SELECTIVE EXPRESSION OF POTASSIUM CHANNELS DURING CELL-DIFFERENTIATION

In rodents, mast cell progenitors differentiate into distinct mucosal and serosal phenotypes which differ markedly in their functional respo nses to antigenic and peptidergic stimulation. Although the molecular basis of mast cell differentiation or functional specialization is unk nown, it is possible that regulation of calcium entry contributes to o ne or both processes. The prolonged secretory response of mucosal mast cells (MMC) and the antigen-elicited synthesis of interleukin-3 by im mature MMC both require a rise of cytoplasmic calcium sustained by Ca2 + influx across the plasma membrane. This Ca2+ entry is highly sensiti ve to membrane potential, affording a possible site for regulation of mast cell function by receptor-linked ion channels. We found that rat interleukin-3-dependent bone marrow-derived mast cells of the mucosal phenotype expressed two K+ conductances, neither of which is present i n the prototype serosal mast cell from rat peritoneum. An inwardly rec tifying K+ conductance was constitutively active and a latent outwardl y rectifying K+ conductance was elicited rapidly upon ligation of cell surface adenosine or P-2 purinergic receptors linked to G proteins of the G(i) family. Stimulation of P2( )receptors dramatically potentiat ed antigen-triggered secretion in a pertussis toxin-sensitive manner, suggesting that activation of the outwardly rectifying K+ channel may regulate antigen-dependent functions of MMC.