhibited the in vitro expansion of cytokine-stimulated CD33 (-)CD34(+) cells into erythroid (BFU-E) and myeloid (GM-CFU) progenito rs in 7-day suspension cultures. Extracellular Cs+ or Ba2+ induced a s imilar degree of inhibition (40-60%) of progenitor cell generation. Th ese findings strongly suggest an essential role for K-ir in the proces s of cytokine-induced primitive progenitor cell growth and differentia tion.