F64^hASIC1a exhibits long opening events and a subconductance state. (A) Representative example of an excised outside-out membrane patch containing a large number of channels activated by external pH 7.1 for 1 min. (B) Representative example of excised outside-out membrane patches containing a single channel activated by pH 7.2. Dashed lines indicate three current levels: closed (C), subconductance (S), and fully open (O). The subconductance state appears when channels transition to the open and to the closed states. Holding potential, −60 mV. External solution 100 mM Na⁺; pipette solution 100 mM K⁺. The shown trace represents 1 out of 15 patches, all showing the subconductance state. (C) All-points histogram of a continuous recording of activity of a single channel exhibits three conductance states of magnitude: 0, 0.7, and 1.5 pA. The line is the Gaussian fit to the data. (D) Histogram of duration of opening events in seconds. (E) Representative example of multichannel hASIC1a patch activated with pH 6.5. (F) Representative examples of unitary currents. (G) All-points histogram of a continuous recording of activity of a single channel exhibits two conductance states of magnitude: 0 and 1.5 pA. (H) Histogram of duration of opening events of WT hASIC1a.