CHLORIDE AND POTASSIUM CHANNELS IN U937 HUMAN MONOCYTES

Ionic channels in a human monocyte cell line (U937) were studied with the inside-out patch-clamp technique. A Ca2+-activated K+ channel and three Cl--selective channels were observed. The Ca2+-activated K+ channel had an inward-rectifying current-voltage relationship with slope conductance of 28 pS, and was not dependent on membrane potential. Among the three Cl- channels, and outward-rectifying 28-pS channel was most frequently observed. The permeability ratio (Cl-/Na+) was 4-5 and CH3SO4- was also permeant. The channel became less active with increasing polarizations in either direction, and was inactive beyond ±120 mV. The channel, observed as bursts, occasionally had rapid events within the bursts, suggesting the presence of another mode of kinetics. Diisothiocyanatostilbene-disulfonic acid (DIDS) blocked the channel reversibly in a dose-dependent manner. The second 328-pS Cl- channel had a linear currentvoltage relationship and permeability ratio (Cl-/Na+) of 5-6. This channel became less active with increasing polarizations and inactive beyond ±50 mV. DIDS blocked the channel irreversibly. The channel had multiple subconductance states. The third 15-pS Cl- channel was least frequently observed and least voltage sensitive among the Cl- channels. Intracellular Ca2+ or pH affected none of the three Cl- channels. All three Cl- channels had a latent period before being observed, suggesting inhibitory factor(s) present in situ. Activation of the cells with interferon-γ, interferon-αA or 12-O-tetradecanoylphorbol-13-acetate (TPA) caused no change in the properties on any of the channels. © 1990 Springer-Verlag New York Inc.