Single-channel properties of a stretch-sensitive chloride channel in the human mast cell line HMC-1

A stretch-activated (SA) Cl(−) channel in the plasma membrane of the human mast cell line HMC-1 was identified in outside-out patch-clamp experiments. SA currents, induced by pressure applied to the pipette, exhibited voltage dependence with strong outward rectification (55.1 pS at +100 mV and an about tenfold lower conductance at −100 mV). The probability of the SA channel being open (P (o)) also showed steep outward rectification and pressure dependence. The open-time distribution was fitted with three components with time constants of τ(1o) = 755.1 ms, τ(2o) = 166.4 ms, and τ(3o) = 16.5 ms at +60 mV. The closed-time distribution also required three components with time constants of τ(1c) = 661.6 ms, τ(2c) = 253.2 ms, and τ(3c) = 5.6 ms at +60 mV. Lowering extracellular Cl(−) concentration reduced the conductance, shifted the reversal potential toward chloride reversal potential, and decreased the P (o) at positive potentials. The SA Cl(−) currents were reversibly blocked by the chloride channel blocker 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS) but not by (Z)-1-(p-dimethylaminoethoxyphenyl)-1,2-diphenyl-1-butene (tamoxifen). Furthermore, in HMC-1 cells swelling due to osmotic stress, DIDS could inhibit the increase in intracellular [Ca(2+)] and degranulation. We conclude that in the HMC-1 cell line, the SA outward currents are mediated by Cl(−) influx. The SA Cl(−) channel might contribute to mast cell degranulation caused by mechanical stimuli or accelerate membrane fusion during the degranulation process.