IMMUNOLOGICALLY ACTIVATED CHLORIDE CHANNELS INVOLVED IN DEGRANULATION OF RAT MUCOSAL MAST-CELLS

Crosslinking of type I Fc-epsilon-receptors (Fc-epsilon-RI) on the surface of basophils or mast cells initiates a cascade of processes leading to the secretion of inflammatory mediators. We report here a correlation between mediator secretion and the activation of Cl- channels in rat mucosal-type mast cells (line RBL-2H3). Stimulation of RBL cells by either IgE and antigen or by a monoclonal antibody specific for the Fc-epsilon-RI, resulted in the activation of Cl- ion channels as detected by the patch-clamp technique. Channel activation occurred slowly, within minutes after stimulation. The channel has a slope conductance of 32 pS at potentials between 0 and -100 mV, and an increasing open-state probability with increasing depolarization. Activation of apparently the same Cl- channels could be mimicked without stimulation by isolating inside-out membrane patches in tyrode solution. Parallel inhibition of both Cl- channel activity and mediator secretion, as monitored by serotonin release, was observed by two compounds, the Cl- channel blocker 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) and the anti-allergic drug cromolyn. NPPB inhibited both the antigen-induced Cl- current and the serotonin release, where half-maximal inhibition occurred at similar doses, at 52-mu-M and 77-mu-M, respectively. The drug cromolyn, recently found to inhibit immunologically induced mediator secretion from RBL cells upon intracellular application, also blocks Cl- channels (IC50 = 15-mu-M) when applied to the cytoplasmic side of an inside-out membrane patch. The observed Cl-channel activation upon immunological stimulation and the parallel inhibition of channel current and of serotonin release suggests a functional role for this Cl- channel in mediator secretion from the mast cells studied.