Chloride and potassium channels in U937 human monocytes

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Abstract
Summary 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 CH3SO −4 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) presentin 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.