K⁺ channel antisense oligodeoxynucleotides inhibit cytokine-induced expansion of human hemopoietic progenitors

Primitive human hemopoietic progenitor cells identified by surface membrane markers CD33^-CD34⁺ are capable of expansion into lineage-restricted precursors following in vitro stimulation by hemopoietic regulators such as stem cell factor (SCF) and interleukin-3 (IL-3). In search of ionic currents involved in cytokine-induced progenitor cell growth and differentiation, human umbilical cord blood CD33 CD34⁺ cells were subjected to perforated patch-clamp recordings following overnight incubation with SCF and/or IL-3. An inward rectifying potassium channel (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 SCF. K_ir activity increased with elevation of extra-cellular potassium and was blocked by extracellular Cs⁺ or Ba²⁺. Antisense oligodeoxynucleotides directed against K_ir blocked both mRNA and functional expression of K_ir channels. K_ir antisense also inhibited the in vitro expansion of cytokine-stimulated CD33^-CD34⁺ cells into erythroid (BFU-E) and myeloid (GM-CFU) progenitors in 7-day suspension cultures. Extracellular Cs⁺ or Ba²⁺ induced a similar degree of inhibition (40-60%) of progenitor cell generation. These findings strongly suggest an essential role for K_ir in the process of cytokine-induced primitive progenitor cell growth and differentiation.