Selective expression of potassium channels during mast cell differentiation.

In rodents, mast cell progenitors differentiate into distinct mucosal and serosal phenotypes which differ markedly in their functional responses to antigenic and peptidergic stimulation. Although the molecular basis of mast cell differentiation or functional specialization is unknown, it is possible that regulation of calcium entry contributes to one or both processes. The prolonged secretory response of mucosal mast cells (MMC) and the antigen-elicited synthesis of interleukin-3 by immature MMC both require a rise of cytoplasmic calcium sustained by Ca2+ influx across the plasma membrane. This Ca2+ entry is highly sensitive 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 in the prototype serosal mast cell from rat peritoneum. An inwardly rectifying K+ conductance was constitutively active and a latent outwardly rectifying K+ conductance was elicited rapidly upon ligation of cell surface adenosine or P2 purinergic receptors linked to G proteins of the Gi family. Stimulation of P2 receptors dramatically potentiated 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.